Bent Valve Phenomenon

propeine · Aug 7, 2008

So my car decided that it wanted to sound like a subaru after my timing belt replacement/BC 272 install. DSMLink was showing wacky numbers and the car sounded more than just "cammed". Decided I'd run a compression test. 180, 178, 178, 28. Well what the hell is up with that? So I do a leakdown test on the suspect cylinder and everything is coming out the exhaust. Must be valves right?

Pulled the head today and sure enough both exhaust valves are bent but...the kicker is all the timing marks lined up before and trust me I checked 100 times and rotated the motor over by hand probably 30 revolutions total. The other thing I don't understand is there isnt a single mark on the piston or valves that indicate they came in contact with one another. Finally its only that one cylinder. Anyone else ever have something like that happen?

VETTE_50_TH · Aug 7, 2008

Im sure you did becuase if you didnt, you would have a slew of bent valves. More than likely all of them. Thats very weird to here only two valves are bent.

James :laser:

crensinivon · Aug 7, 2008

How's the spring rate on those exhaust valves? But at least you only bent two.

VETTE_50_TH · Aug 7, 2008

crensinivon said:
How's the spring rate on those exhaust valves? But at least you only bent two.

Either way it has to be machined. The guides have to be replaced more than likely and those valves. Might as well get the whole head redone.

James :laser:

crensinivon · Aug 7, 2008

Yeah I just didn't want him to do it again.

Something caused it to fail now you just have to figure out what.

silver bullit · Aug 7, 2008

Or you did not bleed the lifters.

propeine · Aug 7, 2008

silver bullit said:
Or you did not bleed the lifters.

Brand new lifters at the same time.

and yes crensinivon thats my problem I don't know how it happened so I'm concerned about it happening again. The head/block had never been seperated before and I don't think the revs were ever high enough to get float and bend them that way. Sooo confused.

silver bullit · Aug 7, 2008

propeine said:
Brand new lifters at the same time.

and yes crensinivon thats my problem I don't know how it happened so I'm concerned about it happening again. The head/block had never been seperated before and I don't think the revs were ever high enough to get float and bend them that way. Sooo confused.

Yep you did not bleed them or did it correctly.

Hence the bent valves.

crensinivon · Aug 7, 2008

Did you replace the springs. Its still possible to get float on springs at a low rev with bad springs which is why I asked about spring tension. Maybe the rockers were a bit off when you installed the cams and not set properly on the lifters. I don't think bleeding was the problem, especially with new lifters and it only happening on two valves side by side.

propeine · Aug 7, 2008

I didn't replace the springs at that time even though I had them due to mostly being too lazy to make a valve spring compressor and too cheap to buy one. Serves me right I suppose. I've got new retainers and springs for this time around though.

I wasn't aware new lifters needed bled. The rockers not seated properly seems possible although it is strange to have it happen to the two exhaust valves in the cylinder.

The valve float issue seems possible too. If those springs were tired under the stock cams then 272's could have cause them to float at low rpm. That would explain the lack of marks on the piston or valves and not binding while turning the motor over by hand.

crensinivon · Aug 7, 2008

Most chain auto parts stores will rent you a valve spring compressor buy it and take it back. I know autozone my way does. No need to build one.

If the springs were weak, the rockers could have jumped causing the valve to bend.

Were the valves bent by the cam or by the piston?

Freerevving · Aug 7, 2008

valve float is not going to happen at low rpm, and stock mitsubishi springs are sufficient at high rpm
weak springs will not cause your valves to bend (well I suppose it's possible on a drag car, but highly unlikely)

You should be a little worried if you're revving to 8500... but your bent valve problem is going to have something to do with timing

Your "sounds more than cammed" description is typical of being one or two teeth off

I bought a 4g63 with the timing two teeth off on the exhaust... it ended up having two bent exhaust valves

propeine · Aug 7, 2008

Freerevving said:
valve float is not going to happen at low rpm, and stock mitsubishi springs are sufficient at high rpm
weak springs will not cause your valves to bend (well I suppose it's possible on a drag car, but highly unlikely)

You should be a little worried if you're revving to 8500... but your bent valve problem is going to have something to do with timing

Your "sounds more than cammed" description is typical of being one or two teeth off

I bought a 4g63 with the timing two teeth off on the exhaust... it ended up having two bent exhaust valves

The "sounds more than cammed" was after my motor decided it was only going to use three cylinders. If my timing was off I hope I would have noticed it when spinning by a 1/2 in drive ratchet on the crank and more than likely would have bent more than just those two valves. Also I would imagine there would be some indication of contact with the piston.

