My 91 GT's engine is rebuilt with new pistons. It started OK with some small vibration at idle. The compression figures of all cylinders are following. Can you comment on these results please.
Thanks for all your help,

 

Look like the difference between the highest and lowest is 1 bar. Tat's withing 10% so I would say it's all fine. Get a leakdown test done and post those figures.

 

Looks like 190psi pretty normal!

 

10% for an engine with new pistons?

My standards are a bit "tighter" than that....I'm hoping everyone's standards are!

I can't think of any reason why an engine with new pistons would be off more than 1%-2%.

 

I think on the holbert engine it was about 180 to 185 on all 8 cylinders. most were 180 or 181. did it a bunch of times.
same thing on my new engine.

I wonder why it would be that different? scratches? how the test was conducted?

 

How many miles on the engine when it was rebuilt?

 

I'm presuming you hand file the rings to get them just right. Perhaps this shop just checked if the gaps were in the range and that's it. Not an ideal way of doing it but a less than 10% variance shouldn't make the engine shake.

 

That looks like a cool piece of kit!

 

How they measured it as well as time between cylinders. Hour or cold? Cylinders honed straight and round? Proper etching of the surface? Valve seats redone? And the list goes on and on. 10% is fine. Do a leak down. More valuable info to be had with that.

 

Thanks for your comments.
Engine was rebuilt with new Porsche oversized pistons, the block was machined, honed and etched with special exposing stone manufactured by KS for alusil blocks. There is no milage on the engine and was tested cold.

 

That's different information.

Run the engine, allow things to break-in (rings seat) and then check it.

Checking compression or leakdown on a brand new, un-run engine is a complete waste of time.

However, I'll stand by my first statement....if you have 10% compression variance on a new broken in engine....someone screwed up.

In this Forum, "rebuilt" is thrown around very loosely. Much of the stuff done doesn't even qualify for "repaired", in my world.

 

How much did that cost? I have a GT engine with 250k miles and am trying to decide how I move forward.

 

Maybe read the user manual for the MotoMeter: http://www.motometer.de/tl_files/mot...sanleitung.pdf

 

You forgot to add 'cold engine.'

I've seen compression numbers change by 10 PSI depending on where in the check order they were. Now I do one side and then re-warm the engine.

 

I thought it was a given that you did a compression test with a warm engine and the throttle wide open.

I typically see 185 psig plus or minus a couple of psi. As engines warm up clearances typically tighten-might explain why engines seize when they overheat!

Regards

Fred