Bringing this m20 back to life

[MrBurgundy]

Well, compression can also leak from the piston rings or valves. We do a "wet" test to check pressure difference on a cylinder with low compression. When a cylinder shows low compression on a dry test, and it increases with a wet test, it points towards worn piston rings. Also, a leak down test is a great way to check the rings AND the valves.

To perform a leak down test, you set the cylinder to TDC, so all the valves are closed, and inject compressed air into the cylinder. Then, you can hear if air is escaping from the tail pipe, intake or oil filler cap.

at this point, I would just change all the rings and send the head to a shop to see if anything is wrong.

[mbonanni]

Bringing this m20 back to life

Im going to put the head back on with a new gasket and new bolts I've got lying around and go through a dry and wet compression test, and I will probably do a leak down test as well. If that shows the motor is toast ill throw in a 2.7i Ive got lying around and rebuild this one.

[mbonanni]

Bringing this m20 back to life

Took a second look at the head from a different angle and found this, bent exhaust valve on cyl #2

[MrBurgundy]

Nice, one step closer to getting this thing running right

[mbonanni]

Bringing this m20 back to life

Picked up my spare head, this thing was cleaned, pressure tested, decked, supposedly new valve stems and lapped valves. Ive also got new manifold gaskets, valve cover gasket, and intake gaskets.



I also prepped the block and cleaned the pistons. I found that piston #1 seems a little rounded down, wonder what this could be from.





And because I like everything clean I spent a lil time on the intake manifold as well as a few other parts not pictured




I'll be putting it together tomorrow, does anyone use gasket sealer or something when doing the head gasket?

[zaq123]

could it be that #1 piston was hitting the head? Any marks on the head? Put #1 just past TDC (begging of down stroke), push down on the piston with the wooden dowel (hammer handle) and note any excessive movement. Maybe rod bearings are shot and there is too much play. Some folks use copper spray. I do not use anything as it's know fact that ketones in the spray reacts with viton on the head gasket. Surface prep is the key (straight, true and clean).

Also you didn't rally have to clean your pistons that well. They didn't look bad at all from you pictures. Since you did, hopefully it wasn't done with a scotch brite.

[mbonanni]

It is totally possible that piston #1 was hitting the head, but wouldnt that bend valves? I already put the head back on so I cannot check the play in the rod bearings. I installed the head gasket with a coating of Permatex copper spray because I had weird feelings about this gasket, I prepped the surfaces pretty damn well I would say, so hoping for the best.

It was not with a scotch brite pad.

After getting the head on I did a compression test and got 65 across the board, could this be because it is cold, and hasnt been run for a bit? I didnt get the chance to do a wet test, but will do it asap.

I also found a wire completely corroded in my harness so I removed that and will be repairing it.

[ForcedFirebird]

Piston will hit the head before the valve. If you have low comp on all, check your belt timing.

[mbonanni]

Learning a lot here gentlemen, thanks!

So I took the gear off again, third time [emoji30], and was able to get the other one on. I found my old phone and took a few pics of the gear and pin, this thing had to have put my timing off 10-20 degrees like someone mentioned. To install the good gear I had to remove the pin from the camshaft. Pics suck I know but it is what it is, sorry if they're big. I also had to tear the harness completely apart due to the wire corrosion, its an orange one idk if you can see it. I'll probably fix this tomorrow if I can find a matching connector.


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[zaq123]

how did you figure that your timing was off by 10-20 degrees? with the dial gauge or marks didn't line up on gears and you just guessed it?
If your timing marks don't line up....why? someone shaved the head/block prior? Maybe someone rounded that piston prior as well, when they tried to clean it? You can roughly check your rod bearings from the bottom, if you drop the oil pan. Bottom end of the rod should have some side to side play (axial on the crank) but no noticeable radial play. The only difference in checking it from the bottom, piston should be in right before TDC position when you put wooden dowel on it. Obviously very crude test but the idea is pretty self explanatory: Almost all bearing clearance is on the rod cup side on the up stroke before TDC and on the rod side on the down stroke after TDC. Normal bearing clearance is so small, you can't feel any movement and definitely shouldn't hear any clunking.
Also you can check P to H clearance from the spark plug hole with a long piece of thin solder. Just make sure P is right before TDC with valves almost closed, put a bend in the solder so it's pointing to about 2 o'clock and the bend is long enough to reach the wall, put the solder in, bring piston just past TDC, back the crank out, CCW and remove the solder. Measure.
Don't spin the crank 180' or much past TDC as the solder will tangle with the valve opening. If the solder get squished so much that it breaks off or something, don't worry, it means your clearance is not near what it should be and the head needs to come off anyway for a thicker gasket. 2mm solder wire can get squished way way below min recommended PtoV clearance (about 1mm) without breaking.

[ForcedFirebird]

how did you figure that your timing was off by 10-20 degrees?

Take a close look at the cam gear in the pic above ;)

I mentioned his cam timing was off with the compression numbers, he pulled the gear and saw the damage...

[zaq123]

Take a close look at the cam gear in the pic above ;)
.

Did someone modified the gear? From the pic, I first thought OEM drilled it in the different than pre-stamped spot to actually time it "properly". So I take that this gear/head wasn't originally installed on this car...

[mbonanni]

Correct, I pulled the bad gear off of my spare "rebuilt" head. I never ran the car with the bad gear, only did a compression test with it installed. Regardless, I got the car back together yesterday and it runs great besides a small vac leak that causes the idle to drop when returning to idle.


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