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Discussion Starter #1
So, the new valves and fresh cut seats held good vacuum at the machine shop. They had a witness verify the reading on both heads. But I get them home and decide to test them anyway. Filled the chambers up with water and blew air into the exhaust and intake ports and there wasn't one bubble anywhere. Let them sit overnight, no leaks.
So I bolt them up and decide to run a leak down test before I fill the engine with coolant and oil and whatnot. I put air in both cylinders and get 7.5% leak-down on both cylinders. But the kicker is that there's air coming out of both intakes! There's also some air coming out of the exhausts, but barely.
Now, the percent of leak down is way lower than before, and it's exactly the same on both cylinders, but how is it leaking assembled, but not leaking on the bench with vacuum or water?
And will it quit leaking once the engine is warm and run in a bit?
I hope so or I'm done.
 

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It shouldn't make any difference but..there can be the smallest bit if dust that gets pulled in during assembly that can get between the two surfaces and it will leak until it's gone. I think if you are darn-sure the lash is correct, run it a while and then check. The only other thing that can happen is the heads get a slight warp during torqueing that distorts the seats slightly. Rare...but it has happened. These have been decked..right? I hope that coolant being trapped didn't do something.

On a side note it is a lot easier to force air through something under pressure then to let a liquid sit under static pressure. And vacuum..you can get a max of about 22in but you can put 50+psi with a leak down tester.
 

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We always checked them with solvent.
Last time when he said he got some chatter when he was cutting the seats and then had to lap the valves he should have put solvent in the combustion chambers to see it there was any leakage. They shouldn't have ever left the shop like they did.

Good luck. I hope this is the last time.
 

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Discussion Starter #4
It shouldn't make any difference but..there can be the smallest bit if dust that gets pulled in during assembly that can get between the two surfaces and it will leak until it's gone. I think if you are darn-sure the lash is correct, run it a while and then check. The only other thing that can happen is the heads get a slight warp during torqueing that distorts the seats slightly. Rare...but it has happened. These have been decked..right? I hope that coolant being trapped didn't do something.

On a side note it is a lot easier to force air through something under pressure then to let a liquid sit under static pressure. And vacuum..you can get a max of about 22in but you can put 50+psi with a leak down tester.
Yes, both were decked. And there's no coolant anywhere now. There never was in the rear anyway. And I got a new gasket for the front.

Slight torque of the head would make sense. Bench testing can't replicate that.

I guess I got no choice but to run it and see if heat and motion seal it up. At this point, I wouldn't take it back to the same machine shop, and the only other one around that I know is good is 8 weeks out thanks to Polaris RZR parts constantly coming in the door.
 

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Discussion Starter #5
We always checked them with solvent.
Last time when he said he got some chatter when he was cutting the seats and then had to lap the valves he should have put solvent in the combustion chambers to see it there was any leakage. They shouldn't have ever left the shop like they did.

Good luck. I hope this is the last time.
Yes, they knew they screwed up. They didn't charge me a dime because of it.

I hope this is the last time as well.
 

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Discussion Starter #6 (Edited)
On a side note it is a lot easier to force air through something under pressure then to let a liquid sit under static pressure. And vacuum..you can get a max of about 22in but you can put 50+psi with a leak down tester.
Yeah, all that makes sense too. These pinned the vacuum needle at 22 psi this time, and they said it did the first time too when I just took the rear head in. I'm losing faith in the vacuum method, obviously.
I did the water test more for looking for bubbles with forced air rather than looking for wet leaks, (though I did let it sit overnight with water just to get another verification). That's why I didn't use solvent. I set the compressor at 90 psi and held it inside all the ports and there wasn't one bubble out of all 8 valves.

If I put 20 psi into the leak down tester, the air out the intakes is very slight. If I go up to 50 psi, it tries to throw my breaker bar on the crank bolt into the front fender and the air is twice as loud. If I put 75 psi in there, I have to stand on the breaker bar and the air coming out is enough that it blows my hand off the intake pretty easy. But, even at 75, it's less air coming out then before I had them recut the seats and 40 psi in the cylinder. So there is definitely an improvement.
Also, even at 75 psi, there is barely enough air coming out the tailpipe to feel it. Before, the front cylinder was blowing pretty hard out the tailpipe, so that is another big improvement.
 

