The Top DSM Community on the Web

For 1990-1999 Mitsubishi Eclipse, Eagle Talon, Plymouth Laser, and Galant VR-4 Owners. Log in to remove most ads.

Please Support Morrison Fabrications
Please Support ExtremePSI

Bent valves a third time? Motor just broken?

This site may earn a commission from merchant
affiliate links, including eBay, Amazon, and others.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

deflator

15+ Year Contributor
535
3
Jan 5, 2007
livonia, Michigan
I keep rebuilding this head and it just keeps bending the valves on start up. I think I am doing everything right, tensioning the belt with the Jay's racing tool. Timing looks good but all I get is backfire and no-start.

I had some serious head carnage that put the car down a year ago, all the valves hit the pistons and a rocker arm was cracked in half. Pistons are gouged but seemed serviceable. Turns out I forgot the woodruf key for the crank and I thought that was why I jumped timing. So I rebuilt the head, put a key in, and it is no different.

The engine does not turn over smoothly when cranking, it sticks in places and the interior lights dim and it stops cranking. Same crap as before when I tried to start it and it jumped timing because there was no woodruf key on the crank.

After 7 years of BS I'm thinking it is part-out time. But the car is just so mint I can't stand giving up without exhausting the possibilities. Please advise
 
You either have the lifters pumped up, too tall of valve height, or you are continuing to set the timing wrong. It is possible that you either have the plate on the crank with the timing mark backwards, or the wrong one.
 
Lifters are brand new topline ones this time and I bled them and made sure they compressed easily by hand.

The bottom end turns freely by hand, everything turns easily until you put plugs in. There are places it is harder to turn than others, and the engine seems to want to turn backwards at some points. Odd, but I attributed it to the Dual valve springs' pressure.

I made new timing marks on the plate this time after putting it at TDC. Everything on the crank was right this time, including torque on the crank bolt. I have no marks on the harmonic dampner since it is a 6bolt swap, so I am not 100% timing is still perfect until I take off the lower timing belt cover. All I can tell now is the cams still match up and the piston appears to be at TDC at that point.

I timed this engine once just fine, using this timing plate. The cams were just too aggressive and that caused it to let go.

It must be either a new, but faulty tensioner, these damaged cams, the rebuilt head, or I am just doing something wrong setting timing.
 
Timing! Unless you had crank work done, put in new valves that are too long, too big of a cam shaft, or block/head resurfacing, it's a timing issue when all valves make contact. Something is WAY off if you are bending valves still, if you rotated by hand you would have felt the metal to metal contact, before blowing another set of valves.

Rotate with all plugs out, should be easy pie and you should feel just the lopes of the crank.
Put the plugs in, do the same thing, should be the same feeling but much harder to turn the crank.

if you do 6 FULL rotation's of the crank each way, and nothing is hitting, you should be in the right direction.

1 Tooth off, no damage, 2-3 off your playing with fire, more then 3 Russian roulette.


Why make new timing marks?


Bottom end turns freely? Is the head not attached when you are doing this?

Also where are the valves bending, any contact on the valve head from the piston?
 
How thick is the head? How many times has it been decked? You may just have a really thin head and the machinist(like most) knew nothing of 4g63s and said "hey, it looks good". You are one determined son of a bi***, ill give ya that. I thought i knew frustration! Can't believe you're still with it after bending valves like that and putting in countless hours, plus the money. Hope the 4th time is a charm!
 
Head was resurfaced twice and my machinist knows these cars. Putting it back together so many times may be the problem, I know how to put it back together but maybe I am messing up somewhere.

The timing mark on the plate wore off. It is a trimmed-up 2g one on a 6 bolt.

Bottom end turned nicely without the head. I checked it out after the valve impacts and it seems to only have suffered cosmetically on the piston tops. I turned the engine many times by hand checking the time and it seemed ok.

Now it requires more effort at points to turn, and will turn backward at points. Maybe it is the cams. The original blowup was so violent it shattered a cam gear. If the car needs new cams and a little valve work again, wth after all this other work.

Someone on the link forum suggested the cam dowels broke and the gears are spinning on the cams, but I haven't had time to verify that.
 
The 2g timing plate is totally different with a different timing mark location. You need to get the right parts and stop guessing. What cams are you running. I see no way for the cams to be defective to cause this. You need to get the correct timing plate, verify that the key on the crank pulley isn't sheered and than install the new correct 6 bolt timing plate. Next you need to torque the crank bolt properly so there is no chance of sheering the key. Next you need to pull the head, measure the thickness, measure valve height and than repair any damaged valves and guides. When you install the belt and tension it are just setting the tension properly? Did you measure the clearance, or can you at least put the pin back in after you remove it? The engine shouldn't really be any harder at all to turn with the head on and plugs out than with the head off. If you try to turn it fast than there will be some resistance from air not being able to move thru the plug holes as fast as you are forcing it, but it won't be noticeable if you turn it slow. Also never turn the engine counter clockwise after you have timed it, this will take pressure off the tensioner and can cause the engine to skip time.
 
