2.9 stroker pinging

[Sebastian35]

I have just done a cold compresion and it was still 270psi crancking 5 times.
I think i have total seal rings!
If i crank the engine 6 to 8 times it can reach over 300psi?

You have me worried!

Im going to have pull the Head as i want to see inside now?

[GeoffBob]

I need to think about this some more, I’ll get back to you on this.

OK, here’s what I think.

Before we finally blame your static CR (and start looking at the best way to lower it) we need to ascertain that you indeed received the cam that TopEnd claim to have sent.

You need to start with a rudimentary check on the position of your cam. The fact that TopEnd claim that the inlet and exhaust have identical timing makes this test quite easy.

Having gone through the process of aligning the timing marks as per the usual cam-belt fitment procedure, manually crank your #1 cylinder to TDC at the end of the exhaust stroke, the exhaust and inlet cam lobes should now be located symmetrically either side of the cam followers, as shown in the diagram below. Check that your piston is indeed at TDC by feeling through the spark plug hole and rocking the crank back and forth to set the piston at TDC. Do be sure that you’re at the end of the exhaust (and not compression) stroke.

Now visually inspect the cam lobes to see that they are indeed aligned as shown below. I realise that this isn’t a particularly accurate method, but if you have skipped a tooth when fitting the belt, or TopEnd made a mess of your cam during manufacture, then your eye will be good enough to pick it up. Take note that the exact angle between the lobes that you see will not look the same as my diagram since there is an offset angle between the exhaust and inlet cam followers on the actual head. What is important, however, is that the cam lobes are symmetrically located either side of the followers. It’s easy to see if the cam is located symmetrically or not because if it is then you will have equal lift on both valves. Look at the diagram and you will see that at TDC at the end of the exhaust stroke the valves are busy crossing over (inlet is opening and exhaust is closing), but at exactly TDC the lift on both is identical. Check this! If it’s not as it should be then you’re valve timing is out.

The sort of thing that your looking for here is a mistake in the location of the sprocket relative to how the cam was ground. In other words, the cam may have the correct profile, but the blank was aligned incorrectly in the machine when the cam was ground, such that the profile is now offset relative to where it should be. A mistake that is sufficient to significantly alter your dynamic CR (at least to the extent that you have indicated) will be visible to the naked eye.



FYI, the angles in this diagram are correct relative to the crank shaft (not cam-shaft angles). Hence, one turn of the cam corresponds to two turns of the crank!

Check on this, report back, and then we’ll move onto the next test. This is likely leading up to an issue with your static CR, but we have to check everything along the way to be sure. You’re going to be hellishly p!ssed at me if I recommend you take 10cc out the top of a piston and then the problem doesn’t go away because it’s down to some altogether different cause.

[GeoffBob]

[GeoffBob]

I have covered 210 miles in the car whilst trying various things to fix issues!
I even drove to work a 80mile round trip with no issues other than the odd ping if i had go up a hill.
Drove constant on the by road for 20 mins at 60 mph and never getting hot!
If pistons were to tight surely it would quickly get hot?

So how did she drive, flat or OK? If you’re only picking up the odd ping going up hill then your problem does not sound as severe as I understood from your earlier posts. I am beginning to think you simply need to get your car on a dyno and get it properly tuned. A qualified tuner with an AFR gauge and timing light will soon be able to tell you if you have compression related issues due to the amount of retard that he has to put on your ignition timing. I suspect that you are not only currently running the wrong timing map, but that you could also be running lean under load.

I’d still suggest measuring up your cam timing with a dial gauge (as I described on page 2) so that you are confident that you in fact have no cam timing issues.

[ezagood]

ill be comp testing mine when i get my new plugs. im interested in the result. my pistons are 1.5mm over size with a stock low comp shaped crown. piston hight is stock. i calculated 10 to 1

[Sebastian35]

When the pistons arrived I did measure them, i think they were 94.5 or 94.45... From skirt to skirt, when i measured 180 degrees from the skirt they were a bit smaller! The originals were 94.8
I did not record the measurements. Would that sound about right.
I did ask Top End if they were the correct pistons for an 85mm bore....


When I drove the car it was ok at 2500 rpm a little lumpy getting there I never pushed it.
At load it would ping!

Since I read you message telling me not to drive I haven't tried it again!

Tomorrow I will see if I cam measure the cam. At the least I can measure opening and closing and view the position of the cam lobes.

[GeoffBob]

ill be comp testing mine when i get my new plugs. im interested in the result. my pistons are 1.5mm over size with a stock low comp shaped crown. piston hight is stock. i calculated 10 to 1

And some seriously good looking pistons you have there too Ezagood! So I take it the change in CR is down entirely to the change in stroke and slightly bigger bore? 10:1 should work quite nicely.

