Compression Questions

[Basketcase2156]

I have been suspecting some compression issues with the bike.

Reasons:

One: I have to put in about and 1/8 of a quart of oil every 300ish miles. I use Rottela T 15W-40.

Two: When I rebuilt the motor It only had 3600 original miles so I really only changed all the gaskets. In the process I measured everthing out and it was fine. The cylinders showed no signs of wear and the rings where great. But.... When I was putting the cylinders back on I screwed up number 3's rings so I put a new set in.

Three: I get leakage out of the valve cover and breather. See following picture.





Four: The crank case breather mists the motor with the hose off. See photo.



At least I think that's a breather seems kind of small but I can't find any reference to it in the shop manual. Can someone tell me for sure?

So I checked the compression. 1= 70PSI 2= 65PSI 3= 60PSI(replaced rings about 1500 mile ago) 4= 70PSI. In my experiance your mostly looking to see if they are the same and they seem close enough.

Lastly the plugs look like this:

Number one:



2-3



I know it runs lean on idle. I need to replace the boots and O-rings. I mostly concerned about what number one looks like.

Any ideas would be appreciated.

[mike_of_bbg]

One: I have to put in about and 1/8 of a quart of oil every 300ish miles. I use Rottela T 15W-40.

That's about a quart per oil change. Not that bad for an air-cooled engine.

Two: When I rebuilt the motor It only had 3600 original miles so I really only changed all the gaskets. In the process I measured everthing out and it was fine. The cylinders showed no signs of wear and the rings where great. But.... When I was putting the cylinders back on I screwed up number 3's rings so I put a new set in.

Did you hone the cylinder when you put in new rings? I see below that your #3 cylinder has the lowest compression.

So I checked the compression. 1= 70PSI 2= 65PSI 3= 60PSI(replaced rings about 1500 mile ago) 4= 70PSI. In my experiance your mostly looking to see if they are the same and they seem close enough.

Were those numbers taken with a hot motor and wide open throttle? Yes, you want them to be close but you also want them to be over 100PSI, which they should be HOT+WOT.

Have you adjusted your valves recently? Maybe it's time and also check your cam timing.

[mike_of_bbg]

Also, you should check the compression wet: put in ONE TEA spoon of oil in each cylinder (still hot) before you test it and re-run. See how much your compression increases.

[Nessism]

Did you replace the valve stem seals while the head was off? How long since the last valve adjustment?

[gearhead13]

Thats quite low compression for a rebuid, I am getting 150+ psi on all cylinders.
I have no hose attatched to the valve cover at all and no oil spray comes out.

[Basketcase2156]

That's about a quart per oil change. Not that bad for an air-cooled engine.



Did you hone the cylinder when you put in new rings? I see below that your #3 cylinder has the lowest compression.



Were those numbers taken with a hot motor and wide open throttle? Yes, you want them to be close but you also want them to be over 100PSI, which they should be HOT+WOT.

Have you adjusted your valves recently? Maybe it's time and also check your cam timing.

No I didn't hone the cylinder. I was so mad at the rings it didn't come to mind.

The motor was hot and the throttle was closed when I did the compression test. Never thought about it but WOT makes sense.

The valves were done with the motor and the timing is good. I spent extra time double checking both of those.

I'll do the compression test again WOT and hot when I get home from work tomorrow.

[Basketcase2156]

Did you replace the valve stem seals while the head was off? How long since the last valve adjustment?

No with such low mileage couldn't see pulling the valves.

Thats quite low compression for a rebuid, I am getting 150+ psi on all cylinders.
I have no hose attatched to the valve cover at all and no oil spray comes out.

I wonder if your bikes have a different compression ratios? I assume the EZ would be the best comparison. My book is at work I'll tell you tomorrow what mine is. I hear a little oil out of the breather is OK but not much. I only get a little into the air-box. It all seems to come from the breather cover gasket and I noticed some from what bikebandit calls the "plug bevel gear". I don't know what that is. It is above the clutch/tranny and below the carbs. Pull the hose off and you get oil on the motor. Not enough to notice but over time it builds up. (couple hundred miles) I've seen blow-by before and this looks kinda like it but then when you feel how much air actually comes out it doesn't seem like too much. But then this is the first air cooled motor I've worked on. If the oil consumption is not bad then maybe the breather gasket is just messed up somehow and I'm being overly paranoid.

[gearhead13]

I recently pulled the jugs off mine to replace the base gasket, and I did a light hone and used the old rings. It has 10.5-1 pistons in it now, but I was getting near 150 with the stock pistons.
Your compression should jump 30psi+ or so with the throttle wide open, I would think.

[BigD_83]

I was testing my compression one day and forgot to go WOT. I read 70PSI. After thinking about what I had done, I redid it properly and got the reading back up to 160...I nearly had a heart attack thinking I had just blown the head gasket big time.

[Nessism]

No with such low mileage couldn't see pulling the valves.

Big gamble to not replace those 30 year old rubber seals. They cost all of about $3 each.

[Basketcase2156]

Took me a bit to test it again. The compression tester I was using didn't have a valve in it so I bought a new one. HOT+WOT= #1 110PSI #2 100PSI #3 90PSI #4 110PSI. #3 scares me. The book says 114-170PSI on a fresh rebuild. 100PSI limit and 28PSI difference.

[Basketcase2156]

#3 with a little oil 95PSI, not much change. Valve seat issue maybe?

[tkent02]

#3 with a little oil 95PSI, not much change. Valve seat issue maybe?

Did you adjust the valve clearances correctly?

[BigD_83]

Are you setup to do a leakdown test?

[Basketcase2156]

Yes, I did the Valve clearances correctly, checked and double checked. No, I don't have a set up to do a leak down test.