I bent two valves on my 6g72 it’s a fwd dohc v6, I replaced all 4 valves for that cylinder , it’s cylinder 3 in question. I got 180 psi all around but cylinder 3 was still low but better at 80 psi. I did a leak down test and cylinder 3 failed as expected but all 5 other cylinders got within 5% leak down. I pulled the head back off and did the old compressed air and water trick, found out one of the exhaust valves I didn’t seat properly, i redid the seating process until there were no bubbles doing that test. I threw head back on and now all the cylinders are leaking on that bank. So I changed the headgasket and used copper spray, same thing… inspected the head for cracks, got it resurfaced, same thing. I took the cams off so that there’s no tension on the valves, same thing…. Cylinder 1 is leaking into cylinder 5 and cylinder 3 into cylinder 1, cylinder 5 into cylinder 3. No leaks in the cooling system or crankcase, it’s leaking out the valves some how. Anyone know what could’ve happened? I’m thinking i will need a new block/complete engine.
Who and how was it inspected?? I am assuming a pro machine shop decked the head??
Did you think to have the other head decked the same amount also, could throw off the compression ratio a bit and cause an engine imbalance that you will be chasing later…
Sound like you are trying to lap new valves in the old seats without doing a valve job… Cheeping out has cost you a lot of time, headache and money in the process… I would find a machine shop to properly check the heads, and it sounds like you may have warped your head… And have them do a proper valve job on all 24 valves…
Are you replacing the TTY (torque to yield) head bolts every time you install the cylinder head??
Question, how did you bend 2 valves on one cylinder only?? mechanical failure (broke valve spring etc)? overrevved the engine? jumped timing and got lucky? replacing the timing belt and didn’t have it set correctly??
BTW Gas will find a leak way before water will when checking valves…
When you were lapping (seating?) the valves, what did the new wear pattern look like??
Also consider you have warped the block by removing and replacing the head several times so now it will not seal unless resurfaced.
This engine uses a closed-deck cast iron block. Unlikely to warp, even if severely overheated. Unless deep gouges exist on the mating surface, it is unlikely to need resurfacing.
It is much more probable that all the valves are slightly bent to the point that they don’t seal, but look fine to the untrained eye, or that the heads are warped from overheating or improper removal.
What type of head gaskets are you using (graphite composite, or multi-layer stainless), and are you using new bolts and a proper torque-angle wrench? Are you following the head bolt removal and tightening instructions to a tee?
Thanks for the response, I changed the headbolts 3 times, this is a NA so it’s not like the TT tty bolts. Engine jumped timing and only bent two valves. Machine shop said the valves were just the two were bent, I replaced them myself and just did all 4. He machined the head flat before I replaced the valves. My question is how has the previously unaffected and sealing valves, are now not sealing? Going to assume what you said is true, the head is now warped causing all the valves to not properly seal in the seats. I’m in search of a new head already, but I’ve just never seen this happened and I’ve done valve jobs before on different cars, Honda, bmw, Nissans. First time having this issue so I just want to know why it happened.
That tells me it’s the head gasket leaking, not the valves.
Headgasket leak it would leak into adjacent cylinders, in this case it’s leaking out the ‘closed’ exhaust valves into whatever cylinder has the exhaust valves open. Notice how none of the cylinders leak into adjacent cylinders and vice versa
Here is the basic answer. You did a half ass repair, so you got half ass results. Get the job done right and be done with it.
?? 1 is next to 3, 3 is next to 5.
- Head gasket is not sealing properly, possibly b/c head bolts re-used or not torqued to spec
- Other valves were also damaged when the valve timing skipped, but they just don’t look bent.
Suggest to remove both heads, have all new valves and valve guides installed by a machine shop for all 6 cylinders, and have the same machine shop also check the engine mounting surface and correct any flaws they find there, & replace any studs or threaded holes needing replacing. New head bolts, new head gasket, do that part yourself if you want, done.
That should be caused by a warped head and or warped block, and not the valves (or valve guides as posted above)… You are going to have to buy a straight edge and check the head and block to see what is warped and how bad… Or find machine shop to do what we call in my area a deck and check, they can pressure test the head to find any internal cracks that you can not see as well as check the valves and seats to make sure they are sealing properly…
Not knocking your skill level or experience, but you are defiantly doing something wrong on this one, and making it worse every time you bolt the head back on… But it sounds like it is a head bolt and proper torque sequence issue…
You can also use a large Bastard (flat) file and run it across the head and block deck at different angles looking for high and low spots… If you haven’t done this before, don’t use both hands or push down hard, normally just using the palm of your hand to produce even pressure on the file…again, do not push down hard, the file will easily find any high points… Make sure to remove any metal filings when done…
Unfortunately, we can not see, check out, or anything with this engine, I’m sure there is more to this story…