Bent exhaust valve at 130k miles! Why???

My truck is a 1999 Toyota Tacoma 2.7L 4X4 (3RZ-FE) with 135k miles. Problem became clear when I got a cylinder 2 miss fire... So I did a compression test and all cylinders were at 190psi except for cylinder 2 which was at 85psi. So I pulled the head and valves... Upon inspecting the valves I had a bent exhaust valve in that cylinder. I plan on using Plastigage to check the clearance of my camshaft caps, and the timing chain looks to be in great condition. The valve clearances seemed to be off, could that cause a bent valve? I did not see any spots on my pistons where the piston might have contacted the valve. What causes this, and what steps should i take to make sure this does not happen again??

 

Timing chain?

 

Also... The valve stem itself was not bent, just the head of the valve. And only one of the exhaust valves in that cylinder was bent. I dont think the previous owner ever had the valves adjusted. When I brought the engine to TDC and pulled it apart, all timing marks seemed to line up correctly and #1 and #4 piston appear to be fully extended.

 

Im not sure... Should I replace the chain? I have limited skills, all self taught (mostly from reading and youtube/haynes/youtube)
So far I have ordered new exhaust valves, cleaned the head, lapped all valves (except for those I have ordered)...

 

How many miles since it has been done? I suppose more importantly, has the chain ever been replaced? Hope so.
It is most important that this is done.

 

Not sure, I bought the truck 6k miles ago... It has probably never been done!

 

Usually, the 3RZ-FE doesn't ever require a chain change, it isn't like a 5VZ-FE or a 1GR-FE (which are belt driven) the chain only needs changing if it breaks or gets too slack. People generally change the chain on their way to a deeper part as precautionary maintenance, but it isn't required like on a belt driven engine.

Generally if the chain is too slacked that means you'll have more than a one valve issue. I would suggest you have your valves properly clearanced (after buying a new valve) as the exhaust valves have a tendency to tighten up as the motor ages which can cause cracks in the head (and may even be the cause of your bent valve). Possibly have the cam checked as well (probably not necessary)

Also, it may be a good idea to have the timing checked as it is possible it slipped a tooth (if the chain is truly and utterly fucked... very unlikely but easy to check)

Sounds like you are on your way to getting it figured out. Good luck

 

Seems unusual for a 2.7L to have a bent valve at 130k. Check the exhaust manifold to see if there is a big ol crack near vicinity of #2.

Otherwise, since you have the head off, just replace the chain as preventive maintenance.

 

it may be as simple as something fell in the cylinder during a spark plug replacement and that bent the valve before it exited out the exhaust.

is this a sudden problem that arose or you noticed or were you just trying to get it to run better? how long have you had the truck and was it running any different during that time?

in other words do you think its possible you bought it with this existing problem already there?

by the way plastigage is a wax string you mash between bearing journals to check clearances, its not used for valves, for valve clearances you use a regular blade style feeler gage like this: http://www.ebay.com/itm/LASER-2481-...277?pt=LH_DefaultDomain_0&hash=item58b8c3b775

 

or a sticking valve in the guide, weak valve return spring and my favorite? excessive RPM.

Howard