Cylinder Compression

[Heathwerner]

The engine on my new Manx project would not run without backfiring. I checked everything ,timing, adjusted carb, lifters etc... It would idle just fine but would backfire when revved up. So I decided to do a compression check on it and got 75psi on all four cylinders. This seemed very strange to me. I could see if maybe one was at 75psi and the others at different psi such as 100, 120 or even 85 but all four at 75psi !? At this point I pulled the head off of one side and found it looks like it has new rocker assembly and fairly new heads. Then I checked the jug size and it measures 92mm. If I'm not mistaken that would make it an 1835cc. There are no markings on the cylinder head itself. So I'm wondering the previous owner did something wrong when installing the larger pistons and jugs to cause the low compression on all four cylinders. Any ideas would be greatly appreciated.

[Heathwerner]

Well it looks like I've found the problem. Wrong pistons. It appears they put stroker motor pistons in it. The top of the pistons are about a 1/4" from the top of the cylinder and no spacers on the jugs. Looks like I will be ordering new pistons. This how VW projects go especially when you buy from someone you dont know and they bought from somebody they didnt know and what they had done.

[staggerwing]

Good job running down that problem! That car is going to run so good when the right pistons are in there!