Hi All!
I am thinking of doing a head swap on a 05 88TC (30K miles) with heads from a 07 96TC. I believe there a few threads on here about that which I have read. But before doing the swap I decided to check the compression.
This is how it was done: removed fuel pump fuse; unplugged coil; removed plugs from both cylinders; attached test gauge one cylinder at a time; cranked engine with throttle wide open; Did not unplug injectors (space too tight and didn’t want to break anything)
Results: both cylinders are around 142 psi. Repeated the test but with some oil in each cylinder and the compression went up to around 160 psi. So, is a 20 psi drop on a 30K mile motor bad? Normal?

Thanks

 

The oil temporarily sealed the rings and the increase in compression would indicate that ring seal is lacking. Adding oil to a cylinder that has good ring seal might increase the compression by 3-5psi but no more. Not good results for a 30K mile motor.

Also, your base compression of 142psi looks a tad low. IIRC, CCP on a stock TC88 should be 150-155. If you are pulling the heads, spend the $300 or so it would take to bore to 95" and fit a set of SE cast flat top pistons. Mill the heads about .030"-.040", reassmble with a .030" head gasket and pick up a set of used SE204 cams on Ebay or a forum and you will be very happy with the results.

 

My 02 Ultra at 92,000 miles has around 140 and I was told that is fine on mine from a certified Harley teck I know real well. How does yours run? If it runs well and does not use much oil I say RUN IT!

Unless they are some fancy heads you are not going to gain that much. Yes 06 up ports are different and better. I did a thread on this but not going to give you a whole lot more unless you do more to your motor.

 

To the OP.

You can run at 142psi, no issues there; however, your static CR should be about 160psi at sea level; 140psi in Denver andsomething in between if you live in between; have to adjust for sea level.

With only 30k miles on the motor, you shouldn't be seeing a 15% variance between a dry compression test and a wet test. The good news is that the compression is consistent between the two cylinders.

Seeing 140psi on a motor with 92K miles rolled up is way different from seeing 140psi on a motor with 30K miles. You can run it like that with no issues; however, I agree with 46u that you are wasting time and money to install the later model heads unless you compliment them with a tighter top end. JMHO.

 

Yes I agree my 02 is no spring chicken but when I am loaded up and between my bike, Hack, gear and me I am pulling at least 1,600 pounds with out a lot of effort. But lord willing and my situration changes I will be building a low to mid torque motor but good chance this will be after I have 100K on it until then she has to keep going as it is the only reliable transportation I have.
Thanks for the input.
Jeff

 

Thanks all for giving your 2 cents....I am going to get the jugs honed and put new rings on, more for peace of mind. As for the heads, they will go on. I am not expecting monster results in output, its more for trying to put a wrench on something. Thanks again

 

Add a set of SE204 cams, set static at 9.6-9.8 and you will be surprised at the results. Of course, you can substitute the cams of your choice for the 204s, just have compression set for the sweet spot for whatever cams you choose. Might as well do it right.