^^ Listen to this guy

This is some scary stuff, freaks me out on the stroker build I'm doing for a friend but I'm pretty sure I have everything right...

wait 7 years holy crap you are determined... I think after the first time I would have got someone more knowledgeable in to help
 
Last edited:
Definitely take Bryan's advice, because it seems like for the most part you have been trying to eye everything/hold your thumb to the wind. Time to start taking measurements and getting a lot more into details.
 
Man four times hope you figure that issue out, i wouldnt have the patience to keep dealing with it myself.
 
The 2g timing plate is totally different with a different timing mark location.

Everything I have done to this car was after long research, not much "guessing" involved, but I think you did just hit on the guess I made wrong. Here's my theory:

The first build I timed everything right. It ran fine, but I forgot the woodruf key, so timing probably jumped a lot when the crank sprocket eventually turned on the crank end.

Second build, still no key and crank bolt was not correctly torqued: Instant bent valves on cranking

Third Build, key in and crank bolt torqued right: Where I am now

IIRC the timing plate was re-used because my research showed that you can reuse it for a 6bolt swap if you trim the "ears" off it. Since there was no key in the keyway before, I was able to put the wrong timing plate on correctly (if that makes sense).

Now, with the keyway setup and the plate being integral to the keyway, my timing marks are pointing somewhere else. I thought I made up for this by making new marks on the modified plate, but I could have made them wrong. I aligned the timing mark with the one on the front case when the engine was at TDC.

Or it is valve-height or head thickness, which I won't know until it is torn down again. Glad I got the cheapo valves
 
Everything I have done to this car was after long research, not much "guessing" involved, but I think you did just hit on the guess I made wrong. Here's my theory:

The first build I timed everything right. It ran fine, but I forgot the woodruf key, so timing probably jumped a lot when the crank sprocket eventually turned on the crank end.

Second build, still no key and crank bolt was not correctly torqued: Instant bent valves on cranking

Third Build, key in and crank bolt torqued right: Where I am now

IIRC the timing plate was re-used because my research showed that you can reuse it for a 6bolt swap if you trim the "ears" off it. Since there was no key in the keyway before, I was able to put the wrong timing plate on correctly (if that makes sense).

Now, with the keyway setup and the plate being integral to the keyway, my timing marks are pointing somewhere else. I thought I made up for this by making new marks on the modified plate, but I could have made them wrong. I aligned the timing mark with the one on the front case when the engine was at TDC.

Or it is valve-height or head thickness, which I won't know until it is torn down again. Glad I got the cheapo valves

The way you marked the plate makes sense to me. Who assembled the head? If a machine shop did it, they should provide you with numbers on valve tip height and seat pressure after assembly. The springs should have included a spec sheet with targets for those variables. I know you said cheap valves, but which manufacturer specifically?
 
Head thickness not likely, as all of the normal valve to pistons clearance would have to be shave off and the tips of your valves would be way above the head surface.
Valve tip height, not likely.
Spring pressure less likely.
Valves whether cheap or expensive are going to bend if hit by piston.
Go back to your plate and make sure all reference points match.
 
Engnbldr valves, the same kind everyone else uses.

Nothing obviously wrong under the valve cover. Looks like some slightly bent valves again.

Not much can be learned until I at least get the timing covers off and I can check my timing marks on the plate. Will report back results then.
 
Sounds like the wrong firing order.
 
I've tried every firing order I could think of. The stock 2g is the correct one, and it does not misfire, but it also doesn't start. Cranks fine without plugs, with plugs it will try to start for about 5 seconds then stops cranking.

A cold compression test showed cylinders 1-4 as 165 - 150 - 180 - 180.

I tried adding oil to see if it was the rings or valves where compression was leaking on 1 and 2, but I think I added too much. The next test yielded 250psi+ before I stopped cranking. Have to wait for the oil to leak down before re-testing I guess.
 
Oh yea you effectively raised the compression ratio of that cylinder. Oil is essentially non compressible and way too much can hydro lock it. I think it's time to take a step by step approach to diagnosing this. Your on the right track with a compression test, I guess fuel and spark are next. And don't think that just because your car ran before, that it couldn't be your ecu, cas, mpi relay, ptt etc. Sometimes it's murphy's law and stuff goes at the worst time.
 
Support Vendors who Support the DSM Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Innovation Products Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications MyMitsubishiStore.com RixRacing RockAuto RTM Racing STM Tuned

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Back
Top