M38 engine stroke length

Claudio · Post by **Claudio** » Wed Apr 18, 2012 6:40 pm

Hi everybody,
Since I bought my 52M38 I had the feeling that engine wasn't that powerful, when compared to my 42MB, both having quite same engines. Besides that, the M38 frequently boiled water out of the radiator, specially and obviously when driving uphill in our hot summer in Brazil.
Now I decided to find out what may be going wrong, so when disassembling the engine head, I found out that the piston, when reaching the top dead center, was not alligned to the engine block surface. I measured the small and missing stroke length (2,2 mm), just as thick as one compression ring. Now question, what is the reason for such a lack of 2,2mm in the stroke length? I have measured the length of the piston rods (compared to another Willys 4 cylinder engine piston rod), so as the size of the cylinder...seems to be the same as the ones I picked up for comparision. Any hint?
Is this reduction of stroke length (and so reduction of compression ratio) the reason for such a power loss? heating of the engine?
HELP!!!
Thanks all!
Claudio
Florianopolis, Brazil

Post by **wesk** » Thu Apr 19, 2012 1:54 am

The stroke on the WWII MB, M38 and M38A1 are all the same.

MB/GPW 4 3/8" Compr Ratio 6.48:1

M38 4 3/8" Compr Ratio 6.48:1

M38A1 4 3/8" Compr. Ratio 7.4:1

What you are describing is block deck height. The stroke is determined by the rod's length and the length of the rod throw on the crank. Many engines do not allow their pistons to reach the top of the block deck.

To accurately measure your stroke get the piston located to top dead center using a dial indicator. Mark the cylinder wall and then measure the lowest drop of the piston by rotating the crank until the piston reaches it's lowest point.

BBDE · Post by **BBDE** » Thu Apr 19, 2012 9:08 am

Hi Claudio,

do you have an original head ?
When you have an engine from a Generator set it will have less power because the lower compr ratio.

Frank

Claudio · Post by **Claudio** » Thu Apr 19, 2012 10:26 am

...if I have an original engine head? I think so, but the problem is that there is a small spacing between the piston head (top of the piston) and the surface of the engine block, i.e., 2,2mm. I insist that the piston rod is correct and the piston itself is also correct. A also do not believe there might be any dimensional error of the crankshaft.
I will take up measurements of the piston stroke length, so to ensure the stroke is correct.
I am not willing to remove the crankshaft for a dimensional check, someone could doubt of a wrong crankshaft, but anyway, any deviation on the crankshaft would be very unprobable.

Thanks for your help Wes. By the way, you started meaning the "block deck height", so I still believe this may be the main reason for such a problem. Would you suggest something else about this? are MC blocks different in this sense?.

Any other hint is very welcome guys.

Frank, vielen dank, herzliche Grüsse!!!

Thanks all! all best!!!
Claudio
Florianopolis, Brazil

Claudio · Post by **Claudio** » Thu Apr 19, 2012 12:38 pm

Still about the engine block: the casting number reads 641087-1-W11-AN1-CR-N2.

Thanks
Claudio
Florianopolis, Brazil

°!!!!!º