[GeoffBob]

When the pistons arrived I did measure them, i think they were 94.5 or 94.45... From skirt to skirt, when i measured 180 degrees from the skirt they were a bit smaller! The originals were 94.8

So they were roughly 10mm bigger than what you ordered? Surely not?

I did not record the measurements. Would that sound about right.
I did ask Top End if they were the correct pistons for an 85mm bore....

I am curious as to how TopEnd suggested you fit a 95mm piston into an 85mm bore. OK, I’m guessing it’s a typo. Sorry, I thought maybe that was real for a moment. I’ll work out what the correct bore value should be for those measurements (less 10mm) you posted above and get back to you.

When I drove the car it was ok at 2500 rpm a little lumpy getting there I never pushed it. At load it would ping!

Since I read you message telling me not to drive I haven't tried it again!

I understand. I have since reread one of your earlier posts and it genuinely sounds as if you have only been able to make it this far on retarded ignition timing, Shell V-Power, and a load of tetraethyl-lead added. That’s no way to have to run a car. You might as well fill up on racing fuel once a week. We need to find a solution to this and I know (from the compression pressure you posted) that we are heading towards having to lower your static compression ratio. Unfortunately there are some bridges that you have to cross before we can conclude for certain that your best course of action is to take a mill to either a piston or your cylinder head.

Tomorrow I will see if I cam measure the cam. At the least I can measure opening and closing and view the position of the cam lobes.

At least start with the basic test that I described on page three Sebastian. It’s an easy test to do that requires no more than lifting the valve cover and a bit of spanner work. With a keen eye you’ll soon see if all is well with your cam or not.

I’ll get back to you with your ideal bore dimension.

[GeoffBob]

[Sebastian35]

All is pointing towards the Static CR!

If all is well with the Cam i will pull the head Monday morning!
In theory the bores should be marked if the pistons are to tight, right?

I find out from Top End what the correct skirt measurement is for my pistons.
Then I can measure the bore size when the head is off and take it from there!

Is it possible to check clearances of the pistons within the bore?

I must say for the time being we must take my measurements with a pinch of salt as the vernier caliper i used dose not measure in such small increments! I do have a good DTI gauge and a micrometer but its to small to fit around a piston.

[Sebastian35]

Geoff I have just checked the Cam timing and there position in relation to TDC are correct!
Have not got enough time to check angles today!

I am pertty sure the problem is with the bottom end, I always have done....
I just hope its a piston being too deep and needs shaving!
Then i will try a thicker gasket for the summer...
There is one thing for sure as soon as we locate the fault, if being a bore size issue, I will take the block to the Machine shop and let them sort it!
No more messing from me I am affraid....I just want to enjoy the summer as all is getting neglected around me as i have been consumed by this thing....

[ezagood]

ill be comp testing mine when i get my new plugs. im interested in the result. my pistons are 1.5mm over size with a stock low comp shaped crown. piston hight is stock. i calculated 10 to 1

And some seriously good looking pistons you have there too Ezagood! So I take it the change in CR is down entirely to the change in stroke and slightly bigger bore? 10:1 should work quite nicely.

exactly that sir .

[ezagood]

.I just want to enjoy the summer as all is getting neglected around me as i have been consumed by this thing....

i know how that feels.

[Sebastian35]

ill be comp testing mine when i get my new plugs. im interested in the result. my pistons are 1.5mm over size with a stock low comp shaped crown. piston hight is stock. i calculated 10 to 1

And some seriously good looking pistons you have there too Ezagood! So I take it the change in CR is down entirely to the change in stroke and slightly bigger bore? 10:1 should work quite nicely.

exactly that sir .

Yea we all know thing that are good looking tend to be bad for us Lol
Somewhere the info i had was wrong! if maybe the case the pistons are coming up that little to much, Thats what im thinking!
I have done a few milkes in it and if the bores were tight surely things would get very hot quickly!

[GeoffBob]

[GeoffBob]

ill be comp testing mine when i get my new plugs. im interested in the result. my pistons are 1.5mm over size with a stock low comp shaped crown. piston hight is stock. i calculated 10 to 1

And some seriously good looking pistons you have there too Ezagood! So I take it the change in CR is down entirely to the change in stroke and slightly bigger bore? 10:1 should work quite nicely.

exactly that sir .

Want me to do a pressure calculation for you Ezagood? We could wager 1£ as to whether or not I'll be with within 10psi of your measured value. I'll wager another 1£ on top of that, that you'll win the first £

[Sebastian35]

All is pointing towards the Static CR!

Yes, I do believe that is where we are heading.

