Working with a 1987 883 Sportster. Rings were stuck and I worked them free. Compression is at 100 psi with the engine cold. Clymer book I have says 120 psi warm is the minimum. Getting fuel and spark but engine won't run.

I believe the compression is too low and it will probably need a top end rebuild I just want to try and get a few opinions here before I dig into it. I wanted to try and get it running to see what the compression was on a warm engine but it wont fire up. I am going to try some oil in the cylinders and see if that brings the compression up to make sure its the rings.

Before I take the leap and rebuild the top end what other things should I look at first or would I be wasting my time.

thanks

 

First thing is ditch the Clymer manual and get a Harley book. Over the years I have learned that the Clymer manual falls short on some important steps. If the top end needs work go ahead and pull the jugs as well ..

 

When you were freeing up the rings you should have been able to see the cylinder walls and the pistons. How did they look? Did you see any blow-by on the pistons below the rings? If the pistons and walls looked good, you might be able to get away with a new set of rings only. Just make sure you size them properly within spec and cut them only with a good ring cutter. Also make sure you clean the pistons very well where the rings sit.

 

Yes 100 psi is too low and you need to rebuild. Do a leak down test also. You'll probably need to bore oversize, it's typically $65 a cylinder. Metal Layer Gaskets are really worth the extra money.

 

It should still fire off with that compression. You sure you got good fuel, not old. Is it a good strong blue spark? Leak down test will reveal leaky valves or rings.

 

Thanks for the replys. With a little oil in the cylinders compression jumped up to a little over 150 in each.

 

Point to rings then.

 

This.

Sounds like rings are bad.

I'd replace the rings and while you're in there, might as well rebuild the top of the motor.

Oh and make sure that when you freed the rings, they didn't score up the **** out of the cylinder walls.

 

Got it all apart. Both pistons were scored up fairly bad. The top ring in the rear cylinder was stuck completely compressed inside the groove. There may be some scoring in the front cylinder. Once everything is cleaned up I should know more. For some reason there was a ton of rusty dust gathered around the center studs. The two inside studs for the front had a tons and one of the rear cylinder studs was corroded.

I plan on going .10 over on the stock cylinders as long as that is enough.

 

I would then go .10 over also. But before I would check the cylinders out thoroughly and measure the bore at three different locations (top, mid and bottom) with a good bore gauge. It may be better to just take both cylinders to a reputable machine shop and have them look at them and recommend what size up to use. Let them do the job and match the pistons and rings to each cylinder. Or you can just get a complete 1200 upgrade package.