2.9 stroker pinging

[Gunni]

Get a scope into the cylinders to see if there is any scoring on the bores.
That will instantly resolve any potential piston size problems.

[GeoffBob]

Also, I'm a machinist by trade and taking under 0.003" or 0.075mm out of the bores will be very difficult, if you're getting new pistons you may as well go up 0.5mm on the bore.

I am no machinist, but I would imagine that the only way to do it would be to grind the bore? The final cut on my gears, for example, is so fine that it has to be ground on.

I agree though that 0.5mm up makes sense.

[e301988325i]

Also, I'm a machinist by trade and taking under 0.003" or 0.075mm out of the bores will be very difficult, if you're getting new pistons you may as well go up 0.5mm on the bore.

I am no machinist, but I would imagine that the only way to do it would be to grind the bore? The final cut on my gears, for example, is so fine that it has to be ground on.

I agree though that 0.5mm up makes sense.

It's more the alignment or realignament that's the issue, making sure you remove metal all the way down the bore to ensure it's perfectly round.

Setting up a block for a 0.001" or 0.0015" skim on diamter, for 6 bores, **** that!!!!!!!! I'd go at least 0.25mm bigger if you want to re-bore that block.

[Sebastian35]

Thanks for you help guys! And also making me feel like..... it is my own fault....
When i brought the pistons i did order the piston to suit my 885 Head, and 85mm bore.its in black and with on emails. little did i know i would get something else and be sweet talked into using them.

It has all been a learning curve, as i trusted the maker to make something for the said spec! Its never happened before ie: Every part we buy for a car is made to measure and should do as it says on the box! How many parts do we buy and have to shave thing to get them to fit. None! If i was advised to wait for the pistons to arrive before boring The block ,because quality was an issue, I sure would have!

I am at the point where i do not care if the pistons will work or not by shaving here or there. Its easier to call Top End and get them to send again what i wanted in the first place.
I did question the difference between my standard piston from the day they arrived! I always new trouble was ahead!

As for the size i may as well do as you guys have said go bigger to 85.5 or 86.
If Top end do not look after me then I will go elsewhere.

[Sebastian35]

Get a scope into the cylinders to see if there is any scoring on the bores.
That will instantly resolve any potential piston size problems.

This engine takes a good 4mins to get rid of piston slap as it is and its never got hot so i doubt there is a clearance problem. all will be revealed on removal...

Thanks for the advice mate...

[GeoffBob]

Thanks for you help guys! And also making me feel like..... it is my own fault....

Sebastian, that was not the intention, at least it most certainly was not my intention. My interest in this and any thread where I provide advice is in finding the route cause of the problem and curing it, not blaming anyone for it. My interest is mechanical (for this is where may fascination lays), not social or political.

[GeoffBob]

It's more the alignment or realignament that's the issue, making sure you remove metal all the way down the bore to ensure it's perfectly round.

I understand. I did not consider the problem of realignment. Makes perfect sense what you say.

[GeoffBob]

I am at the point where i do not care if the pistons will work or not by shaving here or there. Its easier to call Top End and get them to send again what i wanted in the first place. I did question the difference between my standard piston from the day they arrived! I always new trouble was ahead!

If TopEnd have already sent the wrong pistons once I wouldn't go back to them. They are an agent for JE pistons, as I would expect are Cambridge Motorsport (as recommended by Ezagood). If I were you I'd place my order with Cambridge and deal local (Ezagood seems happy?).

This engine takes a good 4mins to get rid of piston slap as it is and its never got hot so i doubt there is a clearance problem.

If you have four minutes worth of piston slap then you don't have a clearance issue!

[Sebastian35]

Out of interest to all reading this thread I will document whats needed to find out the cause of the Cr of this engine!

[gooner1]

Without pre empting either Sebastians or X=Works conclusions, this would
appear to be at least the second time that JE, or rather their agents, have supplied almost the complete opposite of Pistons that were ordered.
It won't solve your problem, Sebastian, but it might alleviate your feelings of guilt if you take a look
at X-works build thread in the Chat section, page 24 specifically.


http://www.e30zone.net/modules.php?name ... c&t=108356

Good luck with it all.

