M42 Rotrex (for sale!) + track build

[rix313]

Was defo aluminium but I will use a minimum of 10mm and prob 12 where I can.

Hey Rich,

I'd say at least 8mm thick ali for the brackets, well braced with say 6+mm thick material.

The gearbox was such a bitch to fit can't face doing it again if you could Ash that'd be brill but I don't know why it's so impossible to find a prop shaft this is a standard Getrag 240 box.

Here is the back of the 'M42' box:




Here is the back of the 'M40' box (which so I've been told came off of an M42):




Neil from A1 BMW is on the hunt for a prop for me.

[hoshy]

weird but still i'd think there's enough adjustability in the prop so cope with that ?

[appletree]

What prop are you after? Ive got a spare IS one goin...

[rix313]

If it's 665 from here to here:



Then I'll take it lol. The lower one is my iS one and the top one which is shorter was from a 316i.


The adjustment in my prop is on the differential side of the bearing not the gearbox side and the slots on the bearing don't allow it to move far enough forward.

Would need a whole one though to save having to rebalance etc.

[hoshy]

I've got half a prop in the garden too but I think it's the diff side - will check and let you know.

[rix313]

Small update if any one's interested

The Main Man Matt came over the other evening with his big tool and gave me a hand fitting the spacer for my crank pulley wheel. So just need to get down the local fixings store and get some bolts that're the right length and get the 6v pulley fitted!

I've now started making my plywood model of the charger bracket, it is going to differ slightly from the cardboard beast previously pictured. Principles of it will be the same but with some bits shuffled about. I am currently in talks with a design company who will be making it for me and we've decided to make the bracket a bolt together job. Matt brought up the fact that he didn't weld his due to distortion which got me thinking, then the engineer I have been talking to also recommended it be a bolt together system so that is the way we're going

So I'm aiming to have a working charger bracket model by the end of next week which will be followed by a 'life like' 3D model provided by the design company and then from that the real thing all being well! I don't have a date that I want it to be bolted to the engine to by but it's going to be as fast as time allows

[GeoffBob]

Matt came over the other evening with his big tool...

Matt you stud.

....we've decided to make the bracket a bolt together job. Matt brought up the fact that he didn't weld his due to distortion which got me thinking ...

Personally (only my opinion) but I'd weld it and then reface/skim the three sides (orthoganal to each other) on a mill. No matter what bolts you put in, the weak point will be the threads tapped into the alu plates.

[rix313]

Well had it running for 35 minutes today while I fafed about with my bracket then I revved it up high and it made a clunking noise for about 5 or so seconds then stalled.

It now wont start. Turns over fine with no apparent nasty noises, nothing leaking or dripping. Oil pressure warning light goes out during cranking so there is pressure. There were no big bangs or puffs of smoked from any where. Litteraly made this rattling light clunking noise then proceeded to stall and die. Temp needle didn't go over half the entire time I was running it (I was checking it lots). Quick peak in the rocker through the filler cap doesn't appear to have any nasty bits in it.

Guess I need to get the timing case off and see whats happened Juast as I was starting to get some where

[appletree]

Shame rich, wonder what the noise could be. Could it be a damaged tensioner/guide.

As geoff said weld it and machine would be best, but the bolt it method in my oppion would be the next best thing, i used the intermediate plate in mine to make sure i had 20mm of steel to screw into.

How much are you looking at for your bracket? Id be intrested in getting my bracket remade in alloy depending on price. May have found you a gas pully to

[magpie]

i hope this latest set back isn't a big one.

seems to me your car has fuel pump prob same as mine had.
i got another pump and still the same so i put direct 12v to it to test and it's fine


so next door to you fuel pump relay is an unused relay block nearest the fuse box.
i took a live from here and ran it through the bulk head back to the pump.adding an inline fuse under the bonnet to it.it stays live when cranking so car starts and runs fine now.

[rix313]

Was good to see your car at the weekend Matt looked great

I remember you showing me that Mick, I was going to do that but put a switch in the dash and just have it as manual but I unplugged and pluged the pump back in and it was fine after. I have however fitted a small bulb to the dash which is connected to the fuel pump so I know if it's on or not .

I've taken the rocker cover off the engine and had a gander, the cam's are in a uniformed state I.E. they aren't all over the place they look fine, I know it's not much but it's a start. After our chat at the weekend Matt, I'm wandering if it is the tensioner and the rattling was the chain loose due to the tensioner being stuck out when I let the engine idle.

[rix313]

I'm still here

Soo, the most progress I've had during my peaceful silence is put the wheels on the car because I was fed up of it being on axel stands for so long.

