Thoughts on the compression numbers

[Stefan S]

Looking at buying a new motorcycle engine. The engine is built by a race shop and has 7 race weekends on it. Cylinders were replaced during build

190,183,175,193 Using harbor freight gauge and a battery hooked to a charger.


Based on my research 10% is tolerable so this is right at the limit.

Thoughts?

 

[dcg9381]

I think this is best on a <brand> motorcycle motor forum. 7 weekends being a few runs down the strip or multi-hour races.

Compression is one thing. Leak down - that might tell you more.

Have you seen the rebuild receipt? Know how many "rebuilt" motors I've seen with a few hundred dollars in part receipts? Most of them. Different if you can see all the machine work, balancing, and parts...

 

[larry_g]

I would ask, did you check a second time after putting a bit of oil in the cylinders? I would consider that engine as one needing some work if I were buying it. At minimum add the cost to teardown and inspect.

lg
no neat sig line

 

[Stefan S]

I think this is best on a <brand> motorcycle motor forum. 7 weekends being a few runs down the strip or multi-hour races.

Compression is one thing. Leak down - that might tell you more.

Have you seen the rebuild receipt? Know how many "rebuilt" motors I've seen with a few hundred dollars in part receipts? Most of them. Different if you can see all the machine work, balancing, and parts...

I have seen the build receipt and this is a road racing engine

 

[Stefan S]

I would ask, did you check a second time after putting a bit of oil in the cylinders? I would consider that engine as one needing some work if I were buying it. At minimum add the cost to teardown and inspect.

lg
no neat sig line

It was not repeated but is now pulled and crated

 

[dmdc411]

I'd do a leak down cold and warm. Add a little oil to a low cylinder, see if that corrects the compression. A upper end teardown is needed really with those compression numbers. For regular street driving, it should be fine for a while.

Sent from my SM-G970U using Tapatalk

 

[mjeff87]

Did you test by pulling each plug one by one, or did you pull all of them out and then test? Best to pull all the plugs and block the throttle bodies/carbs wide open. Disable the fuel and spark supply also. I would also X2 on a cold and warm set of tests for comparison sake as well.