Topic: Oil Compression Testing on a Honda VF500F

[ron.cieri.313]

Hi all...I'm working on restoring a 1986 Honda VF500F.  After rebuilding the engine to replace the countershaft seal (cases have to split on this bike) and restoring numerous other parts and systems, she runs good BUT...I think I made a huge mistake....i.e., not checking for compression prior to my rebuild. 

Current symptoms are she stalls at normal idle RPM...so I have to either keep the choke on (which on this bike is not a closing of the air butterfly but an extra injected stream of fuel) or keep the idle RPM artifiicially high...around 2500 to 3000 RPM to prevent stalling.

I recently woke up to the whole compression thing and test each cylinder (only cold) and found very low compression PSI's...65 - 80 PSI on each cylinder.  I added a teaspoon of oil or so through the spark plug port and re-tested....this test is recommended to see if the rings/piston are the place where compression is being lost...PSI went up 20 - 55 PSI depending on the cylinder...do you you think that's enough to indicate a piston/piston ring issue?

My guess is yes but wanted some experience opinions before operating on this patient again.  The bike definitely had a oil flow problem originally as I found a horribly clogged oil screen filter in the oil pan and scarred valve shaft...also problem why the counter shaft seal failed as I had to replace the countershaft bearing which had gone bad probably due to lack of oil.

Thanks for your help!...Ron

[kirkn]

Ouch!

With all that oil-starvation related damage, I'm surprised you didn't notice any damaged pistons / cylinder walls.  What did you do re: valve lapping?  With a scarred valve, the guides must've been chewed up, too?  Did you do any measuring of the bore / piston?

I'd re-do the compression test.  Motor should be warm and throttle must be wide open, preferably with airbox off and everything.

Because if one of those 65 psi cylinders only came up to 85, that still sounds so low it's surprising it'll even run and you're saying it runs good, except for the idle deal.

Sounds like maybe something else is going on - something in the carbs...

Kirk

[bwaller]

Too bad you're not closer. I have a VF500F engine that I went through and re-ringed, installed a new oil pump, and did a valve job. There are 1000 miles on it since and it's in great condition other than it ruined a cam. I have the heads off it but they are fine, just need a cam and followers replaced.

If you have any way to get it picked up though I'll sell it cheap.

[grcamna2]

bwaller,
     That sounds like a nice engine for ron.cieri.313...is it an 85' or 86' ?

[bwaller]

It's an 85.

[grcamna2]

Sounds Nice for him.