Another M44 stroker Build 90mm Crank Question

[mt500ish]

Here is a pic before going to have the keyway cut have used stock diesel crank bolt seemed a bit short so will get the m40 washer and pulley machined a bit so more length in the crank.
The m40 extension cut off the crank and the washer for the pulley will have to drilled out to take the m18 bolt.
Putting engine together to check piston clearance next week.

[mt500ish]

Have put engine together today to find have to DECK THE BLOCK 0.5mm
to make the pistons level with the block.
Some  measurements
86mm pistons s50b30 they are 0.5mm below the block
135mm rods with 21mm pin new bearings
m47n crankshaft 90mm stroke in the block with the pistons is 90.60mm stroke
I have been looking for a long time to get these answers I know it is easy now but my engine builder friend has not done bmw engines before he likes old ford kent ohv and pinto 2.1.
It has been a mission to get this far have had lots of help on the way thatnks for everybodys help

[jerseytim]

mine has a m47 crank and 86mm pistons and had to have bushes in the small ends to take the 18mm pins as the standard rods were used, the block had to be decked but i have no idea how much, once that was done the timing chain also needed work as it was too long. one thing that took time was waiting for the steel head gasket from america because of the bore size. I'm very pleased with the engine, power and how it runs.

[mt500ish]

Thanks for your reply
I have watched your youtube videos nice?
I have had a m44 with light tune cams remap exhaust and 4.5kg flywheel was in a 318i touring so really made e36 318is touring sold it and he crashed it so got it back and put engine in compact was a great car really surprised how the compact was I never thought I would have 1 was more of a bet than a real choice.
I then made 2.8 compact that I drive everyday there is good and bad points for both conversions.
I had 328i touring and sold my m44 compact to my mate and the compact was just as quick round London.
To me the m44 was like a 2 stroke as the m52 is more like a 4 stroke in motorcycle terms.

[Darky]

Hi

The stroke on the tu cranks I believe are 89.6 mm
How are you getting the Pistons 0.5 mm below deck using 140 mm conrods? Most people use the Honda b18c conrods which are 138mm.

Cheers Rohan

[mt500ish]

Sorry for my mistake the conrods are from m52b28 which are 135mm I spoke to MM and they said take the 2.8 apart and use the conrods I did take a good engine apart to find the small ends wristpin gudgeon pin are to big?
I would have had to have the small ends re bushed for the s50b30 because they are 21mm as the m52b28 small ends are 22mm.
To make the bushes and put them in  would have been the same price as having the conrods made with 21mm small ends.

[Darky]

Hi

That makes sense now. But b18c are perfect 138mm 21mm and big end bore is good as well just the width varies from 1 manufactor to another, so you have to be a little careful there.

Cheers

[mt500ish]

You say b18c conrods are 138mm what crank and s50b30 pistons would you use?

[Warsteiner]

mt500ish... You need to do your math. You can make anything fit if you know all your dimensions.

I was the one that introduced the B18C rod to everyone. It was the right choice for the 88mm M47 crank with minimal shaving of the US S50/52 piston. You need to measure your head and block after they have been milled flat and then you figure out your piston height because your rods and crank are not going to change.

Cheers,
~Ralph

[mt500ish]

Quick update done the maths and found that it has 13:1 compression ratio need a head gasket will keep the updates going when I get the headgasket.

[Warsteiner]

  I'm glad you did your math. Now you know where you're at and can get it right. That's going to be a thick cometic gasket. I never had luck with them. If you can change anything else I would start there first. Shave the piston and dish it a little bit more?

Cheers,
~Ralph

[mt500ish]

Been to collect the crank today and it had a bit of a design change

[Darky]

So you made a extension that screws in to the m47tu2 crank and then the keyway is cut in?

[mt500ish]

Yes had an extension made with nut on the end.
Still trying to sort out how much to take off the pistons to change the 13:1 ratio?

[Warsteiner]

mt500ish,

It's more than just how much you need to take off the piston. Is your piston .15mm above the deck? IF not then do your math and get there. Then you'll know how much of the piston needs to come off. If the compression is still too high then you'll need to dish the piston some more and cc it and possibly use a thicker Head Gasket.

I did a quick calc of your math using the 138mm rod for you and it shows a compression height (CH) of 28.15mm. That is the minimum you can go. I'm not sure what that makes the S50B30 piston's crown thickness like, but a brand new piston manufactured at 28.15mm CH is ok. Now it depends on dishing the piston and Head Gasket for compression.
211.5 - 45.5 -137.85 = 28.15

135mm rod: 211.5 - 45.5 -135 = 31    This one may be a better option for you. Talk with your builder friend.

Maybe this will help. Just remember this is for an 88mm crank not your 91mm. Plug in your numbers. Also I just read your post and you already decked the block another .5mm so do all your math a couple of times.

Example:

Stroker Crank 88mm
Combination for Rod and Piston with (M44 1.9L Head Gasket)

Compression Height of Stock US S50 Piston is 32.8mm with Honda 1.8L VTEC B18C (GSR) 138mm rod

Desired Compression Height = Block height - (Stroke/2) - rod length
Desired Compression Height = 212mm - (88mm/2) - ((138mm[Honda rod]-.15mm{protruding out of block}))
Desired Compression Height =      212mm - 44mm - 137.85mm
Desired Compression Height = 30.15mm
The DCH is a desirable height.
30.15mm = 212mm - (88mm/2) - 138mm -.15mm
This tells you that your target compression height is 30.15mm and we have enough meat to shave off 2.65mm from the 32.8mm 
Rod needs small end bushing to be drilled to fit 22mm S50 pin.

To get the right compression of about 10.9:1, I dished the piston about 7cc's and used the M44 HG that was thicker 2.04mm not the 1.74mm.

I hope this helps you. Good Luck. Talk to your builder friend and let him help you with the math part of it. Or find some place online to do the math.

Cheers,
~Ralph