TOPIC:

I recently just finished rebuilding my engine and got to that point when it was time to let her start, and essentially got nothing. Before I give up I figured I would get some opinions here. I put brand new stock rings on there and did a valve job on my own. I checked the clearances on both the valves and the tolerance on the piston walls and all were found to be good. Here is a little bit of the wierd part. I did some research on how to place the pistons back in the bores and decdied to put them in dry. After I figured out it still had low compression I decided to try putting some WD40 in through the spark plug holes. Low and behold my compression came up to spec on my left two bores, and even up 20 on my right two. My left were above 100 psi, but the right weren't quite there. Now if I hadn't rebuilt, I would think this would suggest bad rings, but I know they are good. Do I need to keep wetting down those bores and see if the compression stays? Did they just not seat correctly? I would appreciate and opinion for some of you out there. Plus what would everyone suggest to put down those bores instead of wd40 that might help me a bit more?

Did you hone the cylinders to break the glaze?

yes, and with a crosshatched pattern.

If you used a fairly coarse stone you might need to run dray for a few minutes.

If you used beveled rings, did you put them in 'right side up'?

Did you check the end gaps and did you stagger per the manual?
It's not unheard of for someone to ship the wrong size rings, esp if you bought on ebay.

You might try putting some compressed air in on the top of the compression stroke and listen for leak around the valves.

-Duck

Post edited by: Duck, at: 2006/10/15 17:32

Thanks for the reply. You might have a point on the course stones. I did check for the beveled end, mainly because I asked about that on this site before I set things in. So I am almost positive everything is as it should be on that end. I can try that with compressed air and just see if I can figure it out. I thought it was just wierd that I put some wd40 in there and that almost instantly raised the compression so much.

If addition of WD40 or oil raises compression this indicates that the rings are not seating. As suggested, do a leak down test. This will determine where you are losing compression, IE: rings, valves----

Has the engine been run at all since the rebuild? maybe the rings just arent broken in yet and compression will get better after its been run a bit...

So is there an easy way to get them to reseat without tearing the whole thing down? I did get it to run barely, but maybe for a minute or two. Think it needs a better break in?

are you using synthetic oil? I was told rings wont break in very good at all with synthetic.

Breaking in rings requires more than a few moments running, unless you are using moly coated rings and do a couple or three wide open blasts.

So no, the rings are not seated yet.

The compression does seem rather low for a freshly assembled motor though, you sure you staggered the ring gaps and that all the clearances are correct?
Same with the cam timing and valve clearances?

I know everything was staggard and I rechecked the which end was up on every ring. According to what I found, the facotory rings I got only had a stamp or a bevel on the second ring from the top. I had asked some people on this site about this, and I was told it wasn;t unusual for that to happen. I was told that the others probably wouldn't matter in that case if they had no bevel or stamp to show correct orientation. What would you suggest the best way to break these rings in? The thing will barely start, and it is a bear to keep going.

First you need to find the reason for the really low compression and fix it.

Did you rebuild the head, as in lap the valves, check/replace the valve guides, adjust the valve clearances, time the cams?

Ok, I went back and read your original post again, and it seems you have done the above.

But the point remains that the compression is entirely to low for a rebuilt motor.

I know it's not what you want to do, but you need to pull the head and cylinders and find out what's wrong. It's the right thing to do.

Recheck "Everything", it's the attention to detail that makes the difference between a good running motor and one that will barely get out of it's own way.

Post edited by: steell, at: 2006/10/16 07:57