If all is well with the Cam i will pull the head Monday morning!
In theory the bores should be marked if the pistons are to tight, right?

I am not sure Sebastian. You say that you ran the engine at around 2500rpm and only at light load. Unless you went through a process on the road of successive wide open throttle acceleration (typically up to around 4000rpm) followed by snapping the throttle shut (creating a vacuum in the chamber to suck oil up into the rings) I doubt that your rings have even started to bed properly yet. And since you never ran the engine under heavy load I doubt it ran hot enough for the pistons to become tight (that’s assuming there is indeed an issue with the bore dimension). If there was a problem you would see scuff marks on the skirt of the piston. You must remember that a piston is actually tapered in the bore. This is because the crown of the piston gets the hottest and thus expands more than the skirt when up to operating temperature. However, if you bore too small, it is the piston skirt that will pick up scuff marks first.

I did load the rings on the first drive! I drove at seeds of 80mph at points slowing down in gear and back up to speed although i could not give full throttle the car would pick up very well under half throttle.

[Sebastian35]

Geoff it very true whaty you say about the piston skirt! I doubt i can measure it but you can be sure its have had had enough drives to have marked the bore!

Its all to easy to blame myself for boring out to 85mm and putting in pistons! But you have to remember thats what i brought the pistons to do (fit an 85mm bore) and at no point to anyone say otherwise.....

The machine shop did ask for the pistons but i was under the under standing that the aplication was for that said 85mm bore!

Blame is not going to fix anything and we all live and learn! I have been restoring cars for 20 years and this is the first balls up!

I can be if the bores are tight there will be marks!

[GeoffBob]

Geoff I have just checked the Cam timing and there position in relation to TDC are correct! Have not got enough time to check angles today!

OK, that is good to hear. At least we now know that you have no issues with your cam alignment. It doesn’t tell us if you have the correct cam profile, but I’ll leave it at your discretion to decide if and when to measure that. It all comes down to how much trust you are prepared to put in TopEnd. If you believe they sold you the correct cam then you can immediately move on to lifting the head and checking issues related to static CR. If you do, however, have the wrong cam on your engine then you will only ever know by measuring it.

I am pretty sure the problem is with the bottom end, I always have done....

Any particular reason why you think so Sebastian? Something you suspect in particular? I am curious.

I just hope its a piston being too deep and needs shaving!
Then i will try a thicker gasket for the summer...

It’s not unheard of for the crown-height to be out on a piston. It would be a pretty poor show on JE’s part if they did get it wrong though. Once the head is off please measure the protrusion of each piston beyond the deck with a dial gauge. One possible procedure to do this is to raise each piston in the bore until it is flush with the deck. You can check this with a steel rule or engineers square across the block. Now, rest the base of your dial gauge on the crown of the piston (this only works on large enough flat top pistons and may not work with yours) and lower the dial gauge onto the deck so that the nib is depressed by say 5mm or so. Record the value on the gauge. Now, carefully rotate the crank until the piston is displaced to its highest position. You can easily see TDC by watching the dial gauge needle dip to its lowest point. Record the value. The difference between the two values is the protrusion above the deck. Do this for all six cylinders and post the values. We can decide where to take it from there on.

There is one thing for sure as soon as we locate the fault, if being a bore size issue, I will take the block to the Machine shop and let them sort it! No more messing from me I am affraid....I just want to enjoy the summer as all is getting neglected around me as i have been consumed by this thing....

I would honestly suggest getting advice from JE with regards to the bore issue. Tell them honestly ”aI bought six of the following pistons, part number xxxxxxx, I never measured them but I bored to the following dimension xx.xxx mm. Will this be OK or am I screwed once I start to put down some power and the engine gets hot? Only they know how confident they are in their own manufacturing tolerances, so only they can truly tell you if they think you will scuff your pistons.

[GeoffBob]

I did load the rings on the first drive! I drove at speeds of 80mph at points slowing down in gear and back up to speed although i could not give full throttle the car would pick up very well under half throttle.

Duly noted

[Sebastian35]

Off to work now so i will get two hours each do only to mess and give feed back........

[GeoffBob]

[Sebastian35]

Just arrived at work and all I can think about is just buying a set o new pistons to suit the 885 head!
Pistons with a lower useable compression!
Then have the bore work done with pistons in hand.

What do you think of that idea?

[Sebastian35]

Yes this is fist set of forged pistons .

[GeoffBob]

Just arrived at work and all I can think about is just buying a set o new pistons to suit the 885 head!
Pistons with a lower useable compression!
Then have the bore work done with pistons in hand.

