I get to do a head swap :(

[MK_94_3000GT]

After diagnosing over and over again I think I've found my problem which went away for a while oddly enough. I have no compression over cylinder 6 so I'm thinking valves, all other cylinders are fine so I'm just going to pop the head off confirm my thinking (I hope) and swap a new head on there and reset timing. Car ran for about a week, I didnt drive it though I was on campus most of the time. Anyway one day it just stopped starting. Went back through and checked compression and #6 is ZERO.

This will be fun as I've only pulled a rear head once in the car and it was non turbo and I didnt have to worry about putting it back. So I will have to be more careful to not break shit lol

Wish me luck, I'll take photos and try and document the fun. Oh and Yes I do know its much easier with the engine out. I just left the hoist at my warehouse and dont really wanna pull it even if I had it. I know I can do this, I've done everything else on my cars at this point.

[nogreatloss]

I just finished swapping heads on mine. Really not that difficult. Just remember to buy new head bolts, as the stock ones are usually not able to be re-torqued to spec.

[mh3kgt]

When I had 0 compression on a cylinder, there ended up being a hole in my piston ;)

[B-Man]

You can always get the head checked/decked to be sure it was a valve.

[MK_94_3000GT]

I just finished swapping heads on mine. Really not that difficult. Just remember to buy new head bolts, as the stock ones are usually not able to be re-torqued to spec.

Oh I know its not too difficult, just not something I wanted to do. Got a new head gasket and headbolts already. Thanks though


When I had 0 compression on a cylinder, there ended up being a hole in my piston ;)

I see no reason there would be a hole in my piston, all signs point to problems with my heads/valves


You can always get the head checked/decked to be sure it was a valve.

I will see once I get the head off, if the piston is fine its gotta be my head for one reason or another.

[billbrown72]

good luck.....last night was my last night at work...have 4 days off which will be spent yanking my motor-tranny to begin tear down to see the extent of damage to mine...haven't had the pleasure yet of doing any internal engine work on my car till now!

[CoreyB]

Can you hear where the compression is going ? Have you pulled the valve cover to watch the valves and see how they are acting ? Losing compression completely in one cylinder is odd without hearing something clanging around.

[colt45 gto]

maybe the lifters are blocked and stuck in the fully infated position?
pull the lash adjusters and gently squeeze them out in a vice, if they dont move that thats the problem. but i would pull the open valves and put them in a pilla drill or a drill chuck and rotate them slowly to see if they spin irregularly.

[MK_94_3000GT]

good luck.....last night was my last night at work...have 4 days off which will be spent yanking my motor-tranny to begin tear down to see the extent of damage to mine...haven't had the pleasure yet of doing any internal engine work on my car till now!

Yanking the motor I can do and quickly. I just dislike it completely. Also don't want to dump all my fluids as they are all new :lol: call me cheap. Plus this is a good learning experience for me.


Can you hear where the compression is going ? Have you pulled the valve cover to watch the valves and see how they are acting ? Losing compression completely in one cylinder is odd without hearing something clanging around.

Its going no where. Actually I got the head off one valve is stuck open. Cylinder walls look good, going to further examine potential damage. It didnt run for more than a few seconds this way thankfully.

Anyone know what causes a valve to get stuck open? Also I should note one of my damn lifters is also stuck up. Anyhow I've taken quite a few pictures that I'll put up later. Truthfully its not as bad as everyone says "just pull the motor" Take the hood off and there is plenty of room back there to work. Doesn't make it any more fun but very doable.

[CoreyB]

A lifter being stuck up will cause a valve to be stuck open.

[Chris@Rvengeperformance]

the car should still start, my engine will idle fairly well on 3 cylinders.

[MK_94_3000GT]

the car should still start, my engine will idle fairly well on 3 cylinders.

Interesting note, idk what to tell you it ran before. Not all that well mind you, but it pulled and drove. Then it just stopped starting and I had zero compression on cylinder 6 and upon head removal I've got a stuck valve. I am not sure if that means I have other problems or what based on what you're saying but we'll see.

