Misfire in Cylinder 4

[coco26]

That looks like one or more of the belt guides came loose or was set too close to the belt and melted it from rubbing. Yikes

[dgoodhue]

That looks like one or more of the belt guides came loose or was set too close to the belt and melted it from rubbing. Yikes

 

The timing belt is a mess I agree that it looks to be interfering with the guides. If the intake cam was moved over a half of tooth, the exhaust cam would line up. The tensioner could be weak (or wasn't replace with the timing belt), the belt stretched, or it was installed a tooth off on the crank. Either way someone didn't install the timing belt properly and it need to be redone.

[SaskyGT]

Okay, finally got to removing the head. Boy do I like working on my dsm by a long shot. Anyways, here are some pictures. The one exhaust valve is smaller than the other, but can't what is going on. I want to say exhaust valve, but how do I check the rings?

 

When I did the leakdown I simply couldn't tell where the air was going. I had the filler cap off and nothing. Head by the exhaust tips, nothing.

[FLlegacy]

That is some contrast between those two pistons. Are sure it wasn't a headgasket leaking? And that one valve has definitely been changed but the other looks like it has pulled down into the valves seat considerably. I would remove the valve spring keepers and rotate the valves maybe one popped up is bent slightly.

[SaskyGT]

Pretty sure not a headgasket issue. No other symptoms - anti freeze or oil, nor leaking into other cylinder. Keep in mind that it hasn't been firing on cylinder 4 for about 1,000 km or so (could be more, po couldn't give me a concrete answer).

 

I'll try to find my spring compressor and take the valves out. The large one looks the same as cylinder 2 doesn't it?

 

Is there a way to determine the health of the piston rings at this stage?

[FLlegacy]

Pretty sure not a headgasket issue. No other symptoms - anti freeze or oil, nor leaking into other cylinder. Keep in mind that it hasn't been firing on cylinder 4 for about 1,000 km or so (could be more, po couldn't give me a concrete answer).

 

I'll try to find my spring compressor and take the valves out. The large one looks the same as cylinder 2 doesn't it?

 

Is there a way to determine the health of the piston rings at this stage?

 

Ring gap, and more importantly the piston to bore clearance. If the piston has a lot of clearance to the bore that will become more of an issue as it wears even more.

[SaskyGT]

To measure, do I just bring the cylinder tdc and use a feeler gauge? The most I have ever done with piston and cylinders is honing a shortblock 350 back in the day so this is getting beyond what I have experience in.

[FLlegacy]

To measure, do I just bring the cylinder tdc and use a feeler gauge? The most I have ever done with piston and cylinders is honing a shortblock 350 back in the day so this is getting beyond what I have experience in.

 

Piston to bore clearance you would need a bore gauge and micrometer, ring gap you could use a feeler gauge, just remove the top ring and place it in the bore square to the deck and insert the feeler gauge in the ring gap.

[FLlegacy]

If you remove the piston you will see the wear or lack thereof on the top and bottom of the piston skirt, as they tend to rock up and down if they are too loose in the bore.

[SaskyGT]

I talked to our head mechanic and his opinion was the cylinder looks fine, the cross hatching is still present and without any scoring, he figures there isn't anything too wrong there. In any case, at this deep into the engine, can I simply unbolt the rod, take the piston out and take a look? If it is fine, put it back in and bolt it up again? Can I get it out after taking off the oil pan?

 

Anywho, did a liquid leak test of the exhaust valves with isoprophyl alcohol and it just poured passed that smaller valve. Not as fast as I was putting it in, but definitely more than a seep. I think I may lucked out and just got a bad repair job on an exhaust valve. I'm waiting for my spring compressor to get back to me, hopefully the valve seat isn't too far gone.

[Justen1987]

I think the bottom end looks fine. the pistons look different because of the misfire, unburnt fuel cleaning the one. your exhaust valves are for sure junk and the source of your misfire. my theory for the valve failure on these engines is normal wear causing the lash to get too tight and the valve doesn't seat properly to transfer the heat. so if your just trying to get by maching only one head, make sure you check the lash on the other bank

[SaskyGT]

Both heads are off and at the machine shop. When I get the heads back on I'm going to pressure test that cylinder again.

[dgoodhue]

Anywho, did a liquid leak test of the exhaust valves with isoprophyl alcohol and it just poured passed that smaller valve. Not as fast as I was putting it in, but definitely more than a seep. I think I may lucked out and just got a bad repair job on an exhaust valve.

 

The valves on these EJ can stretch and the valve lash eventually ends up being zero or the valve being slight open, which leads to a burnt valve. It looks like you caught this one in time before got too bad. This seem like this happen on 100% stock cars and I wonder if its related to the stock tune.

 

I suspect that combination of the timing being off a tooth and valve not being 100% sealed is what cause your engine to run so poorly. If it hadn't skipped a tooth, you may have not known about issue until more valve damage was done.

[SaskyGT]

So bringing the compression issue to an end.

 

Machine shop replaced 3 exhaust valves, I got the heads back on and did a leak down test, all show fantastic numbers.

 

Now if I was competent, I wouldn't have needed to order brand new AVCS exhaust cams. Spent the last week reading about what I should have done and when I went to go clean them, found out that my pins have been bent.

 

When the gears arrive, I should have this guy assembled this weekend (finally!)

 

Has anybody re-pinned the gears and had luck? Or tightened the cam gear down without the spring, holding the hub in place another way, then install the spring once it is all tight? With the bolt squeezing everything together, is there any way that hub would move?