[Gunni]

Get a scope into the cylinders to see if there is any scoring on the bores.
That will instantly resolve any potential piston size problems.

This engine takes a good 4mins to get rid of piston slap as it is and its never got hot so i doubt there is a clearance problem. all will be revealed on removal...

Thanks for the advice mate...

If the bores are not scored and it takes that long for the slap to go away then this is no way a piston clearance issue, the static compression or dynamic if you will is simply to high for whatever fuel you are using.

The quickest solution would be a thicker headgasket, you can get them in a varity of sizes so one of them should suit you.

If the head comes off then measure the volume of the head chamber and the volume the piston takes up, you might have a head that has been skimmed 3 too many times or wrong pistons.

[e301988325i]

Thanks for you help guys! And also making me feel like..... it is my own fault....
When i brought the pistons i did order the piston to suit my 885 Head, and 85mm bore.its in black and with on emails. little did i know i would get something else and be sweet talked into using them.

It has all been a learning curve, as i trusted the maker to make something for the said spec! Its never happened before ie: Every part we buy for a car is made to measure and should do as it says on the box! How many parts do we buy and have to shave thing to get them to fit. None! If i was advised to wait for the pistons to arrive before boring The block ,because quality was an issue, I sure would have!

I am at the point where i do not care if the pistons will work or not by shaving here or there. Its easier to call Top End and get them to send again what i wanted in the first place.
I did question the difference between my standard piston from the day they arrived! I always new trouble was ahead!

As for the size i may as well do as you guys have said go bigger to 85.5 or 86.
If Top end do not look after me then I will go elsewhere.

Hi Sebastian,

I just want to come from a different perspective; I do not neccessarily think topend have supplied you with terribly incorrect pistons. You have come to a marque specific forum, and are getting very specialist advice on a standard fit engine.

Hairy screech sharing his M20 flow bench testing makes us very lucky, most do it for profit or to win racing and thus keep it secret. It was after all him that concluded the offset bowl pistons were best, and also to leave the head's combustion chamber well alone. This knowledge, if you look at the dates on his thread, is relatively new (apart from BMW who did it right in the first place obviously). For example, to roughly quote HS on the alpina engines of the day, 'It's like the guy that did the head didn't talk to the guy who did the pistons'.

[Sebastian35]

Today I have checked the valve timing in relation to the crank and all is well.
Next i removed the head and i can clearly see that the bores are tight! even though it appears if you rock them there is a lot of clearance!

I have spoke with Top end and they are adamant that they can supply a piston to suit a any given bore size, and it be perfect!
So either my machine shop or Top End have it wrong!
But I should have checked all there work myself!

Just to check things further I have the measurements from the block. Piston travel from deck hight to max lift is 2.37mm + Crank stroke of 84mm, head gasket is stock .070ins and head is holding 42cc. Can someone calculate my CR.

[Sebastian35]

I agree e301988325i! The only way to get the higher compression i wanted was for them to send me a Flat Top piston! apparently the bowl type will foul the valves before they reach the required compression I wanted....

[GeoffBob]

Today I have checked the valve timing in relation to the crank and all is well.

That is good to hear Sebastian, well done! Please feel free to mail me your measurements (cam lift vs crank angle) and I’d be happy to graph them and post up a polar-plot of your cam (if that is what you would like).

Next i removed the head and i can clearly see that the bores are tight! even though it appears if you rock them there is a lot of clearance!

What makes you think they are tight Sebastian? Any visible marks? Please feel free to send pics. Any chance you could measure your bores with a T-bore gauge and micrometer?

I have spoke with Top end and they are adamant that they can supply a piston to suit a any given bore size, and it be perfect! So either my machine shop or Top End have it wrong! But I should have checked all there work myself!

It’s a possibility that you asked for a piston to fit an 85mm bore and they supplied you with a piston with 85mm OD, not one with 85mm less clearance (a mistake on their part), but that sounds extreme to me. That’s hardly a recipe for 4 minutes of piston slap. It’d be more likely to seize after 4 minutes come to think of

Just to check things further I have the measurements from the block. Piston travel from deck hight to max lift is 2.37mm + Crank stroke of 84mm, head gasket is stock .070ins and head is holding 42cc. Can someone calculate my CR.

