Determining bent valves

[Majordisorder]

My 98 Frontier with 2.4L 4-cyl. died recently. Upon taking it apart, it was obvious the lower timing chain guide and tensioner were destroyed, with lots of pieces deposited in the oil pan. The chain never actually broke so plan A is to fit the cheapest aftermarket timing chains, sprockets, and tensioners I could find, and first see if the motor will rotate correctly with timing re set. If it does, I'm thinking basic compression test. My concern is rotating the engine by starter motor with no oil pump installed. Since it is timing chains, the upper and lower covers would need to be re-sealed and installed to install the oil pump (as well as pan, then fill with oil)

I would like to avoid doing all this if it turns out the head needs removed due to bad valves. Am I over thinking this? I could squirt oil on the lifters and down spark plug holes, but the only oil on the crank and connecting rods would be whatever is left.

Any suggestions?

 

[APEowner]

If you bent a valve there will be zero compression on the affected cylinder. You should be able to tell that just by turning the engine over by hand.

 

[cvairwerks]

Roll the engine with the crank pulley bolt and no plugs. IF everything lines up prior to pulling the chain, you may have gotten away with no valve to piston contact. IF it doesn't line up correctly, pull the head and go from there.

Depends on where the valve bends at whether you loose compression or not. Bend the upper inch or so of the stem and the valve may still seal.

 

[scissorman]

Your engine IS an interference engine meaning that when the crank and cam are not in sync it will bend valves.

 

[Rlfd213]

The only real way of knowing is to take the head off and send it out. You can’t do a compression or leakdown test unless you repair the chain and put it all back together and in synch.

 

[BADSIX]

To answer your question about can I run the starter motor with out the oil pump, yes for short periods like checking compression will be ok. if the old chain is still on the sprockets check to see if all the timing marks line up as they are suppose to. it most likely skipped a few teeth when the tensioner gave up.
Jay D.

 

[Ole Slewfoot]

If you bent a valve there will be zero compression on the affected cylinder. You should be able to tell that just by turning the engine over by hand.

Not so, sometimes they only bend a little bit. pour light oil in the port and see if it comes out the valve is what I usually do.
a leakdown test on car will get you in the ballpark.

If you have hydaraulic lifers, they don't work right without oil.

 

[LXCam]

There no reason to spend a dime yet or go thru all that^^. Take all the plugs out and rotate each cylinder to almost TDC of the compression stroke and blow air into the cylinder. You'll need to hold the crank in place or it'll spin the damn thing and you'll need to make certain the air nozzle fits tight to the spark plug hole. I would also suggest you turn down the pressure to 20-50psi. If you have a bent valve you'll hear air coming out of either the intake or the exhaust. Btw, a leakdown tester will make this chore easier if you can get your hands on one.

 

[Majordisorder]

Thanks for all the suggestions. When the chains and tensioners arrive, I will get it mechanically timed again, and check with air when each cylinder is at TDC. (Thanks LXCam). Simple enough to do and will determine if I go with plan B (more than likely) and tear it down and get valve job. Plan C will be if any piston damage.

Thought I would add: I bought a Toyota Tacoma 4wd today(used with 153K)

 

[BillK]

md,
My engine builders software says that it is an interference engine, meaning it does bend valves.

 

[T_R]

On a 1998 truck, a used engine is going to be cheaper than a repair. I bet with some searching you can find one for a couple hundred bucks.

I wouldn't even mess with it.

 

[no704]

Beg borrow or steel a bore scope and look for piston damage thru the plug holes.

 

[jdsac]

Whatever you do, don't use the starter. Turn by hand only.

 

[BillK]

On a 1998 truck, a used engine is going to be cheaper than a repair..

But chances of finding a decent 20 year old engine are pretty slim.

 

[ratdoggy]

Can you pull the rocker covers off and to turn the engine by hand see if the valves are closed. Then pump some air in there with a leakdown tester?
Didn't see post #8

 

[T_R]

But chances of finding a decent 20 year old engine are pretty slim.

They are good in my experience. Especially on a Japanese engine from the 90's. They were all pretty good by then. Buy something from a low mileage wreck say less than 150k. You know it was running when the car was wrecked.

 

[EOC_Jason]

Subscribed just to see what the outcome is!

 

[Majordisorder]

The cheapest timing chain kit arrived today so now have some new tensioners and guides to lock in the timing, rotate the engine and do some testing. I'm expecting the worse and if compression isn't right, will for sure pull the head off and send it out.

Before putting it back together, I will for sure purchase a kit with oil pump, water pump, and higher quality components than what I received. The new chains are far more loose that the originals, the chain guide has a broken tab and hasn't been out its plastic bag yet. It's cheap looking but impressive they could sell all that junk for 18.95 and free freight. Four sprockets, two chains, two chain tensioners, two chain guides, misc. small parts, maybe they will end up in some art project.

 

[Majordisorder]

Not owning any leak down tester, I gutted a spark plug by chucking it in the lathe and cut in just below the porcelain, ground off the spark arm, and welded in a piece of 16mm ss tube, as well as a modified male quick connector. Worked real well. Told me that there is no compression in any cylinders when they are at tdc with both valves in closed position.

So on to plan B and remove the head with the thought of sending it out for a valve job. And will be looking into used engines as well.

 

[EOC_Jason]

Damn that *****... But at least we will have some interesting pictures when you take it apart.

 

[Ole Slewfoot]

Once everything is clean, measure piston height in 2 directions on each hole, a bent rod will sit low.

 

[Majordisorder]

All of the intake valves hit pistons. Shown are the two middle cylinders and corresponding valves.

The intake valves were all stuck just short of seating, the exhaust valves were all ok.

I'm considering just polishing the dented pistons and replace the intake valves. Might get another 50,000 out of it.

 

[larry4406]

Years ago I had a motorcycle that sucked a valve and hit the piston like you showed. I replaced the head but blended and smoothed the piston impact damage. Did the smoothing/blending with a file and crocus cloth with the piston in the bore. Cleaned it well. Worked for me, not saying you will have same success.

 

[BADSIX]

I wouldn't touch the pistons, those little dings aren't going to hurt anything.
Jay D.

 

[Majordisorder]

On a 1998 truck, a used engine is going to be cheaper than a repair. I bet with some searching you can find one for a couple hundred bucks.

I wouldn't even mess with it.

I would have to agree that this was the best advice. I was most of the day tearing down this motor, some broken bolts, aged hoses that suffered the process, etc.

Ordered 8 intake valves with the intent of bringing the head back into spec. If upon inspection it requires more than just fitting new intake valves, it will get sent out. If the right motor appears, I still might go that route. Thanks again for all the advice.

 

[Paperman]

View media item 77956

 

[Majordisorder]

Good one Paperman

I completely disassembled the head and was lucky only the intake valves were bent. The new ones as well as the exhaust are all lapped and back in. Everything else checked out as well: springs, guides, warpage, etc.

My plan is to mic all the bucket shims so when it is back together and clearance is checked I will know what shims are needed. Not sure about this step and would appreciate any info if anyone knows.