As for the valvespring compressor I had read that no one has found one at a chain store that is usable on our head due to the tight space in there. Toyotool and a few others make them that work with the head on but most the traditional kind don't work. I'll go take a look at the local advance auto and see tomorrow. The bend was near the valve seat so I assume the piston did the bending but like I said I cant see any physical indication they ever made contact.

crensinivon · Aug 7, 2008

Well I wonder if when you were spinning it by hand if you didn't mistake valve for compression and bend them lightly?

Freerevving · Aug 7, 2008

propeine said:
The "sounds more than cammed" was after my motor decided it was only going to use three cylinders. If my timing was off I hope I would have noticed it when spinning by a 1/2 in drive ratchet on the crank and more than likely would have bent more than just those two valves. Also I would imagine there would be some indication of contact with the piston.

As for the valvespring compressor I had read that no one has found one at a chain store that is usable on our head due to the tight space in there. Toyotool and a few others make them that work with the head on but most the traditional kind don't work. I'll go take a look at the local advance auto and see tomorrow. The bend was near the valve seat so I assume the piston did the bending but like I said I cant see any physical indication they ever made contact.

Hmm.. I agree it's a phenomenon

To the other poster... the valve is not going to bend against anything but the piston... what's causing the valve to hit the piston is still in question

IMO there is now only two likely causes for this:
A lifter that was filled...
The valves seized because of high mileage warpage or crud above the valve guide... and the extra lift jammed them up...
more likely the first one

Either way the fix is still the same... just remember to have the valve guides checked... but you probably won't need to replace them unless they're bronze

VETTE_50_TH · Aug 7, 2008

Heres the thing. If the lifters weren't bled and still have oil in them and aren't compressing all the way, do you really think it would hold any pressure?? I dunno. Take those lifters out and bleed them. Put them back in and see what happens.

James :laser:

propeine · Aug 8, 2008

I'll bet money I figured it out. When I was reefing on the cam gear bolts to get them out...everyone knows how tight those things are, I bet part of the force holding it in place was on those two valves. In other words I'll bet it rotated enough that the valves were pushing on the piston when I was using a three foot breaker bar on the 17mm bolt. If you look at the position of the dowel pin at 12 oclock it wouldn't take much rotation if the timing belt wasn't on. I thought it was left on when I was doing that but this seems to be the most plausible explanation.

Freerevving · Aug 8, 2008

propeine said:
I'll bet money I figured it out. When I was reefing on the cam gear bolts to get them out...everyone knows how tight those things are, I bet part of the force holding it in place was on those two valves. In other words I'll bet it rotated enough that the valves were pushing on the piston when I was using a three foot breaker bar on the 17mm bolt. If you look at the position of the dowel pin at 12 oclock it wouldn't take much rotation if the timing belt wasn't on. I thought it was left on when I was doing that but this seems to be the most plausible explanation.

you seem to have left that part out

well the guessing game was fun while it lasted

propeine · Aug 8, 2008

Freerevving said:
you seem to have left that part out

well the guessing game was fun while it lasted

Didnt even realize it til someone else mentioned that I may have had the valves hit together when I was aligning the cams. Still just a hunch but it makes perfect sence

VETTE_50_TH · Aug 8, 2008

I dont know about that one. That motor should have been at TDC when you put that on. And you would have def. hear them clatter against each other. And there would have been some force against it. Take the head off and see what you find.

James :laser:

propeine · Aug 8, 2008

VETTE_50_TH said:
I dont know about that one. That motor should have been at TDC when you put that on. And you would have def. hear them clatter against each other. And there would have been some force against it. Take the head off and see what you find.

James

Head has been off since I started the post. I can take some pictures if anyone really wants to see.

Freerevving · Aug 8, 2008

I think you've found it because I believe the #4 cylinder exhaust valves (or is it #1?) is most likely to hit at TDC

It would take a 3 foot bar to bend them OMG

VETTE_50_TH · Aug 8, 2008

That would help.

James :laser:

VETTE_50_TH · Aug 8, 2008

Freerevving said:
I think you've found it because I believe the #4 cylinder exhaust valves (or is it #1?) is most likely to hit at TDC

Here is the thing, the number 1 and 4 cylinders move with each other. If he were to bend those two valves, that means that the two valves down at the other side would have had the same thing happen. Unless of course he has one of those boomerang cams that i hear are all the rage.

James

Freerevving · Aug 8, 2008

well at TDC, if you crank counter-clockwise on the cams, the camshaft will open the #4 cylinder exhaust valves (could be #1, can't remember firing order).. If the belt is off they'll hit the piston... I'm pretty sure it's #4 cylinder

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Bent Valve Phenomenon

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