What do you think of that idea?

a)Good idea
b)Expensive

Unless your current pistons and bores are damaged I'd start by looking into removing material from the head. As it stands the profile inside the 885 head is not ideally suited to your flat topped pistons in any case. I can't help wondering if it isn't standard practice as part of TopEnd's 2.9 stroker "recipe" to work the head volume? Is a little "head work" not prescribed? You could certainly do with losing 3 to 4 cc of volume by my reckoning.

You’ll still have to strip the engine down. So long as the pistons aren’t scuffed I’d take them along to the engineers and get them measured up and the final 0.0xx bored out the block. That solves that problem. Then we can look at exactly where and what to take out the head, and if necessary, how much to skim off the pistons.

[GeoffBob]

Don’t forget ”¦

Once the head is off please measure the protrusion of each piston beyond the deck with a dial gauge. One possible procedure to do this is to raise each piston in the bore until it is flush with the deck. You can check this with a steel rule or engineers square across the block. Now, rest the base of your dial gauge on the crown of the piston (this only works on large enough flat top pistons and may not work with yours) and lower the dial gauge onto the deck so that the nib is depressed by say 5mm or so. Record the value on the gauge. Now, carefully rotate the crank until the piston is displaced to its highest position. You can easily see TDC by watching the dial gauge needle dip to its lowest point. Record the value. The difference between the two values is the protrusion above the deck. Do this for all six cylinders and post the values. We can decide where to take it from there on.

[GeoffBob]

I just want to enjoy the summer as all is getting neglected around me as i have been consumed by this thing....

i know how that feels.

If your project build doesn't put you in therapy then you aren't trying hard enough

[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. Now that's well back into 95 unleaded territory with no worries about having to add tetraethyl-lead.

Now, at present your compressed volume is 46.5cc (assuming 11.2:1 static CR). To get to 53.3cc you could always look at removing 6.8cc of aluminium (think roughly 7 sugar cubes) from each combustion chamber, but that's one hell of a tall order I wouldn't suggest trying to remove more than 2 to 2.5cc per cylinder. Fortunately there is a goodly chunk on the one side that can come out. Furthermore, each 1mm you take off an 85mm flat-top piston or add to your gasket, will contribute a further 5.7cc to the volume. Simply fitting a 1mm thicker gasket would lower your static CR to 10.1:1, but obviously wouldn't do anything to help your bore problem. If you opted to stick with your flat top pistons you could always look at taking say 2cc out the head and 3cc off the pistons. If you decide to go this route I can describe to you how to do it. You will need to learn how measure chamber volume using a glass pipette filled with white spirit.

Going the new piston route will obviously cost you new pistons. Going the other route you will incur additional machining costs, although, TBH, you can do most of the head work yourself with a grinding tool and a whole lot of patience. One slip onto a valve seat though and your work is in vain. Either way you choose I’d suggest sorting your bore out.

[Sebastian35]

Even if i sort out the bore i am still left with pistons i did not want, as my original order was for a dome top piston.

It anyone wants the flat top pistons that I'm about to pull out please message me!

I will make sure the new pistons get the dome I asked for in the first ......

I will post my results when finished.....

[ezagood]

And some seriously good looking pistons you have there too Ezagood! So I take it the change in CR is down entirely to the change in stroke and slightly bigger bore? 10:1 should work quite nicely.

exactly that sir .

Want me to do a pressure calculation for you Ezagood? We could wager 1£ as to whether or not I'll be with within 10psi of your measured value. I'll wager another 1£ on top of that, that you'll win the first £

i have just looked through your build thread. im sure you have better things to do but hey, go for it.

[ezagood]

you did it while ill was reading hahah.

[e301988325i]

Even if i sort out the bore i am still left with pistons i did not want, as my original order was for a dome top piston.

It anyone wants the flat top pistons that I'm about to pull out please message me!

I will make sure the new pistons get the dome I asked for in the first ......

I will post my results when finished.....

It's the offset bowl that's really important as per ezagoods pistons to suit the offset spark plug.

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.

[ezagood]

order them where i got mine.
Cambridge Motorsport Parts Ltd
Unit 5 Lacre Way
Letchworth
Herts
SG61NR

01462 684300

[GeoffBob]

you did it while ill was reading hahah.

I'm not sure if you will measure the same Ezagood as I am not sure if your stroke, rod-length, bore and cam are the same as Sebastian's. You're building a 2.7 stroker?

[GeoffBob]

Even if i sort out the bore i am still left with pistons i did not want, as my original order was for a dome top piston.

It anyone wants the flat top pistons that I'm about to pull out please message me!

I will make sure the new pistons get the dome I asked for in the first ......

I will post my results when finished.....

Fair enough. If it's domed pistons you were after in the first place then it's a pretty poor shown on TopEnd's part to have sent you flat-top pistons and then simply told you "that's the way we do it".