Low compression on 2 cylinders

[jdm9221]

So my car is a 6 bolt block with a 7 bolt head. I was running 19lbs and blew the head gasket. Before the head gasket failure the car was compression tested and ran 140 across the board. After tearing it all down I had the deck hot tanked,and resurfaced (shaved .08) the head is perfectly straight, I put in a fresh new felpro permatourqe and used my arp head studs, I had a guy who's been building DSM's come over to do the timing and we started the car. It ran but not great, we shut it off and when I came back this morning it wouldn't start. I ran a compression test(wot, yes the engine was cold, it won't start) cylinder 1&2 tested 138. 3&4 (where the head gasket blew) tested both at 98 even after adding oil. What are my possible damages? I haven't done a leak down test yet?is it possible that I have damage to the block? I shut the car off as soon as i first had problems and every gasket from the head up is brand new. Any opinion helps, im just lost now. I did bleed the lifters but the head was but vaccum checked

 

[jdm9221]

Had the HEAD* hot tanked and resurfaced

 

[jdm9221]

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

Pictures of the rebuild and bad gasket between 3 and 4. Nothing looked off when putting it back together

 

[boostdawd]

Did u check the valves before installing the head back? Poured water and let it sit to see if it leaked?

Double check your mechanical timing.

 

[jdm9221]

I didn't check the valves. Timing wouldn't cause only 2 cylinders to be low

 

[jdm9221]

Anyone else?

 

[A Sharp]

Leakdown test.

 

[jdm9221]

Going to run one as soon as I get the starter back on. What are my possibilities looking like damage wise. A friend mentioned block damage or it being warped which I doubt, I'm hoping on the valves needing reseated

 

[SasaniFab]

Going to run one as soon as I get the starter back on. What are my possibilities looking like damage wise. A friend mentioned block damage or it being warped which I doubt, I'm hoping on the valves needing reseated

That head was resurfaced? It's looks Ruff to me. Did you check the block with a straight edge? Your not using a mls type gasket correct? If your mechical timing is dead on and your surfaces are flat you could of cracked a ring land. If the head was hottanked then the head was completely broken down and new valve seals were installed yes? Seems odd that the cylinders that had the gasket failure are still low after a new gasket. Get that leakdown test don't. You might of damaged the engine .

 

[SasaniFab]

In the picture is looks like there are grooves in the cylinder walls? Was this the case?

 

[jdm9221]

They aren't groves they're cross mark from 40k ago when the engine was honed out, and new album e seals weren't installed

 

[motomattx]

First, how sure are you that you originally had a blown head gasket? 19 pounds with arp or even stock bolts shouldnt blow a head gasket, in your picture I dont see evidence of a blown gasket, what I am seeing is missing material from outside the fire ring that stuck to the block or head when you pulled the head off, a blown gasket generally has the ring melted in spots, what I'm getting at is that you might have something other than a gasket issue from the begining and it wasnt properly diagnosed, a leak down test is almost your only hope at this stage, broken ringlands are a possibility if it was knocking. Also maybe there is part of the gasket thats damaged that I cant see from the picture and it WAS bad, but it looks like the machine shop might have machined that head with the valves installed? if they did the intake valves are likely damaged now.

 

[jdm9221]

No knocking and it was running great til I got air in the coolant system. It overheated and I let it cool and topped it off. Drove it for 3 day and there's oil in my coolant and my oil is watered down. There was water on top of my pistons when I pulled the head

 

[jdm9221]

Also it won't let me edit my earlier comment, they didn't pressure check it and new valve seals weren't installed

 

[kmetiuk]

Did u check the valves before installing the head back? Poured water and let it sit to see if it leaked?

Double check your mechanical timing.

^^^ This. If your engine ran on first startup but roughly then my money is on the timing belt if off a bit. Not saying that is your issue with the low comp, but it's VERY likely that is why it ran rough and then wouldn't start the next day. Classic tell tale signs your timing belt if off a notch or 2.

That being said, did you check the valves doing a hydro test while the head was off the car?

Super easy test and will show whats leaking very quick. I'm currently doing that exact test this morning to check if my new Supertech valves/guides and valve seats are bang on. SURPRISE their not as I tested them last night before shutting it down for the night....2 tiny leaks and 2 big ones to fix and then re hydro test. I'm not even gonna bother putting the head on untill the valves pass the hydro test....whats the point if I know its leaking right? This is a MUST do if you have the head off. Water is cheap and test takes 10 seconds to set up the test and see the leaks.

In the picture is looks like there are grooves in the cylinder walls? Was this the case?

They aren't groves they're cross mark from 40k ago when the engine was honed out, and new album e seals weren't installed

What @amsrn13 is talking about is this:

You must be logged in to view this image or video.

We can clearly see something that doesn't belong.....looks like a wide chunk of something is fuuucking your cylinder wall up. Could be old gasket that fell in there during tear down, carbon build up making the piston rings stick, or worse...dirt/sand/a rock.

I would recommend (you really should) pulling the pistons and checking that cylinder wall man. You have something really bad going on there....that is NOT cross hatching as it is clearly destroying the cross hatch underneath it and likely fuuucking your piston skirt up really good.

I didn't check the valves. Timing wouldn't cause only 2 cylinders to be low

If you have the head off I would recommend doing every "while I'm in there" check that you can do for free....or even cheap. You're not gonna pull the head again for a while so I would mos def perform some basic checks such as hydro test the valves (with springs in and cams out).

