Frankstein's engine (M42/M44/S50)

[Ziai]

any updates on a build? :)

[IlovM42]

Quick update. But can't work on the car easily as I work in a foreign country.
I bought 4 high CR forged pistons for s50b30 that will go in the engine when I have time. Will be able to adjust the CR easily by machining à little the centre of the pistons and keeping à good squish area

[digger]

I've heard various opinions on reusing rings. Since they are staying on the same piston and going back in the same hole, any reason not to give it a shot??

Nothing wrong with reusing rings if they are good

[e30sh]

I , it was $200 for new total seal rings. I have a build thread somewhere around here.

I've heard various opinions on reusing rings. Since they are staying on the same piston and going back in the same hole, any reason not to give it a shot??

[benz-tech]

I will give you some advice that I wish I had personally followed when building this engine: Buy once, cry once. Spend the money on correct M44 forged pistons at whatever bore and C/R you want. 86.5mm seems to be the limit of a stock M44 HG and they are under $50. Not sure if you in the US or not but Top End Performance had JE's a reasonable price last year - around $1100 for pistons and rings. Done. I have wasted so much time trying to get my S50(US) pistons down to a usable C/R. They are basically machined flat down to the bottom of the dish but they have no quench area, again to lower the C/R as much as possible. Not ideal, and each time I tried, it was $200 for new total seal rings. I have a build thread somewhere around here.

[IlovM42]

digger it's what i did. i'll do another meaasure before taking it appart again as the crank have to be balanced and i won't be able to work on the engine for a while with work.

[digger]

You need a clear perspex plate with 2 small holes in it a bit of grease and a Burette

[IlovM42]

e30sh i used a seringe to measure. will take something more accurate.

[e30sh]

Not sure if you're using some large beaker or what but you can get a 10 cc medicine dropper at your local pharmacy. People use them for their kids, the pharmacist will just give you one.

You can get ballpark measurements just by sitting the piston on the bench and filling it. I have M 42 and M 44 pistons here. They seem to match the Mahle site.

[IlovM42]

digger yes i saw that method, i will try it to be able to compare and see if i made a mistake somewhere. first i thought that i was loosing fluid trough the pistons rings, second measure i "sealed" the piston with grease but measure did changed.

i did some reserve calculations to see what i need volume wise.

my combustion chamber needs to be 44cc to acheive 12:1 CR

i know the volume in the head (34cc) so between pistons and HG i should have 10cc.

Taking in mind what you told me digger about the squish being more important i calculated the volume 1mm head gasket. logic is no matter how thick the head gasket is, if i keep the squish 1mm this is the interesting volume. for example with a HG thickness of 1.78mm i'll make the piston above block 0.78mm so the piston will reduce the volume of the HG of the same value and we end up with the volume out of 1mm thickness.

if i machine down the piston heigh i will reduce volume but i will be able to adjust.hopefully.

need to sort this out as my track sessions yesterday showed me that the car feel more and more underpower now that it handle quite well.

[digger]

Best way is to drop piston some amount down bore eg 5mm and measure volume to top of block and subtract off the volume of 5mm@bore of 86. That gives the piston cc.

[IlovM42]

hi E30sh.

i did measure the volume at Tdc. bear in mind that i am using euro S50B30 pistons and they do have more dish than the M42/M44 pistons.

I am surpised too with the result knowing that people use S50B30 pistons with M42 crank and it seem to raise the compression a little (maybe they decked the block i don't know.

I'll take some time to do an another measure but i remember that i've done a quick volume measure of the piston alone and found around 12CC

[e30sh]

Have you cc'ed the piston? The Mahle site just gives dimensions for the 286 horse S50. S50 shows 71x3.72.dish. Assuming a 10.7cc head gasket, where are you getting the other 13.3cc? Mahle does show volume for M42 and M44. M42 is 70.2x3.5 at 7.2cc which is close to your dish dimensions before milling.

[digger]

with untouched S50B30 pistons that should give 0.85 above block (83.5/2 + 139.5 + 31.6 = 212.85) and with my pistons skimmed 0.7mm 0.15 above block (83.5/2 + 139.5 + 30.9 = 212.15)

0.85 mm above deck was/is about right with 1.8 gasket.

with 4.3cc pistons i get your CR to be 11.5:1 assuming the pistons CH is 31.6mm and 1.8mm HG which is the upper end of what you want IMO with baby cams. (presumably the 12.5 and 11.5 you refer to is when used on a S50)

[IlovM42]

stock numbers for M44 are as follow:
block height 212mm
stroke 83.5mm
rod 140mm
CH 30.4mm
stock HG thick. 1.8mm
with some math that give 0.15 above block (83.5/2 + 140 + 30.4 = 212.15

my setup
block height 212mm
stroke 83.5mm
rod 139.5mm
CH 31.6mm (right now my pistons are 30.9mm as i removed 0.7mm)

with untouched S50B30 pistons that should give 0.85 above block (83.5/2 + 139.5 + 31.6 = 212.85) and with my pistons skimmed 0.7mm 0.15 above block (83.5/2 + 139.5 + 30.9 = 212.15)

currently head volume have been measured at 34cc (worth doing another measure later, actually will have to after i skimmed the head to remove a scratch that happened during shipping.

measured piston volume with 1.8mm head gasket at TDC is 22cc

V=485.04cc v=22+33=55cc that give CR = (V+v)/v = (485.04+55)/55 =9.81:1

i agree that if i hadn't skimmed the pistons 0.7mm piston + head gasket volume would be smaller as the pistons enter into the HG volume but wouldn't be enough and hard to do an estimation of the volume gained like this.

If i hadn't lowered the small rod bushing i would have an extra 0.5mm above deck to play with. My mistake again to do that before taking measurements

volume of forged pistons is 4.3CC for the 12.5CR i ordered (11.5CR was an optino with volume of 7.3cc)

now did i made a mistake again by ordering the 12.5 and not the 11.5 ones. well possible but again my logic was that i'll be able to increase the volume of the piston by machining it (in a better way than previously) and then lower CR