Engine still doesn't work but going to tackle it again Sunday morning for a few hours see what I can do.

Current plan stands to see if I can get the engine running again as it is so it can purr again; then, rip the thing out and rebuild it Going to do a 'freshen up' rebuild and replace every single gasket and seal and clean the hell out of the manky oil covered casings.

Geoff is also helping me look for some pistons to lower the CR while the engine is in bits so I can get some more safer power from the engine. We shall see what happens

[appletree]

Think you can use evo 7 or a vaux calibera turbo XE??? pistons so ive read on the m42 club

[GeoffBob]

Rich,

Following the standard method for calculating the CR of an engine:

CR=(V_stroke + V_squish)/V_squish

where "V_stroke" is the volume of that portion of the combustion chamber volume occupied by the piston stroke (from TDC to BDC), and "V_squish" is the remainder of the chamber volume above the piston at TDC.

Since the volume of a cylinder is:

V=h*pi*(r^2)

where h and r are the height and radius of the cylinder respectively, then, for your M42 engine:

V_stroke=81mm*pi*((84mm/2)^2)=448883mm^3, or 448.9cc.

A simple check of this number is that 4*448.9cc=1795.6cc or roughly 1800cc.

Now, if the CR of the standard M42 is 10.1 (assuming stock gasket) then (from the first equation)

V_squish=V_stroke/(CR-1)=448.9cc/9.1=49.3cc

Now, if we choose to lower the compression ratio say CR=8.5 then, as before

V_squish=V_stroke/(CR-1)=448.9cc/7.5=59.9cc.

What that means is that to lower the CR from 10.1 down to 8.5 we need to increase the "squish" volume above the piston from 49.3cc up to 59.9cc. Thats a difference of:

59.9cc - 49.3cc = 10.6cc.

One way to do this is to lower the height of the piston crown, and since the bore has a diameter of 84mm this equates to a change in crown height of 1.91mm.

I would therefore suggest that you seek out a piston with similar dimensions to an M42 piston (as discussed in my e-mail), but with the crown of the piston 1.9mm closer to the centre of the gudgeon pin. I'd suggest that you start with the two pistons that Matt recommended - get data on them, measure them up etc. If you can't find a piston that is exactly 1.9mm shorter than the M42 piston (from crown to centre of the pin) don't worry, there may be some room for machining and fiddling with gaskets later on. This is the figure that you are aiming for though to get a CR of 8.5.

Also, try post up a pic of the crown of an M42 piston for me. If there are any valve pockets in the crown I will need to incorporate those into the above calculations. But before we go that far you need to get your search underway.

[GeoffBob]

Rich, also check out the 1mm oversize (84mm diameter) pistons for the Nissan CA18DET. 20mm gudgeon pin, no dome or dish, and a compression height of 29.75mm. Of course if you want to rebore the engine, maybe we should be looking at 84.5mm diameter pistons.

Anyone know the gudgeon pin diameter and compression height of the standard M42 pistons? Matt ???

[rix313]

Right, From what I can tell from the below image, if the top number (KH, Krown Height spelt funny?) is the compression height then it's 31.65mm. Taking the 1.9mm from this makes 29.75mm as you stated above. Looks like the pin is 22mm too? There is a slight dish to the crown of the piston too not sure how large though.




EDIT: here's the key:
KH=compression height
VT=valve recess depth
MT=combustion chamber depth
Mdiam=combustion chamber diameter
GL= total lenght

[GeoffBob]

Aaaaargh, then the CA18DET piston won't work. Bugger! CA18DET has a 20mm gudgeon pin. Pity, otherwise that oversize CA18DET piston had exactly the compression height you needed!

Oh well, keep looking.

Can you get data on those other two Matt mentioned Rich?

[GeoffBob]

Hey, that pic of your says that the M42 is a 1796cc engine.

I got 1795.6cc in my calculations above

My head gets bigger by the minute

[GeoffBob]

OK, found some info on the Evo pistons Matt mentioned. Looks like the 2.3litre stroker piston is required otherwise the piston is just too tall.

Wiseco do an 85mm diameter forged piston with a 22mm pin and 28.7mm compression height for the Mitsubishi 4G63 engine stroked to 2.3 litre. You'd have to overbore your M42 by 1mm for this to work. Not sure that Wiseco pistons are what you after though Rich. Damn, I'm sure there must be something in the AE catalogue that will do for you.

[rix313]

I was just looking at the very same thing CP pistons do a 28.8 one too. Not having much luck on finding the spec for the standard pistons though.

