Researching m20 engine rebuild & stroking...

[Mops]

Hello guys.

I'm looking for any materials i can find re general engine rebuild/m20 engine rebuild and 2.8 stroker conversion.

I already have megasquirt, but i'm seriously considering total engine rebuild before putting turbo on it.

I'm capable with tools but i never rebuild engine myself, so basically i'm ideally looking for noob DIY step-by-step guide to rebuilding m20 engine (some generic engine rebuild tips are wanted aswell).

Since I'm taking it this far, I decided to stroke it at the same time.

Bacically i'm looking for usefull inks and articles and links to interesting, to-the-point forum thread(s)

As a side note, i'm interested in m20 engine intercompability... i.e. can i use m20b20 camshaft in m20b25 head ? same applies to rockers, etc, etc... again if anybody could point me to the interesting links, it would be great.

Thanks in advance !

[AndyTouring]

If you're going to turbo the motor it really needs a rebuild.

When rebuilding cleanliness, cleanliness, cleanliness is the golden rule. If your work area isn't clean enough for you to have an operation on it isn't clean enough for your rebuild.

Replace all bolts & studs. In fact, replace anything that will be a pain to replace when the engine is back in the car.

Test fit first. Fit one main cap, lightly tighten & check for free movement. Do the same for each main cap. Finally go round torquing them up, checking for binding after each cap.

When fitting the cam use plenty of cam lube.

I'm told the M52 2.8 crank fits in the M20 2.5 block using 320 conrods with no machining req. to the block. If reusing your 325 pistons you'll need to have the bores honed.

When fitting the M52 crank you have to machine down the crank pulley hub to recreate the stepped bit on the M20 crank that the crank oil seal sits on.

Plan a worksheet with each step on it & tick it off when completed. Remember P.P.P.P.P.P. (Perfect Planning Prevents Piss Poor Performance).

Good luck.

[stonesie]

When fitting the cam use plenty of cam lube.

Plan a worksheet with each step on it & tick it off when completed. Remember P.P.P.P.P.P. (Perfect Planning Prevents Piss Poor Performance).

Good luck.

I used to build engines for a living and i cant re-enforce any of andy's points enough.

Grit is the enemy within and can totally destroy a freshly built engine's bearings in seconds, and use plenty of either camlube or another assembly lubricant (engine oil is on the thin side as the engine will be effectivly running dry for a few seconds untill the oil pump has primed and circulated oil throughout the system) and never dry-fit the running surfice of bearing shells.

Also check and re-check the torque settings for every bearing bolt/nut,
After fitting each piston torque the rod down and check that the rod moves side-to-side a little on the crank journal and rotate the crank to check for tight spots, it should be silky smooth

I would use all new bearings and oil seals throughout, and be carful with the oil seals to check they are seated properly and the lips are not folded back, on a teflon seal you only get 1 chance.

Finally i would use a little silicone sealant where the crank main oil seal housing's join the block especially where the sump gasket will sit, one of my mates calles me a bodge artist for this but i prefer ''belt and braces'' to an oil leak anyday.

hope some of that helps.

[Mops]

ah, great help guys....

I'm still trying to source out a 2.7 block...

would it be preferable to get one from wreckers and rebuild, or get one from private sale in going condition ?

how to enforce claeningness ??? latex glower recommended ?

whats the best way to clean the block and parts before stripping them ?

[AndyTouring]

You can buy a 525e short motor & use a 2.0 litre head & intake assembly which is the easiest solution

OR

Use a 525e crank & rods (or 2.0 litre rods, they're the same) in a 2.5 block with (late) 2.5 pistons & head.

If using a 2.5 block the pistons will be 3mm or so down the bore so the block needs shortening which puts the cam timing out so you'll need a vernier sprocket to compensate. I have heard you can get away without maching the block but you'll have a rather low compression - which you'll want if you're going the turbo route.

You can also use the 2.8 crank from the later 24 valve M52 engine with a little machining. Find a one that's died from Nicasil poisoning & it should be cheap enough. This will fit in a 2.5 block without the need for decking but it won't fit the 2.0 block.

It depends on what you have now & where you're starting from.

[Mops]

Thanks for good input. I really appreciate it.

Basically I want the converssino to involve as few purchases as neccesery and as many parst to be reused.

My confusion somes from amount of types of parts. Namely aparently early UK version etas had high compression (11:1), and later ones something like 10.4:1. Aparently US eat's had 9:1 compression. I believe it was all achieved with different pistons. Moreover there was a super eta, and I'm not sure what was different in that one.

I have early UK version 325i, which aparently runs high 9.7:1 compression. I'd like to reuse this head if at all possible.

I could buy a m20b20 head, but AFAIK that head has 80mm bore instead or 84mm, i dont understand how they could possibly fit.

I thought it was as simple as putting I head on E bottom (no block/piston machining), and that will give me 8:0 compresion, which is perfect for turbo setup. Baiscally I read on numeropus forums that I should get away with buying only eta bottom end, which should be pretty cheap.