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Yes, they knew they screwed up. They didn't charge me a dime because of it.

I hope this is the last time as well.
The problem is they knew it wasn't right when it left their shop.
I hate people like that.
 

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Discussion Starter #8
The problem is they knew it wasn't right when it left their shop.
I hate people like that.
The guy who did the job definitely knew it wasn't right. The shop owner is true blue, so I don't think he was aware. Consequently, when the shop owner found out, I think he fired the guy.
But regardless how it happened, it's not been a very good experience.
 
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Discussion Starter #9
Ok, new theory.....
Since these seats have been cut a few times and the valves sit lower in the head now, is it possible that the springs are relaxed too much and either need to be shimmed or replaced? Just thinking out loud here.
 

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Discussion Starter #11
I got it bolted up and took it for a spin. Seemed to run ok but I could tell a slight hesitation or loss of power. Ran a hot comp test afterwards and the front was 45 psi and the rear was 50. So the rear improved 10 pounds from before this cut, but the front dropped 20 psi. Now, the only thing that was done to the front head since reading 65 was installing 4 new valves and cutting 4 seats. So whatever screwed it up just happened in the last three days while the quad was sitting in my garage, and the heads were at the shop.
That does tend to point to seats are too deep now to keep good spring pressure on the valves.
The machine shop believes that's whats going on. They suggested buying some of the washers that sit under the seats and stacking them 2 or 3 deep under each spring. I asked about just putting new seats in the heads, and they said that was a lot of work and they wouldn't want to do that. From everything I've read, installing new seats is a regular job for any shop.
Hmmm....
 

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Just tossing in that with pressure in the cylinder the spring does nothing to aid in sealing. Heck I used to pressure-up a cylinder so I could remove the keepers & spring to replace seals/wipers and reassemble..all with just air holding the valve shut. Nope, those surfaces should seal by contact alone...they don't flex...that's steel to steel.. so adding spring pressure does nothing. Now alignment changes..as in loose guides or warped stems could change how they sat together during lapping...but they would have to be pretty loose. But lapping you are pushing on the valve head with no spring and then you use the spring to pull the head into the seat afterwards. Just tossing-out thoughts. This is starting to snowball on you. Your compression should be closer to 66-70+. And just an after thought...doesn't that bottom-end now have over 23,000 miles on it? Maybe we don't want all that compression and power..:)
 

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Discussion Starter #13 (Edited)
Just tossing in that with pressure in the cylinder the spring does nothing to aid in sealing. Heck I used to pressure-up a cylinder so I could remove the keepers & spring to replace seals/wipers and reassemble..all with just air holding the valve shut. Nope, those surfaces should seal by contact alone...they don't flex...that's steel to steel.. so adding spring pressure does nothing. Now alignment changes..as in loose guides or warped stems could change how they sat together during lapping...but they would have to be pretty loose. But lapping you are pushing on the valve head with no spring and then you use the spring to pull the head into the seat afterwards. Just tossing-out thoughts. This is starting to snowball on you. Your compression should be closer to 66-70+. And just an after thought...doesn't that bottom-end now have over 23,000 miles on it? Maybe we don't want all that compression and power..:)
Something that backs up your opinion is the fact that when I ran the leak down test after bolting the heads on, that front head was essentially in the same condition it was when it was sitting on my bench 30 minutes before. The springs had not even been touched by the rocker arms because of the valve lash gap at tdc. In other words, the springs hadn't done anything yet, and the valves had not been opened. They hold water on the bench, but loose air pressure when bolted up.
That still points to valve contact not being what it should.

You think I ought to take the heads to a different shop and have them double checked?
 