[Chris@Rvengeperformance]

i see the thread got straightened out and read the other posts. The valve guides are probably bad or the valve is bent.

[MK_94_3000GT]

The car should still start like that though?

[Chris@Rvengeperformance]

I'm not sure, but I'd think so. Mine runs with all 3 rear injectors unplugged. Unless the valve is so bound that the engine just stalls.

[MK_94_3000GT]

Injectors unplugged is different than a valve being stuck open. My valve was open. Cutting fuel to 3 is fine but nothing can escape in that situation. I am thinking thats what caused it to stop running as I have no reason to believe it was anything else. Car ran fine before.

[BaadVR4]

Now that the head is off, I'm sure you noticed you have drained most of the coolant, just like you would pulling the motor. And the probability of coolant contaminating the oil is high, so the oil will need to be changed. What other fluids are there? Trans fluid? That generally doesn't leak when pulling the engine. But I applaud your choice to pull the head with the engine in the car. As to the valve stuck open, that is generally caused by a bent valve. Stuck lifters are a different story. Either the lifter is "pumped up" (lifter stuck in the "open" position) because the lifter won't drain or there is clearance between the lifter/lifter bore and the lifter is cocked in the open position. Changing the head will probably fix the symptoms here. But if the issue is a bent valve, then changing the head may not solve the problem. If the valve is bent, something caused it.
The most common cause of a bent valve is the valve hitting the piston. If the lifter is "pumped up", it needs to be replaced. What about the rest of the lifters? IPS is having a sale on big bore lifters, so maybe a total replacement is in order.
If I were doing the job, I'd make certain both the problem and the cause of the problem were fully explored and resolved before I fired the engine again. Just my 1.5 cents worth.

[MK_94_3000GT]

Now that the head is off, I'm sure you noticed you have drained most of the coolant, just like you would pulling the motor. And the probability of coolant contaminating the oil is high, so the oil will need to be changed. What other fluids are there? Trans fluid? That generally doesn't leak when pulling the engine. But I applaud your choice to pull the head with the engine in the car. As to the valve stuck open, that is generally caused by a bent valve. Stuck lifters are a different story. Either the lifter is "pumped up" (lifter stuck in the "open" position) because the lifter won't drain or there is clearance between the lifter/lifter bore and the lifter is cocked in the open position. Changing the head will probably fix the symptoms here. But if the issue is a bent valve, then changing the head may not solve the problem. If the valve is bent, something caused it.
The most common cause of a bent valve is the valve hitting the piston. If the lifter is "pumped up", it needs to be replaced. What about the rest of the lifters? IPS is having a sale on big bore lifters, so maybe a total replacement is in order.
If I were doing the job, I'd make certain both the problem and the cause of the problem were fully explored and resolved before I fired the engine again. Just my 1.5 cents worth.

I drained both the coolant and the oil before starting this, so not much coolant spilled. Furthermore I plan to flush the car with oil several times to make sure there is no problems.

As for why the valve is stuck/bent or what have you. My guess is the previous owner of the car that this motor came from set timing wrong. Thus by my correctly setting it I would be in hopes that I have cured the problem at hand. I cant say much more than that as everything else on the motor seems ok.

[BaadVR4]

I drained both the coolant and the oil before starting this, so not much coolant spilled. Furthermore I plan to flush the car with oil several times to make sure there is no problems.

As for why the valve is stuck/bent or what have you. My guess is the previous owner of the car that this motor came from set timing wrong. Thus by my correctly setting it I would be in hopes that I have cured the problem at hand. I cant say much more than that as everything else on the motor seems ok.

If by "set the timing wrong" you mean mistiming the camshafts/crankshaft, I would agree that could cause a valve to hit a piston and bend the valve, causing it to hang open and result in zero compression in that cylinder. And the hanging valve could cause the lifter to stay all the way open because there is no pressure from the valve spring to close it. In general, camshaft/crankshaft timing far enough out to bend one valve will bend others, although only bending one is certainly a reasonable scenario.
Whatever the case, I would replace at least the one lifter that is open, if not all in the rear bank. Just my 1.5 cents worth.

