Stuck valve? Rings? Both?

So got my 'parts bike' started - poor thing had been left out in the rain for who knows how long, and it ttok a good bit of trying to remove moisture before I could even get a spark to fire. Finally fires up, and blows TONs of crap out the exhaust. Muddy, rusty looking water. Change the oil (which was milky) and start her up again, and let it run for a bit.

Eventually it smoothed out, and the smoking became less and less of an issue. Bike has aftermarket exhaust - 2 into 1 setup. Cylinders 3-4 clear up the fastest, and eventually stop smoking. But cylinders 1-2 took much longer to clear up (exhaust is still 'wet') and backfires pretty consistently.

Now its really not smoking much at all, plugs look decent, but the backfiring is still there on #1. Did a compression check, and got 125-130 on 2, 3, and 4 - but 1 comes out at 70. OLD (like 40+ yrs) push-type gauge, so I wouldn't be surprised if it's off a little, but that doesn't change cylinder 1. Anyway, put a cap full of oil in 1, and bumps up to about 80-85.

Given that this thing sat with water in it for maybe 2 years, but turned over very easy, what might I be looking at? Rings? Stuck valve maybe with all the crap that was under the plugs?

I was going to use this engine in place of the one I have already - even with the backfiring - it seemed really smooth and pretty quiet, and has 17k on it versus about 50k on mine. Now I'm guessing that wont happen this summer...

 

Just doing the same with my 900, no comp on #2 got it stripped down & no real evidence, probable part rings gummed up & part valves not seating great, pity you have to strip it to find out.

 

Anything I should try before I break it down? What should I look for first? Looks like the other engine will be going in after all, lol.

 

Hold that pot on T.D.C. with a wrench on the left crank end, put shop air into the plug hole & see if air is coming out the exhaust or inlet vatve.

 

If you're only coming up 10-15psi on the wet test your problem isn't rings. It'll be valves, head gasket, something like that.

 

I'm starting to think valve myself, will try the air trick to check the exhaust port tonight. With all the crud that was in there, valve not seating right would make since.

As far as compression, wanted to see what you guys think. I'm not sold that this gauge isn't off either. The other cylinders checked out at 125, all three. Motor has 17,000.

Checked my 50k + motor with a different gauge, got 150, 145, 150, 140.

What are typically healthy numbers like on these bikes?

 

The Clymer guide for my 550 says 130-160 is normal. Looks like you're golden on the second engine, a little low on the first.

 

Keep one thing in mind; the actual reading may vary from gauge to gauge, it's the comparative readings that matter.

It does pay to use a second gauge; kind of like getting a second opinion.

 

Question - I haven't had a chance to check to see if its a stuck/not seating valve yet (though I'm pretty sure it is)... but I did realize this morning while thinking about it that I completely forgot to hold the throttle open while testing the compression. Anyone know offhand - with it getting 125 on 2, 3, and 4 - how would actually holding the throttle open possibly affect those numbers?

 

Yes.
Definitely so.
With the Throttles CLOSED ... the Maxixum Volume of Intake Air to Compress will be less, ... causing the reading to be inaccurate.

Tie or Tape the Throttles Wide Open.
The Battery should be Fully Charged; too.

 

any idea how much it might affect them off the top of your head? think it'd be enough to put here in the 'golden' 130-160 range?

 

Opening the throttle will give another 10-20 PSI. Don't ask how I know this.

 

ha, thanks.

 

ALSO remove the air filter & ground the plugs on the head.

 

Thanks - got 150 on 3 and 4... but stayed at 125 on 2, and a measly 75 on 1. Looks like this one is becoming the project motor!

 

if its been sitting for a long time you could have rust on a valve seat. The head will need to come off and the valves checked for that cylinder.


MN

 

Buck-fifty on three and four. Very good to Excellent.

Oh, only a buck and a quarter on two. Borderline.
On, no. Seventy on one. Owooo. Not good.

You want to take your time removing the Head. Don't do anything to harm the Gasket while you are taking the Head off.
That Gasket might have a "Tell-tale Sign" indicating that there's a problem with the Gasket or how the Head was torqued.

You have to look for "Footprints and Fingerprints" of the Gasket possibly being at fault, here.
You might be looking at something as simple as taking the Head off and having the Head's Mating Surface "plained" ... where they set-up the Machine and take-off as little as a few thousandths to take a slight WARP out of the Head.

Good Luck.

 

Thanks for the tips guys. I'm thinking its the valve seating. The plugs were filthy underneath on that side when I removed them, like they'd not even been in place; water and mud? and rust. Pulled the intake boots and it was obvious that those two weren't firing right - wet and gunked up on the intake side. I'll put the other motor in for now - 50k + and doesn't feel as smooth shifting, but its got good compression. This will be my first ventured past the valve cover - but I'll take my time and hopefully find its a relatively inexpensive fix. If so, I've have something with lower miles I can get going and take my time with making it look good too!