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Something that backs up your opinion is the fact that when I ran the leak down test after bolting the heads on, that front head was essentially in the same condition it was when it was sitting on my bench 30 minutes before. The springs had not even been touched by the rocker arms because of the valve lash gap at tdc. In other words, the springs hadn't done anything yet, and the valves had not been opened. They hold water on the bench, but loose air pressure when bolted up.
That still points to valve contact not being what it should.

You think I ought to take the heads to a different shop and have them double checked?
I don't know man...most valves leak a little...but yours is apparently leaking enough to bring the compression down to levels that shouldn't be. Unless there is more loss by the rings then we know, your compression is low even with the comp releases to indicate there is a problem. Nova has done way more of these then most of us.. I would be interested in what he thinks. But, yeah either way I wouldn't use that shop again. Enough is enough. You have videos to make GD-it! :)
 

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Discussion Starter #15
I don't know man...most valves leak a little...but yours is apparently leaking enough to bring the compression down to levels that shouldn't be. Unless there is more loss by the rings then we know, your compression is low even with the comp releases to indicate there is a problem. Nova has done way more of these them most of us.. I would be interested in what he thinks. But, yeah either way I wouldn't use that shop again. Enough is enough. You have videos to make GD-it! :)
Yes! I'm dying to ride.

The air coming out the dipstick was very minimal. I couldn't really even hear it over the whoosh coming out of the intake. There's always a little that gets past the rings, so I'd say what was there was actually fantastic.

Yeah, Nova might have dealt with this. He's not been around much lately though.
 

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Discussion Starter #16
So with these wider seats, how about the possibility that the valves will "hammer in" with some run time and heat cycles?
It might be easier to do that right now than tear it apart again. On the other hand, I don't want to burn up the valve edges if it's not going to work.
 

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I use brake cleaner when checking valves.
Keep in mind that even if the valves aren't seated perfectly, once the engine is running the piston motion is so rapid that what actually leaks by should not result in a power loss that you could feel. I've seen engines that had one cylinder down to 20-25lbs due to tight intake valves, but felt fine once they started.
I would try running it if you don't want to take it apart and hand lap the valves yourself.
The material taken off the valve seats won't change the spring tension enough to do anything negative.
Find a better machine shop.
 

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Discussion Starter #18 (Edited)
The last time this shop cut the valve seats on these same heads before the overheat incident, they checked out at 78 front, and 80 rear. I did not leakdown test them then, but the compression test would seem to indicate that the valves were not leaking then.

I kid you guys not, that 3 week period in between my new rear piston/cylinder install and the overheat, this engine was insanely awesome. I was knocking down 22 mpg, and it would wheelie at a rolling 5 mph. At idle, it ran so smooth that my shovel mounted on the rear rack didn't even vibrate. I was having so much fun with it that Murphy just couldn't stand it, and now it's only left the garage twice in 3 and a half months because valves have once again become a problem. It's a crying shame.
 

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So..it was perfect before the overheat. Then after it's never been the same. We know overheating effects many things. I know on these Chinese CFMoto engines it most always means death..either right now or in the very near future...and they don't even have to overheat..just get to 5-bars on the temp meter. Oddly, it's usually that they have rod bearing damage from the super-heated oil, not so much top-end destruction...although the pistons are usually toast.
 

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Discussion Starter #20 (Edited)
So..it was perfect before the overheat. Then after it's never been the same. We know overheating effects many things. I know on these Chinese CFMoto engines it most always means death..either right now or in the very near future...and they don't even have to overheat..just get to 5-bars on the temp meter. Oddly, it's usually that they have rod bearing damage from the super-heated oil, not so much top-end destruction...although the pistons are usually toast.
Yes, but several things point to the overheating not being quite as serious as initially thought.
And even if I'm wrong there, the fact is that the front cylinder held 68 psi, and valve lash was still good after the overheat. It was only when I took the front head off and had 4 new valves and the seats cut last week that it suddenly dropped to 45 psi.
The overheating could not have caused that. Whatever dropped the psi happened last week while the quad was sitting in my garage and the heads were at the shop.
 
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