Frankstein's engine (M42/M44/S50)

[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

[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]

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.

[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]

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

[digger]

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

[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.

[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.

[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??

[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

[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

[Ziai]

any updates on a build? :)