No Compression

[tkent02]

Did you look in to the spark plug holes as you turn the engine by hand yet?
If it is burnt you should be able to see it. Also a leak down test will tell you more.
It is sounding more like the head will need to come off.

[duaneage]

A compression increase attained using oil or transmission fluid points to the rings, not the valves. The Oil gets into the rings and improves sealing temporarily. If the rings are OK and a valve is bad the oil won't change the compression much (and in this case going from 70 to 90 is not a big jump) since oil won't seal up a bad valve seat well. I think you have a questionable valve.

You could also try and remove the carbs and exhaust to gain access to the valves from behind. With the valve closed (you can tell by piston position and overall timing) you could introduce a small amount of kerosene into the port behind the valve. If it leaks out rather quickly then you know. The exhaust valve is most likely to have damage or carbon build up. If the intake valve is leaking it could be a foreign object is hung up on the seat.

It's not unheard of for debris to get pulled in and captured by a valve, especially when cranking. An engine with a bad spark plug could load the exhaust seat with carbon that causes leaks and poor sealing. Overheating could cause a warped valve or stem, but that is rare. Carbon could build up on the stem and prevent the valve from closing, but after 800 miles that should not be a problem.

The seats won't easily clean themselves. Dis-assembly is usually required.

Solutions range from pulling the head and replacing a valve to attempting to clean the face off with cleaning solutions applied from behind. With winter approaching I would just ride it for now and do a head yank this winter, provided it is just a valve. And you now have a simple way to do a leak down test from behind each valve.

[GSJim69]

I expected that I would need to pull the head.
I am going to ride it until the winter. Then I'll pull the head.
Once it is off should I take it to the machine shop for inspection or is there anything else that I could do to try and improve the situation without machining?

[almarconi]

Once it is off should I take it to the machine shop for inspection or is there anything else that I could do to try and improve the situation without machining?

Once you have the head off, measure..measure..measure. The service manual has an exhaustive explanation of all the head components and their measurements. Once you know then you can make a more educated guess as to what needs to be fixed.

[chef1366]

This can cause a no compression scenario

[almarconi]

This can cause a no compression scenario

I hope thats not the engine you just installed

[duaneage]

This can cause a no compression scenario

You're scaring the man!

It's not going to strand you anywhere, gas mileage might not be that great and it could drink a little oil too, but you have 3 good jugs there so that should be OK. You'll notice it the most at idle but at highway speeds the
"virtual" compression increases because gases are moving a lot faster and even a leaky valve doesn't contain the pressure. The valve would need to be missing to truly affect the engine so badly you could not drive it.

[chef1366]

I hope thats not the engine you just installed

Nope

You're scaring the man!

It's not going to strand you anywhere, gas mileage might not be that great and it could drink a little oil too, but you have 3 good jugs there so that should be OK. You'll notice it the most at idle but at highway speeds the
"virtual" compression increases because gases are moving a lot faster and even a leaky valve doesn't contain the pressure. The valve would need to be missing to truly affect the engine so badly you could not drive it.

Sorry, you're right.

[GSJim69]

My gas milage has been pretty good actually. It's been around 35 city and about 45 riding around at 55. So, I knew it wasn't performing too bad.
Because of the performance, I expected that the compression would have improved over what it was. I was surprised.
I will ride it until I park it for the winter. Then I will pull the head and see what I find.
I'll be asking for suggestions at that time.

[Ponderosa]

Blow down..

Do a blowdown test (differential) on her. Put #1 on TDC and hook up a air hose in your spark plug hole. Put a set amount of pressure to her, you should be able to hear the air leaking by the culprit valve. Not too much pressure now... You can also hook up a pressure gauge to Crankcase vent and see how much blowbye you have...

[supersonictoys]

have you rechecked the valve clearance on that hole since the 800 miles? I have had motors come in with a valve out of adjustment for so long that carbon built up on a valve and seat and when you shim it to spec you are actually shimming it to the carbon. now that the valve is closing further, the carbon hits the head and shatters and goes away, leaving the valve open and the clearance gone. also try re torquing the head. don't remember what hole you said it was but I have seen head gaskets allow compression into the timing chain galley and retorquing brought the compression up 40psi or from a dead miss at idle to a decent running motor. worth a shot

[GSJim69]

have you rechecked the valve clearance on that hole since the 800 miles? I have had motors come in with a valve out of adjustment for so long that carbon built up on a valve and seat and when you shim it to spec you are actually shimming it to the carbon. now that the valve is closing further, the carbon hits the head and shatters and goes away, leaving the valve open and the clearance gone. also try re torquing the head. don't remember what hole you said it was but I have seen head gaskets allow compression into the timing chain galley and retorquing brought the compression up 40psi or from a dead miss at idle to a decent running motor. worth a shot

Hmm! I might give that a try. Got nothing to loose.

[Don-lo]

I agree with supersonic: recheck those shims and retorque the head. The carbon may have been chipped away a little, but I doubt it is mostly gone. Some people have used water injection to clean up the combustion chamber a little, but I would rather pull the head myself.

Another small possibility is a slightly twisted crank, since that cylinder is all by itself and it is the one most likely to have hydraulic gas lockup. If you try and do a leakdown on #1 (setting #4 on TDC) and it blows the piston down, the crank is twisted.

[GSJim69]

I thought that I would give the rest of the story, now that it is back together and running great.
The problem ended up being a bent #1 intake valve. The guide for that valve was cracked also.
So, that valve and guide was replaced. I had a machine shop do a valve job on the rest of the valves while they were at it and machine the head.
Since the engine was tore down that far I decided to hone the cylinders and put in new rings. I had the machine shop hone the cylinders to make sure that it was done right.
There were many difficulties with broken bolts (2 of them) and lots of hours removing gasket material that was harder than the aluminum. I will leave those details out.
Anyway, it is back together and running great. It is still in the break-in stage, but I am real pleased.
Thanks for your help.