You’ll need to drop the piston an exact distance down into the block (measured with a dial gauge) and then measure the volume (cc’s) of the piston crown same as you did the head. This has to be done since we have no way of knowing the volume of the valve cut-outs in the piston crown. Drop the piston down exactly 5mm, say, indicated by the dial gauge (deck to piston crown), and then measure the cc’s it takes to fill the volume on top of the piston with white spirit. Be sure to wipe a thin smear of Vaseline around the edge of the piston first to seal up the gap else the spirit will leak past and spoil your measurement. Also, be sure to cut yourself a small flat disc of clear Perspex or polycarbonate with a hole drilled in the centre through which you can fill the top of the cylinder with spirit. Seal the disc to the top of the cylinder with another thin smear of Vaseline and then start filling the volume through the hole with white spirit from a graduated pipette till the spirit rises to the filler hole. Take note, you have to do it this way or else your measurement will be rendered useless by the meniscus (due to fluid surface tension) that forms on the top of the spirit.

If you did not already do it this way, this is how you should also measure the head volume, also with a wipe of Vaseline around the edge of the valves. FYI, the stock head volume is 40cc (assuming no skimming), not 42cc, so it is possible that your recorded 2cc (or more) more than was actually there because of the meniscus on the fluid. As with the block, seal the clear Perspex or polycarbonate disc to the head with a thin smear of Vaseline. I know it doesn’t sound like much, but 2cc will make a big difference to your CR. Try measure down to the nearest half cc if possible.

With these measurements we can determine your static CR.

Best of Luck
Geoff

[GeoffBob]

Two pics here of how its done. White (methylated) spirit with purple dye already added works well for this test. A proper graduated glass pipette is more accurate than using a syringe, but both work.



In this pic here, performed on a VW combi head, you can see that an extra hole has been drilled in the perspex to let the air bubble out.

[Sebastian35]

My engine is still in the car! And as it's angled I cannot perform the bore cc task. I will try and send you a picture of the bores tomorrow. There are visible marks where the skirt would travel, not major but there in all bores! However if you rock then side to side there is plenty of movement but maybe not at skirt. I am sure its it just a tiny clearance issue as like you said it would have sezied up already....

I don't think I will try again with these pistons! I will definitely order some bowl tops even if I can't have the high CR I wanted. This time I will get the pistons in had first! If I thought I could get them to work I would put then into another block as I have another spare engine. But it would be a shame to pull a good motor!

[GeoffBob]

My engine is still in the car! And as it's angled I cannot perform the bore cc task. !

Actually you can. Cut yourself a disc of clear Perspex (about 5mm thick will do) to fit over a cylinder, at least a cm or more bigger than the bore so that you can get it to seal with Vaseline along the shoulder of the bore. Drill two holes into the perspex, roughly 3mm diameter each. Locate one at the upper edge of the cylinder and one at the bottom. Use a graduated syringe to inject your white spirit into the cylinder through the bottom hole. The air bubble will then rise to the highest point and escape out the top hole. If the bottom hole isn’t perfectly aligned it doesn’t matter as the spirit will go in no problem. The top hole must, however, be aligned with the top (highest) edge of the cylinder for all the air to escape. Slide the disc around on its Vaseline seal to get it to locate correctly (with one of the two holes at the highest point). Obviously, the nose of the syringe must be pushed into the hole in the perspex so that it seals, else the spirit will simply leak out.

I know it sounds like a PITA, but I would honestly recommend that you do this measurement as this is the last piece in the puzzle in order to calculate your actual CR. You’ll need at least a 50cc syringe from the chemist, a bit of old clear Perspex and a bottle of purple dyed white spirit. Not much really.

I will try and send you a picture of the bores tomorrow. There are visible marks where the skirt would travel, not major but there in all bores! However if you rock then side to side there is plenty of movement but maybe not at skirt. I am sure its it just a tiny clearance issue as like you said it would have sezied up already....

