Bad compression... ok, worse compression

Compression tested before and got

60 60 120 120

so i took off the head, cleaned it, lapped the valves, replaced the head gasket and reassembled.

now my compression looks like this

30 60 90 100

Will something please go right?

 

Can you provide some more data on the previous condition and what was done to the BIke? Mileage? Were the valves in spec before the head was removed? What were the symptoms that prompted the compression check in the first place?

 

I picked up the bike from someone who said they had it running great, and it just needed cosmetics.

After removing the carbs, getting the clearances right, and reinstalling the carbs, I just could not get a proper running sync.

All the while, even when it did run, it was all over the map with RPM's. Sometimes idled out, sometimes would rev really high.

Was told to compression test, so we did.

Figured with two adjacent cylinders both at 60, that it was more than likely a head gasket issue, but since the head would be off, i should lap the valves, check that they weren't bent, etc etc.

I did so, reassembled, rechecked the clearances and timing several times.

It ran, so I warmed it up to try to do a running sync, and to make sure the valves settled and anything that may give me a false clearance reading would be worked out... and It actually ran...

ut oh, same revving issues after it was warmed up. And this is all just at idle!!

Let it cool, checked the valve clearances. They are good with the exception of cyl 4 intake is a little over .9, so it's tight, but still at least in running condition.

I decided to do another compression test. Had to buy a tester tonight because last time we did it at mlew's place. Anyways. Tested and here we are.

I was told there were about 26k miles on the engine. Though I realize that it is probably a made up number, now that I've seen all the issues that have come up with this wonderful purchase.

 

Do a wet compression test. NO MORE than a teaspoon of oil in the cylinders. Have at least 2 different gauges, take a couple of readings with each, and compare numbers.

As for the mileage being made up and seeming indicative of th problems arising...I wouldn't be so quick to assume. I have seen several engine over the years that sat neglected and the rings were stuck. Compression will be frightfully low. However, it may not mean the engine is shot. Sometimes you can pour a bit of penetrating fluid in the spark plug holes, and let it sit. I have freed up many engines that were seized as a result. However, you will need to do several quick oil changes to catch all of the rust in the engine/oil, and unfortunately, if the rings were good, and just stuck, the rust will inherently have metal bits and will accelerate the ring and piston bore.

If the wet test shows improved numbers, than stuck, or worn rings are likely. And, the "best" solution is to take the engine down, measure the ring cap, piston bore size, and if lucky, only hone/cross-hatch the bores, and install new rings.

Do a wet test and post results.

 

So... what you're saying is that if I'm lucky, all I will have to do is completely tear down my engine, hone and crosshatch, and install new rings.

yikes.

 

No,what I am saying is you are "lucky" all you will have to do is get the rings to free up. What I said is, (or should have said more clearly) if the wet test shows symptoms of worn/stuck rings, that the best solution is to tear the engine down. And that is if you choose to. You can also shop around for a replacement plant IF you need one. What I meant by being lucky, is that if you do have to tear the engine down the lucky outcome is basically re-ringing the engine. The unlucky outcome obviously would be machining the bores larger, new oversized pistons and rings.

 

how would one "free up" stuck rings?

 

You could try Kroil, or MMO and let it soak for a while.

I can't figure out why you stopped with the head when the compression numbers were so low. When you got the low numbers, didn't you do a wet test to diagnose whether it was rings or valves BEFORE pulling only the head?

You might get lucky and "unstick" the rings. But I kinda doubt it.

At this point you may as well pull it down far enough to properly diagnose the cylinders/pistons/rings; and based on those findings decide if you'd rather fix it or replace the motor.

Since you've already done the head work, if it only needs rings and a hone then it would be worth it.

If the bores are out of spec, then I'd look for a replacement mill.

 

I've tried to keep the work as simple as possible. I know I've said it over and over, but when I got the bike, it was with the understanding that this would most certainly not be needed.

It was important to me because I don't have a proper workspace, and NC weather this summer has proven very few dry days to have a torn down bike just sitting...

So when I have to do things like take head off, I try to keep the work as lean as I can. Basically, I do what I need to, and not much more. That has worked out, just splendidly.

I suppose I learned my lesson. May as well remove the engine, take it down piece by piece. While I'm doing that, I may as well take it down to frame, and go over everything, make it my own. I just wanted to get it running decently.

I'm gonna take it to work, where we have ample room, and I can take some real time and get to know my Maxim.

 

Good philosophy. Take it one step at a time; don't over compensate and tear it too far apart. The next step is just to pull the cylinders off, and then do all sorts of measuring and spec-checking on them and the pistons.

If it really only has around 26K on it, you might just need rings and a hone.

A post-script to this: the bike didn't suddenly lose all compression right after you bought it. Your experience points up the need for doing a compression test when you buy an old bike, so you know what you're buying into.

If you do it right, you'll have a solid machine when you're finished. It just won't be as quick as you originally expected. It never is, BTW.