[MK_94_3000GT]

If by "set the timing wrong" you mean mistiming the camshafts/crankshaft, I would agree that could cause a valve to hit a piston and bend the valve, causing it to hang open and result in zero compression in that cylinder. And the hanging valve could cause the lifter to stay all the way open because there is no pressure from the valve spring to close it. In general, camshaft/crankshaft timing far enough out to bend one valve will bend others, although only bending one is certainly a reasonable scenario.
Whatever the case, I would replace at least the one lifter that is open, if not all in the rear bank. Just my 1.5 cents worth.

Yea I thought it was weird that not all the valves bent, however odd as it may be the timing of the cams was set just not along with the crank. The motor was not in TDC when set. I can say after I fixed that problem the car ran just not well. After getting a zero compression reading over cylinder 6 I have since removed the head and discovered my stuck/bent valve. The piston looks fine, cylinder wall looks good. I've no reason to believe anything else is wrong other than that valve somehow got bent due to being mistimed and thus is my problem. I will flush and drain the system again and go back over the bearings just to be safe however oil pressure was good when it ran. I think I'm nearing the end of this problem so hopefully I'll have my DD back soon.

[BaadVR4]

Yea I thought it was weird that not all the valves bent, however odd as it may be the timing of the cams was set just not along with the crank. The motor was not in TDC when set. I can say after I fixed that problem the car ran just not well. After getting a zero compression reading over cylinder 6 I have since removed the head and discovered my stuck/bent valve. The piston looks fine, cylinder wall looks good. I've no reason to believe anything else is wrong other than that valve somehow got bent due to being mistimed and thus is my problem. I will flush and drain the system again and go back over the bearings just to be safe however oil pressure was good when it ran. I think I'm nearing the end of this problem so hopefully I'll have my DD back soon.

Sounds like you're headed in the right direction. Please consider replacing that lifter, it is also possible that the bent valve was caused by the lifter "pumping up" and holding the valve open so that it was tapped by the piston, bending it. Replacing the lifter is cheap insurance against this happening again. Just my 1.5 cents.

[MK_94_3000GT]

Sounds like you're headed in the right direction. Please consider replacing that lifter, it is also possible that the bent valve was caused by the lifter "pumping up" and holding the valve open so that it was tapped by the piston, bending it. Replacing the lifter is cheap insurance against this happening again. Just my 1.5 cents.

I actually replaced the entire head and I'm fully rebuilding the old one. I just don't have time to rebuild it at the moment so I took it from my other car that is a few months away from being finished.

[Mike-92RT]

a valve stuck open could be a lifter stuck up, like coreyb said... there could also be gunk stuck on the valve, the valve could be bent some how, and jammed in the valve guide. Something could also be wrong with the rocker arm.

[CoreyB]

How open are we talking ? Any sign of the piston hitting the valve?

[MK_94_3000GT]

a valve stuck open could be a lifter stuck up, like coreyb said... there could also be gunk stuck on the valve, the valve could be bent some how, and jammed in the valve guide. Something could also be wrong with the rocker arm.

Regardless of what it is that is wrong I am replacing the entire head with a known working head that is ready to go. I will be rebuilding the head for later use.


How open are we talking ? Any sign of the piston hitting the valve?

No sign of piston hitting the valve. Cylinder walls are good, it was not stuck very far open. Car didn't run more than a few seconds in this condition

[MK_94_3000GT]

New head in, just a matter of resetting timing and putting everything back in where it goes. A ton of misc shit that is just annoying :lol: Anyway should be up and running soon.

[mh3kgt]

Good to hear. I may be doing a front head swap in the near future as well. Stupid VSS :mad:

[MK_94_3000GT]

After delaying for way too long I got it running!!! Bent/stuck valve was the cause of all my headaches. New head in and my car runs great, DR650s are fun!!!! Got my DD back.