I am sorry to hear this Sebastian, sad news indeed. Remember that when the piston is cold it is tapered (wider at the bottom than at the top) which is why you can move it around. Simply because the top looks clear doesn’t mean the skirt isn’t. Once again, sorry to hear this.

I don't think I will try again with these pistons! I will definitely order some bowl tops even if I can't have the high CR I wanted. This time I will get the pistons in had first! If I thought I could get them to work I would put then into another block as I have another spare engine. But it would be a shame to pull a good motor!

Maybe e301988325i can tell us how long it would take to hone away 30micron from a cylinder bore and whether it would be worth trying, or indeed even recommended to try. I recon that 30micron off your bores (professionally honed at a machine shop, not using a drill at home) and some potential machining to your head and piston crowns (depending on what your static CR turns out to be) and you’d breathe new life into your engine. On the other hand I can fully understand why you would have your heart set on a set of properly matched pistons.

[e301988325i]

I agree e301988325i! The only way to get the higher compression i wanted was for them to send me a Flat Top piston! apparently the bowl type will foul the valves before they reach the required compression I wanted....

Read that to yourself, then look at X-works' pistons excessive valve recesses, to see what is possible, ie offset bowls with valve cut outs.

[Maybe e301988325i can tell us how long it would take to hone away 30micron from a cylinder bore and whether it would be worth trying, or indeed even recommended to try. I recon that 30micron off your bores (professionally honed at a machine shop, not using a drill at home) and some potential machining to your head and piston crowns (depending on what your static CR turns out to be) and you’d breathe new life into your engine. On the other hand I can fully understand why you would have your heart set on a set of properly matched pistons.

Possible, but 0.03mm off the diameter is a LOT of honing. I would guess at 1/2 hour per bore, likely more, but this isn't my field, as I'm not a grinder myself (very different to machining).

At work we only hone small bores, under 25mm diameter, which we machine to 0.001" tolerance and then hone to perfection which easily takes 5-10 mins a bore, but it's very fine work.

Worth investigating if you need to, but if you can afford to consider new pistons then another overbore can't be out of budet and this is the best way to go IMHO.

[Sebastian35]

Hi Guys this will be my last post for a few weeks as om off on holiday!
If i mention this car on holiday my life will not be worth living LOL!

Anyway I have sent off an original standard piston to cambridge motorsport! They have the job of suppling the new pistons, They need the old one for a pattern of the bowl top! so it looks like i will get the right ones in the end. It will take 4 to 6 weeks for the new set to arrive, the new pistons will be 85.5mm and, then i can get the block re-bored to suit the new set. Hopefully all will be well this time round!

If anyone would like the old pistons for a project then they can have then for the postage costs!
I am not going to mess for a month while i wait for the new ones, this gives me time to get back in my other halfs good books . Then i will be back at work in the work shop. So if you message me and I like your project then a set of forged flat tops can be yours.........! You need a 84mm crank and 135mm rods. Remember flat tops pistons not best suited to 885 head.

As for Top End performance, F...... in waste of time. The only time i got a response was when i called them!

Catch you in a few weeks guys!

[CHR1S1990]

did you get round to measuring the volume of the piston crown? Just wondering how you were actually sitting CR wise - anybody you donate the pistons to would have to bore out their 84mm block before finding out.

sorry to hear about the extra expense!

[Sebastian35]

did you get round to measuring the volume of the piston crown? Just wondering how you were actually sitting CR wise - anybody you donate the pistons to would have to bore out their 84mm block before finding out.

sorry to hear about the extra expense!

I do not have a t-bar and micrometer big enough!
I have arranged to take the block once i have new pistons and they will do it while i am present! not buying tools i would only use once. i will leave the machining and measuring work to the machinist!

[GeoffBob]

T-bar and micrometer not required Sebastian. Only syringe, bit of perspex, white spirit and Vaseline (see my earlier description). Oh, and a dial gauge to set the depth of the piston in the block.

It's the final piece in the puzzle. After all the effort we have put into trying to solve this one for you I for one would really like to know what the CR of this engine actually turned out to be

The burning quation is, was the engine knocking because the CR was actually too high (higher than the specified 11.2:1) or was it just because the pistons were tight and the compression pressure was thus too high.