The Vauxhall pistons all seem to be 86mm upwards.

How long does a rebore take? I have free run of the engine shop I'm going to be using ya see so can do it while I'm there.

[GeoffBob]

Not more than an hour, but if you haven't done one before, get someone to show you the ropes. One slip and its goodbye M42

A rebore will freshen your block up nicely. Will give you a clean slate to start from. Get someone to show you how to check your crank for roundness. If the journals have ovalled you'll want to skim them and fit oversize bearings. And while she's open, check the oil pump. I hate to see overhauled engines foiled due to the re-use of mangy old components.

And dude, if this is your first engine rebuild then get yourself the book "How to Rebuild Any Automotive Engine" by Barry Kluczyk from http://www.cartechbooks.com . What you will learn from this project will stand you in good stead for the rest of your career. You can't beat learning to rebuild an engine in a free workshop!!

Has anyone got an M42 standing open please !!!!
I really need to know the dimensions of the dish in the top of the M42 pistons. Can't make head nor tail of that pic you posted Rich. Only some of those dims make sense to me.

Once I have those dimensions I can calculate exactly what your engines CR will be with the new pistons.

[rix313]

Looks like I owe my left nut to Geoff (although I hope he doesn't accept as it'd hurt ).

Turns out M54B30 pistons are 84mm with 22mm gudgeon pin and have a crown height of 28.32mm. They're also available in an 'over bore' size which is +0.25 larger. MAHLE carry them in stock and they're £96.50 with rings and pin. just need to check a few more things.

I'm not sure when it is I'm going to do it but armed with the info etc I can now put a plan together.

I am going to see if I can get this engine running (and thanks to sir legend named above the problem may have been pin pointed but we shall see), charger bracket designed and made then engine rebuild.

On a 5 minute high.

[GeoffBob]

Very kind of you to offer Rich but you can keep your nuts to yourself Will kindly accept a pint or two next time I'm back in town though . As I said in my mail though, we need to check out the details of those M54 pistons before getting too excited. I really need to see the details of the valve cut-outs, so if anyone reading this has the pistons from an M54B30 lying around (don't we all just have a few of these engines hanging in the wings) then please oblige us with a pic or two and some dimensions. For the life of me I can't make head nor tail of the data on the Mahle site here (enter "M54B30" where it says "Designation" and click start search) because I don't know what the German abbreviations stand for. Anyone ??

[Gunni]

That picture posted is supposed to be much larger and you can then see what the markings mean if I recall .. But the program that picture comes from definetely has the information.


And I think this has some of the explanations
http://www.bmwccn.no/rogaland/Mahle_m20.html

[GeoffBob]

Thanks Gunni, you've been a big help! I have now been able to decipher what some of those measurements mean - and sadly I now have more questions than I do answers

First of all, the M54B30 piston crown sits a lot lower in the block than the M42B18 piston. This would tend to give the impression that this immediately results in a drop in the CR and heypresto - problem solved. Unfortunately the M42 piston has a hemispherical bowl in the top of it that is a whole 4.5mm deep! That means that a goodly part of the squish volume lives in this bowl, with the remainder in the head. On the other hand, the M54 piston (albeit a whole 3.33mm shorter, from the crown to the gudgeon pin) has a 0.76mm dome on top of the crown.

Now, while the mahle site provides the basic height or depth of the various features of each piston, it does not quantify the actually volume displaced by these features, and that's what I need to know in order to say what the CR will be with an M54 piston in place of an M42.

If I had one of each piston in front of me right now, here's what I'd do:
I'd clean up the inside of a bit of old pipe on a lathe to exactly 84mm inside diameter. I'd then coat the edge of each piston with grease or vasceline (to lubriate and seal) and slide them in (one at a time) to a specified depth (so that their crowns sit at the same height during each test). I would then slowly fill up the volume in the top of the pipe (above each crown) with white spirit dispenced from graduated pipette. While this wouldn't tell me anything about the absolute volume of each pistons squish volume, the difference between the two numbers would be the difference in the actual squish volume between the two pistons, and that's really what we need to know Rich!

We really need to get this info in order to make an educated decision as to whether the M54 pistons will work in your application.

[MarkT]

Interesting reading about the vauxhall LET pistons. Is there any reason why they couldn't be used? What compression ratio's given on a standard engine, head gasket etc?

