M42 build for E36 Compact

[MrPhatBob]

Although the car came with the M44 engine I found a well priced Z3 M42 engine as I want to see if I can get this thing to rev, I put a 4.3:1 LSD in the car and came to the conclusion that while more power would be good, more revs would be better.

The plans are roughly:

• Wossner 86.5mm 2 ring slipper pistons (S50B32)
• Steel rods - rebushed for 21mm piston pin
• ARP fasteners
• Solid lifters
• Worked head
• Cams TBC
• S50 throttle bodies
• TTV 5kg flywheel

I'm keeping the stock stroke, so with an over square engine using light components I should have a light revvy engine.

Checking the S50 ITBs fitment:


Into the hot wash:


Drill and tap the oil gallery bung:


Trial fit an M14 threaded bung:


Cleaning the oil way galleries:



The questions I have are really surrounding the choice of pistons and rods, I'm fairly happy with the Wossner pistons because they have a lot in common with S42 pistons, but the rods are a bit of an issue, I've looked at Eagle, but they state that they weigh 540gm I weighed the stock M42 rods and they come in at 547.1gm, so thats not significant enough to warrant purchase.  ZRP rods claim to be 483gm, but what other options are there?

[thebrelon]

M44 stock rods are said to be 100g lighter than early M42, but as your are coming from a Z3 they should be of the light type.
if somebody could weight early M42 rods we could get direct comparison.

[MrPhatBob]

According to Metric Mechanic's M42 booklet the early M42 rods are 610gm, so these are the light type.  This M42 version has piston squirters, chain upgrade and all that sort of good stuff.
The weight of the ZRP rods is good, the Metric Mechanic I beam rods are said to be 475gm but are 2mm shorter, with the low compression height (around -0.5mm) of the piston I'm going to run out of chain tension if I deck the block by that amount.

I'm being challenged on my rod choice by the people who own the workshop I'm lucky enough to be using, they build high-end race and classic engines so use known top name manufacturers
(like this hand finished piston on a Pankl rod )

Their concern is that many of these "new" budget brands is that they may be a costly mistake - buy cheap buy twice.

[jrw21]

I weighed each rod I was anticipating on using: (the weights are with bearings). Metric mechanic 610 gram is weighing the ROD only, not the bearings or the bolts.

[MrPhatBob]

Good point on adding the bearings into the mix.  The engine builders reckon that a good few grams could come off the standard rod with some judicious use of the grinder, removing the casting marks down the side, rounding the shoulders on the big end, but its not going to lose a massive amount of mass.

[wazzu70]

Pauter also makes a 140mm rod.

The lower end rods arent horrible, you just have to double check the machining. Make sure your big and small ends are round and the correct diameter. Thats usually the issue with them is lack of machining quality/QA.

Most of the cheapo rods are only 135mm anyway which wont work for you.

[MrPhatBob]

Well these are the ZRP rods: http://www.forged-pistons.co.uk/webshop/zrp-h-beam-forged-connecting-rods/b-m-w/bmw-m42-m44-r-bmw-002h/ I'd put them at "mid-price" range.

[Warsteiner]

Not sure what length rod you're looking for but if you need to drop down to help with your calculations then you can use an aftermarket equivalent of the Honda 1.8L VTEC B18C (GSR) 138mm rod. You're also ready to go since the S50B32 piston already has the 21mm wrist pin.

Cheers,
~Ralph

[MrPhatBob]

Thanks Ralf, I'd seen a mention of that type of rod being used - the problem is that it will mean a 1.95mm block skim

• M42 Rod length = 139.9 M42 Piston compression height = 31.65 (139.9 + 31.65 = 171.55)
• B18 Rod length = 138 S50B32 Piston compression height = 31.6 (138 + 31.6 = 169.5)

I don't know how this will effect the timing chain at this stage, it doesn't *seem* to be much, but  I'll talk to the machinist tomorrow and see what he reckons.
Getting a rod rebushed down to 21mm will not be too great an issue if I stick with M4x rods.

[Warsteiner]

MrPhatBob.....please list  your complete build. Your numbers seem slightly off.

S50B30 US  32.8mm CH/86mm bore

S52B32 US  31.0mm CH/86.4mm bore

S50B30 Euro 31.6mm CH/86mm bore

S50B32 Euro 32.3mm CH/86.4mm bore

Position = (Stroke/2) - rod length - compression height
212.15mm = (81mm/2) + 140mm + 32.3mm
212.15 = 40.5 + 140 + 32.3
212.15 = 212.8
This tells you that the piston needs to be shaved .65mm to return back to stock location. But what will your compression be??
Euro 3.2L pistons gave a 11.3:1 compression

Just food for thought....

HTH
Cheers,
~Ralph

[MrPhatBob]

The 31.6mm compression height is what Wossner state for their 2 ring slipper piston I think that this is the difference in your and my figures?

[Warsteiner]

Ok so that puts you in a position for the math again..... You're going to come up slightly short.

212.15mm = (81mm/2) + 140mm + 31.6mm
212.15 = 40.5 + 140 + 31.6
212.15 = 212.10
So you're .05mm short using that piston. If you had the stock 3.2L Euro 32.3mm piston you'd be ok

Not sure how being only .05mm short will effect the chamber in the head for combustion. I'm not that technical. You will have to ask your people you're working with or maybe someone on the list will chime in. You are really close to making it work. I'm still not sure that decking the block is the answer but ask around.

Cheers,
~Ralph

[MrPhatBob]

Yep 0.5mm short using stock rods, 1.9mm short using Honda B18 rods.

Decking the block is something that will be happening anyway, they use a flat bed grinder to give the flattest of flat surfaces, and usually use a thicker MLS gasket to make the difference.  We'll see about the possible depths later today.

[MrPhatBob]

Nothing amazing to report on yesterday's work as the job was all about measuring ports and modelling them in a CAD Package, so that we can get the head sent off to Jondel Motorsport for port work while we're machining up the


The ports and throttle bodies have been measured and modeled in a CAD package. The surfaces were then printed onto A3 paper, the holes punched, and the paper copy checked for dimensional accuracy.

The cut out hole on the left is the profile of the port, on the right is the profile of the throttle body.

We can now machine the adaptor plate from the measurements.  If you look closely the ports are about 1.1mm larger than the throttle body, it should be possible to blend this nicely with about 25mm thick aluminium.

I've not done any accurate measuring for about 5 years so I was quite happy with the end result - although it needed a significant amount of input from the Precision engineer who was helping me 

[wazzu70]

From the factory the inlet manifold ports are usually slightly undersized. This is to eliminate the chance of manufacturing variation making the ports line up poorly.

If you think about direction of flow, its a lot better for the inlet manifold port to be unobstructed by the head. If the inlet manifold port was the same size or slightly bigger than the head port, you would have a small lip...and that would cause some issues!

Still, since you know what head and what inlet manifold you will use...you can match them with higher confidence!