If it turned out to be the latter then there is a good chance that your engine would be back on its feet, ping free, after a decent hone!

[reggid]

T-bar and micrometer not required Sebastian. Only syringe, bit of perspex, white spirit and Vaseline (see my earlier description). Oh, and a dial gauge to set the depth of the piston in the block.

It's the final piece in the puzzle. After all the effort we have put into trying to solve this one for you I for one would really like to know what the CR of this engine actually turned out to be

The burning quation is, was the engine knocking because the CR was actually too high (higher than the specified 11.2:1) or was it just because the pistons were tight and the compression pressure was thus too high.

If it turned out to be the latter then there is a good chance that your engine would be back on its feet, ping free, after a decent hone!

i have a hard time believing a flat top piston would create a high enough static CR to cause the symptoms he has been observing. You would have to have skimmed a couple mm from the head. My guess is that due to the severity of the problem that more than one issue is it play.

I do agree that with all the help and advice given it would be good to knowthe actual problrmn i.e what was the CR and what were the valve timings. At the very least it might someone else falling down the same trap

[GeoffBob]

i have a hard time believing a flat top piston would create a high enough static CR to cause the symptoms he has been observing. You would have to have skimmed a couple mm from the head. My guess is that due to the severity of the problem that more than one issue is it play.

I do agree that with all the help and advice given it would be good to know the actual problrmn i.e what was the CR and what were the valve timings. At the very least it might someone else falling down the same trap

He's already measured the protrusion of his pistons above his deck and measured his head volume for us Reggid. At 42cc there is no way that head has been excessively skimmed. On an 85mm bore 1mm will account for 5.7cc of volume. Now if he'd just measure that volume on top of the crown as I described to him earlier then we'd know for sure what his static CR is. Then we'd have this thread tidied up nicely imo .

[CHR1S1990]

Now if he'd just measure that volume on top of the crown as I described to him earlier then we'd know for sure what his static CR is. Then we'd have this thread tidied up nicely imo .

exactly. even though it looks like he has decided on different pistons (good seeing as though he seems to have the money), these pistons may well give a low enough CR for somebody else to use

The burning quation is, was the engine knocking because the CR was actually too high (higher than the specified 11.2:1) or was it just because the pistons were tight and the compression pressure was thus too high.

for what its worth, i think that if (deduced by the above test) the pistons do give a CR of near the quoted 11.2 , i dont think there would be such a problem with the pinging Seb describes on the 99RON he is using - the bore is most likely problem here as you say geoff

[CHR1S1990]

By my calculations (usually flawed), if you depress the piston 5mm down from TDC, you should measure between 24.6cc and 25.2cc of fluid using the method Geoff kindly described for the claimed 11.2:1 CR.

This assumes a few things:
Ӣ the headgasket thickness you supplied is its compressed thickness
Ӣ your headgasket bore is somewhere between 85.0mm and 86.0mm
Ӣ if you measure your head volume again (taking into account the meniscus as in Geoffs demo) it is actually 40cc

[e301988325i]

Two of the pics that Sebastian mailed me showing his flat-top JE pistons:

I reckon with a bit of planning I could put an offset bowl in those. If you're serious about donating them? I have the crank from Chr1s1990 and the 135mm rods from my b25 sounds like a plan!!

[GeoffBob]

By my calculations (usually flawed), if you depress the piston 5mm down from TDC, you should measure between 24.6cc and 25.2cc of fluid using the method Geoff kindly described for the claimed 11.2:1 CR.

To achieve a static CR of 11.2:1 we require a compressed volume of 46.75cc. If the head contributes 40cc and the 1.8mm thick gasket a further 10cc, then the piston crown is required to displace a total of (40cc + 10cc) ”“ 46.75cc = 3.25cc of volume above the deck. Now, if we drop the piston 5mm from TDC into the block then any difference in the measured fluid volume required to fill the space above the piston and the 28.4cc that would otherwise fill a 5mm high volume in an 85mm bore must be due to the volume of the piston crown. Since the crown is required to displace 3.25cc of the 50cc due to the head and gasket, then we would expect to measure a volume, by my calculation, of 28.4cc ”“ 3.25cc = 25.15cc. So yes, I am in agreement with your calculation.