[rix313]

Small note:

I got my new injectors. Got bored of getting ones that didn't fit so got some cream top K-series ones All ultrasonicaly cleaned and tested (by none other than Injectortune). Also found a FPR take off thingy for my remote one:

[GeoffBob]

Right then, using both the Mahle data as well as the measurements you e-mailed me Rich I have been able to calculate the CR of an M42B18 fitted with pistons from an M54B30.

Starting with the M42 pistons I determined the hemispherical "bowl" in the top of the M42 piston to have a volume of 8.707cc (you'd better check this using the method of Vaseline, white-spirit and "bit-o-Perspex-with-hole" in case I got this wrong! After all, its your engine that could blow up and my calculator feels no grief or sympathy )

Moving on, at a CR of 10:1 the M42B18 (with stock gasket) has a squish volume of 49.88cc (I determined this before, see one of my earlier posts). Subtracting the "bowl" volume in the top of the piston this leaves 41.173cc of volume actually tucked up in the head (around the valves and the gasket).

Now, a piston from a M54B30 has a crown height 3.33mm lower than the M42B18 piston. Taking into account the 2mmx0.75mm chamfer around the edge of the M54 piston, then the extra 3.3mm above the crown contributes 18.647cc of additional volume.

Thus, the new CR (with the M54B30 piston) is =

(448.88+41.173+18.647)
------------------------------- = 8.5
(41.173+18.647)

Spot on what we wanted I'd say

Rich, I think you can go ahead and order a set of those M54B30 pistons. You'll need to check though that the piston skirt doesn't catch on anything (on the crank counter-weights for example). If they do, a little machining will be required. You may also have to contemplate having your crank assembly rebalanced now that you are changing the mass of your pistons, but we can discuss this another time.

Take note, however, that my calculations assume that the valve cut-outs in both the M54 and M42 piston have identical volume. While you gave me some information on the M54 valve cut-outs, you gave me none on the M42 cut-outs, so I assumed they were the same and hoped for the best. You may recall I asked you to measure up a set of M42 pistons as well?

[rix313]

Thanks for that Geoff

Once I've decided which engine to work with I'll take it apart and get some measurements from the head and the pistons as requested.

Interesting reading about the vauxhall LET pistons. Is there any reason why they couldn't be used? What compression ratio's given on a standard engine, head gasket etc?

Best place to ask Mark is prob on M42 club

[tim_s]

d'oh, shame I missed this, could have saved you a load of work!
for the 330 pistons, £95 is EACH from what I remember -they're not cheap.
They have small reliefs and are flat pistons. I used to have a set kicking around in my garage, might still have them actually! They're a modern piston and perhaps not the best choice for a tubby m42. there are a lot of factors to consider.
On the m54 ones the top ring is very close to the piston crown as per lots of modern pistons and like all modern BMs they run tight piston-bore clearance. For a turbo application these make much less sense imo than a nice set of forged pistons with a much looser clearance, bigger top ring to crown distance and a big bowl. In terms of managing temperature, improving atomization etc, custom forged pistons will be way better.

[rix313]

It's a question of budget for me Tim. I didn't think £95 for brand new piston with rings and pin was too bad. I borrowed one off of a freind of min who's building a M50b30 to take measurements from.

The way I look at it is I could buy forged but the return on investment for £600 pistons won't be so fantastic and wont use them to their full potential unless I proceed to spend yet more money upgrading the other parts. Seems a little like having Miss USA as your wife and then going abstinent, you got it but you aren't using it properly.

What do you mean by 'tubby'?

[tim_s]

edited to turbo, i forgot it was an SC - on reflection FI would have been much better
lol, well, i'm def a build it right, build it once kinda guy! Especially as for me the difference in price is def far too small!

[GeoffBob]

d'oh, shame I missed this, could have saved you a load of work!

Care to identify the exact forged piston you think Rich should be using?

[tim_s]

d'oh, shame I missed this, could have saved you a load of work!

Care to identify the exact forged piston you think Rich should be using?

Custom - any brand, I'm not particularly snobbish about it. Was that intended to be rude?

[GeoffBob]

d'oh, shame I missed this, could have saved you a load of work!

Care to identify the exact forged piston you think Rich should be using?

Custom - any brand, I'm not particularly snobbish about it. Was that intended to be rude?

Not at all rude. I just think it would be really helpful if you would be so kind as to identify that forged piston you mentioned. God knows how many pages of this thread have been dedicated to finding it. Ever bought a forged piston for a M42B18 as I'd be really interested to hear what brand you bought? Afterall, you said you could have saved Rich a load of work, and I for one would like to know who makes a forged piston for the M42B18 (short of going for a 2mm rebore to fit a forged Jap or Vauxhall piston)