I'd like to find a document that documents all the different pistons/heada/block types, so i can somehow tell them apart.

[AndyTouring]

The 325 is more efficient than the 2.0 head but really needs the 325 pistons to get the best out of it.

The early (chrome bumper) pistons have a longer skirt which will need machining down or they'll catch the crank web.

Getting the 525e engine is the easiest way although you may end up needing a new set of pistions which adds to the cost.

If your block is in need of a rebore then you could use that with new late (plastic bumper) pistons, a 328/528 crank machined to take the M20 oil seal, your head & intake system to give a good motor.

I have the Total BMW article if you need it. P.M. me your email address & I'll send it on.

[e30_Turbo]

If you're going to turbo the motor it really needs a rebuild..

I disagree totally, a good solid M20 will hold 10psi all day, a complete rebuild should only be required if....it needs it, it's done mega mileage or you have the means/time/energy to do it.

I can list many of us F/I users that are using our original lumps intact and as they were built, to suggest it HAS to be done is madness.

Unless you want to lower the C/R or fit forged parts I'd leave the motor well alone and only fix it when it breaks.

Each motor I swap in costs around £100 so why bother rebuilding one?

Unless your made of money I'd stay stock bottom end and relax knowing if it breaks buy another and off you go.

I'm living breathing proof of this, there isn't many original engine parts left on mine, all swapped as they broke or wore out.

The nature of F/I is too force massive pressure into an engine which stresses most of the system, which is why stock parts are the best way to start with, I would hate to watch my freshly rebuilt engine die at first session cos the fueling or timing was out.

My advise, turbo it, tune it, get it running spot on then if you need to rebuild it, that way you won't be running the risk of another $0000's spent on another rebuild.

I don't disagree at all with any of the engine building tips etc, very good info from a good source as far as I can see but I'd rather risk a stock engine for tuning/setting up than an engine I'd sunk lots of cash into.


IMO that is

[Mops]

Getting the 525e engine is the easiest way although you may end up needing a new set of pistions which adds to the cost.

Thats exacly what I dont understand... why those pistons might be a problem ?

[Mops]

Each motor I swap in costs around £100 so why bother rebuilding one?

Some good points in your post mate. Thats wht I want to get cheap E block, possibly cheap rebuild) and slap my rebuild head onto it. thats it.. i dont want to buy any custom/modified pistons or pay for other machining/fabrication, etc. Bottom ends are quite cheap on wreckers here (thats IF I can find one, but then again, I'm not in rush)

However, consider that here (in New Zealand) E blocks are not very common... in fact pretty rare... I blocks are not common either, generally expensive, but more common than E, with the expeption that I head is expensive, as they crack hence is not many of them.

m20b20 engines are however cheap... and common to find.... then again most heads have worn rockers/cams...

[e30_Turbo]

Why not use the 'i' block with the ETA crank, rods and late b25 pistons?

This should give around 7.9-1 c/r and as easy as you like.

No machining required, just new shells, bolts etc.

You only need to worry about the pistons being correct if your needing the compression (n/a) but the later pistons have a lower pin to crown height so give a little less c/r.

and if you're really lucky to find a forged TD crank then that would be the ultimate choice IMO.

HTH, Mark.

[Mops]

hm..... late I pistons will be hard to find (read expensive)
whats wrong with E pistons under I head ?

m21 TD cranks here in NZ are as rare as rocking horse sh*t, yes I would like one, but good luck finding one here...

[e30_Turbo]

I'm pretty sure that if you use the 'i' block it should be fine, you may have a slightly higher c/r but it should work ok.

I know a man that can confirm this, so I'll ask and return

[AndyTouring]

I disagree totally, a good solid M20 will hold 10psi all day, a complete rebuild should only be required if....it needs it, it's done mega mileage or you have the means/time/energy to do it.

The emphasis being on "good, solid M20". At what point do you deem it not good? All are old engines with 100k - 150k miles or more. There's bound to be wear.

I take your point entirely but stressing an old & very possibly tired motor is going to end in tears sooner or later. Especially since the M20 was never intended for forced induction.

Buying a good 3.0 litre M3 engine with 286bhp all day long would be a better bet in my opinion but they may be in short supply in NZ too.

[mybmw6]

Can you use a 325e bottom end and then use an m20 323i (731 cast head) without having to change the pistons? Every body seems to do it slightly different using different parts and getting other parts modified. What I'd really like to know is the part path that requires the least amount of change? I was told if you use a 325e bottom end, with a 323i head they both have domed pistons and so don't have to be changed. Then using fuel injection from an "I" model and (head has to have some machining done) with valve springs, intake manifold and throttle body from a 325i with 325 cam you've got your stroker. I'm by no means an expert, anyone have any thoughts on the above? Things that are wrong? Would be much appreciated