Take note, however, that this does of course depend upon where you measure the displacement of the piston into the bore from. If you happen to start with the piston flush with the deck (not quite TDC) then the additional 2.37mm of crown protrusion above the deck (that Sebastian measured) must be factored back into the calculation. TBH, where he measures from (true to deck or TDC) really doesn’t bother me (as long as he states which), a measurement either way would be nice.

If I get a quiet moment today I’ll try and estimate the volume of those valve pockets and squish-band (based on pics and posted dimensions) myself and see what numbers materialise. Anyone know the size of Sebastian’s valves? I seem to recall he said he fitted oversize, and I doubt he is going to reply as I think he has already gone off on holiday.

[CHR1S1990]

Thanks for checking Geoff. I arrived at my "boundary" values as I am not sure the actual size of his HG bore. Furthermore I have just created an excel spreadsheet to calculate static CR very easily should anybody else want it.

[Sebastian35]

No! still here off in the early hours...
The valves are +1mm oversize...
as for the engine when I get back and have it on a stand I will try and measure the volume and head again!
I checked the cc of the head by putting it on the bench got it level and then filled it with a syringe until full, no perspex and only 10mm at a time syringe, hence an extra few cc. Either way the head could not have been skimmed to excess.

I am sure if I shaved here and there and whatever else they may work. I have limited time and that is why I will be buying new pistons, and in any case I would still have pistons that do not match the head.

zone member Chris1990 will be having the JE pistons in question as soon as I get them out! he will be using a shorter stroke so should be prefect for his low comp project......

Here is a picture of the project car. thanks for hosting it Geoff....
ftp://ftp.csir.co.za/DPSS/Landwards_Sci ... G_0127.jpg

[CHR1S1990]

Cool car Seb

well, based on my calculations again..

I am currently building a 2.7 which will be supercharged in the future. After speaking to you geoff, it was agreed that a compression ratio of 8.8:1 would be suitable for such a build, also considering I am running on LPG.

Using the eta 81mm crank in a b25 block, bored out to fit Sebs 85mm pistons and using the stated 135mm rods, would give me a compression ratio of 8.2:1 (and a displacement of 2.8L) using the stock 1.778mm head gasket - a little lower than I wanted.

Using a 1mm MLS headgasket would bring it up to 8.8:1 - lovely.

Im assuming the rods will clear the bottoms of the bores with the -3mm stroke however.

[ezagood]

Since it's a Sunday today and I have little or nothing else to do I did a quick calculation. If you were to purchase a set of JE pistons same as Ezagood's (with dome and dish to match the 885 head), that is to say with 53.3cc of compressed volume at TDC, then with a stroke of 84mm, a bore of 85mm and a stock gasket you'd finish up with static CR of 9.94:1, as good as 10:1. Provided you bore the block correctly you should measure a compression pressure of dead bang on 200psi.

did it today. 10 puffs brought it up to 225psi. i can see where your calcs went wrong though. im 85.5mm bore.

[GeoffBob]

Since it's a Sunday today and I have little or nothing else to do I did a quick calculation. If you were to purchase a set of JE pistons same as Ezagood's (with dome and dish to match the 885 head), that is to say with 53.3cc of compressed volume at TDC, then with a stroke of 84mm, a bore of 85mm and a stock gasket you'd finish up with static CR of 9.94:1, as good as 10:1. Provided you bore the block correctly you should measure a compression pressure of dead bang on 200psi.

did it today. 10 puffs brought it up to 225psi. i can see where your calcs went wrong though. im 85.5mm bore.

What cam do you have Ezagood? In my calculation I simply assumed Sebastians cam since I don't know what cam you have on your engine.

On an 85.5mm bore I have you pushing 225psi at 14.7psi atmospheric pressure if your inlet valve is closing around 66' after BDC.

But I could be wrong ...

[ezagood]

284/272 i,o 32 i,c 72 e,o 66 e,c 26