Past that, it IS possible for the timing belt being off and affect compression. Your valves are not 100% the same height which affects valve train geometry.....I know b/c I am building my head and have blueprinted everything coming out and going in. Due to this difference it is *possible* for your timing to be off a tooth and have the valves slightly close/open ahead of another cylinder giving you a variance between compression results.

Possible, but in this case who knows. What I can say with confidence is you have some serious looking cylinder wall damage. With slightly less confidence it sounds like your timing belt is off a tooth or 2.

 

[jdm9221]

I can have him triple check timing but I don't see how it could affect the 2 cylinders right next go each other. It also starts now but is just running super rich because I just put in an evo ecu and haven't adjusted it. I see the maris your talking about but that's wasn't the cylinder affected by the head gasket and it compression tested at 150

 

[motomattx]

No knocking and it was running great til I got air in the coolant system. It overheated and I let it cool and topped it off. Drove it for 3 day and there's oil in my coolant and my oil is watered down. There was water on top of my pistons when I pulled the head

Ok, then it wasnt losing compression, it just had coolant leaking in from somewhere, in which case I would be on the side that the head or block wasnt straight from the begining and most likely was the head, I didnt care if he put new valves in rather what I was saying is that if he machined the head without removing the valves then he easily could have damaged the intake valves in the process, PLUS machining debris cant be cleaned out from the valves and will end up in the cylinders.

 

[jdm9221]

The head was machined .008 and was checked and level however the valves weren't removed

 

[motomattx]

The head was machined .008 and was checked and level however the valves weren't removed

That right there bothers me for the reasons mentioned, also .008" is alot to remove at one single machining from just the head, how sure are you that the valves didnt contact the pistons since they are now sitting closer to them?

 

[jdm9221]

When I got the head back he knocked one of the valves a tiny amount, now that I think about it that is on one of the cylinders that's low. I was told it wouldn't be a problem tho so I put it all back together

 

[jdm9221]

Knicked* it had a shiny minimal flat spot

 

[SOADweskey]

I think you need a better machine shop. 1. As stated it should never have been surfaced with the valves installed. 2. Looking at the picture of the head and yellow paper, it is clear that the head was never hot tanked as the paper states. If it were hot tanked then the combustion chambers would also be clean and not just the gasket surface.

 

[jdm9221]

"Tank head". It says it was hot tanked. The place has been around since 1968 I figure they probably knew what they were doing

 

[kmetiuk]

If you switched ECU's and now it runs then may be your timing is on then? I dunno....I'd still check timing but it sounds like that is no longer an issue.

Coolant on the pistons while pulling the head is just from it leaking out of the head as you lift it. Pretty normal. If you were burning coolant you woulda got a huge cloud of white smoke out the exhaust.

When I got the head back he knocked one of the valves a tiny amount, now that I think about it that is on one of the cylinders that's low. I was told it wouldn't be a problem tho so I put it all back together

Whoa....he machined the head WITH the valves in AND knicked a valve?!?! I don't even understand how you could expect to machine a head down 0.008" on a 4G63 head without knowing you were gonna hit the valves. I mean they are barely recessed enough on a virgin head (if at all). For example my head has been decked down once around ~0.001-0.002 (according to the indicator spots) and I am doing a valve job now. 1 of my valves is SUPER recessed (gotta tip the valve ~0.040") and would totally allow you to deck the head with it in. The valve right next to it sticks out past the head enough where I know for sure it will get knicked if left in. Can't set it on a table as it will wobble on the valves that stick out. Checking the valve install height and they are all within spec except for the one I need to tip. It really depends on the head and valves and is unique to each motor.

Honestly, that is where I would start. Pull the whole valve train apart and check that all your guides are still smooth inside and undamaged...I'd be worried that knick forced the valve into the guide and damaged it. Then check you don't have a bent valve (pretty unlikely). Then CLEEEEEEEEAN!!!!! I'd be soooooooooooo worried about machining chips in the valve seat/ports that I'd pull it apart JUST to clean it. Reassemble and do a hydro test (watch jafromobile vid 102 on youtube).


Also the seal you should hydro test is the seal at the seat in the combustion chamber....not the "rubber" stem seal at the top of the valve near the cam

IMPORTANT: if he knicked the valve then it likely was into the margin area of the valve. There are min values that this margin can be (check the FSM for value) and depending on how knicked it is then you are gonna need a new valve there if its past the margin.

Also I can see from the pic of the head that there are at least 3 valves with "shiny" spots where the carbon was removed during machining.

You must be logged in to view this image or video.

"Tank head". It says it was hot tanked. The place has been around since 1968 I figure they probably knew what they were doing

Maybe its been there since 1968....but the guy running the mill on the day your head went through may have only been there for a week....or he was being taught on the machine that day....who knows. Either way, you don't machining a head with valves in and knick a valve and then tell the customer "it'll be okay".


And as @SOADweskey said....hot tanking would have cleaned ALL the carbon out of the combustion chambers....they would be bare metal looking and not full of soot as we can clearly see., Hot tanking is LITEWRALLY to clean all that shiiit off...which yours still has on it....which means no hot tanking performed.

ALSO I believe you cannot actually hot tank an aluminium head as the caustic solution will eat the aluminium. The local shops around here even have that on their prcing list...hot tank (iron only). For alumnum they jet wash/steam clean them...which gets them equally as clean as a hot tank.

 

[jdm9221]

So at this point should I just be looking for a new head? The ecu was In when it first started as well as when it didn't start. I also compression tested it after I blew the gasket and before I took it apart and the compression on the 2 cylinders was low then