'72 620 Head Gasket Replacement

[atkinson40]

Began pulling plugs to see if there was evidence of water in the cylinders and found the second cylinder back from the front of the truck was flooded with water. That's enough for me to start the HG repalcement.

 

I've done this job about 20 years ago on the same type vehicle along with changing the rings. I still have the scar from when I broke the hex allen trying to get off one of the head bolts. :blink: Hopefully I wont have to change the rings on this truck. If I remember right I had to remove the oil pan to get the retainers off the piston arms to get the pistons out. Also I remember needing to use a tool to cut the little ring of carbon?? off the top of the cylinders where the old rings toped out in the cylinders. This supposedly kept the new rings from hitting that carbon ring and breaking. Here's a couple of shots before I start.

 

 

Question 1. What is this little gizmo that's been disconnected in the back/left engine compartment?

 

 

Also what is the item shown below? It seems to be a housing for a switch that went to the accelerator pedal.

 

 

OK I've removed the air cleaner, d-cap/wires and the valve cover.

 

 

I'm a certified neat freak so if the truck seems to get cleaner as I go along that's the reason. Here's my favorite tool.:)

 

 

Tommorrow I'll remove the gas pump, and thermostat housing, and lossen and try to move the intake/exhaust manifolds back and out of the way. If I remember right, there might be clearance to leave them in the truck while I pull the head.

 

I also remember something about needing to rig something to keep the timing chain from falling down and the tensioner in place.

[banzai510(hainz)]

this will help.

http://www.guba.com/general/search?query=hainz&set=5&x=0&y=0

 

 

always set motor/head up to TDC zero on crank. so when you reinstall TDC will be your reference.

 

 

the throttle swithc is the 3rd gear switch mostly used for emission and 2nd set of points.It retards the ignition. Most times people disconnect the 2nd set of points or just pull the wire off and use the main set of points,the one with the big condensor on side of the distributor(dizzy).

 

 

the wooden block method is what is used to keep the chain from falling down but most importantly keeping the tensioner from pushing out and tightening the chain. Do you have this wooden block that is special shaped with a rope attached to pull it out? If you fuck up youll be pulling the front cover

 

 

Most of all. try looking looking at the intake gasket first and maybe replacing this. sometimes the intake/exhaust bolt get loose and it suck in water from the intake as there is a water passage hole from the manifold to the head to heat the carb up (keep from freezing in winter)

 

 

that box that is disconnected could be the choke relay since lokks like the other owner then to a pull cable manual set up.(dont worry about it)

Edited July 16, 2009 by banzai510(hainz)

[datsunaholic]

The relay that's disconnected in the corner is (was) the choke heater relay. It's disconnected because of the jerri-rigged choke setup (it USED to be an electric choke...). The switch-like thing by the accelerator cable might have been for the dual-point cut-in circuit, though I'm not certain.

[atkinson40]

I don't have a wooden block with something to pull it out. Can anyone tell me how to make and use it? Also I'll try the intake MF gasket first. That would be cool if that fixed the problem.

[datzenmike]

I wouldn't remove the pump or the thermostat housing unless I knew they were leaking and also needed a gasket. Leave on the head, they can only break the bolts off if you try to remove.

 

I never take the intake or exhaust manifolds off if just doing a head gasket. Just remove the down pipe and lift it all off together. Less work and less chance of stripping a nut or snapping a bolt.

[atkinson40]

Thanks Mike. Too late for intake manifold. I've already removed it. I may not be able to lift off the head without removing the exhaust manifold. I'll see.

 

 

I don't see any evidence of water leakage past the gasket under the intake manifold.

 

 

 

I going to try too track down a presssure gauge to check the cylinder pressures. I used to have one but I have grown kids and tools sometimes walk away.:)

[datzenmike]

I hear that!

[atkinson40]

One of my kids borrowed a pressure gauge and we did the test. From front to rear the readings were.

 

1. = 95psi:)

2. = 95psi:)

3. = 45psi:eek:

4. = 110psi:)

 

No way around it. Looks like HG blown. I've got everything removed from the head. What's the next step? How do I get the T Chain off that big honkin gear and keep the chain from falling down? TIA Kevin

[datzenmike]

Looks like #3 but over all that motor is getting tired. If compression is fairly close on all cylinders, like say 100, then it will run smooth. If not burning oil I'd drive it, but maybe plan on a new set of rings next year. Compression on a good motor should be 170 or higher.

[banzai510(hainz)]

http://shop.oreillyauto.com/productdetail.aspx?MfrCode=PBI&MfrPartNumber=648831&CategoryCode=3491.

 

 

brake the bolt loose on the cam sprocket. Vedio????????

make sure crank is at Zero

 

right before you pull the sprocket jam the TOOL/wedge down the front cover and drap chain over it.

 

Only way to make this Ezer is I come over and do it for you.

 

But its hard to get that sprocket back up.

 

also get a ink pen and mark the chainlink that is in the 2 oclock position with the dimple under it. this is so you dont get the chain off a link as you pulling the sprocket up and turning it.

[atkinson40]

Looks like #3 but over all that motor is getting tired. If compression is fairly close on all cylinders, like say 100, then it will run smooth. If not burning oil I'd drive it, but maybe plan on a new set of rings next year. Compression on a good motor should be 170 or higher.

 

Hmmm. I may decide to do rings now that I have it torn down. I'll look at them. Thanks Kevin

[atkinson40]

http://shop.oreillyauto.com/productdetail.aspx?MfrCode=PBI&MfrPartNumber=648831&CategoryCode=3491.

 

 

brake the bolt loose on the cam sprocket. Vedio????????

make sure crank is at Zero

 

right before you pull the sprocket jam the TOOL/wedge down the front cover and drap chain over it.

 

Only way to make this Ezer is I come over and do it for you.

 

But its hard to get that sprocket back up.

 

also get a ink pen and mark the chainlink that is in the 2 oclock position with the dimple under it. this is so you dont get the chain off a link as you pulling the sprocket up and turning it.

 

 

Thanks. I called Kragen and they'll special order the wedge for me. Kevin

[Bugeye]

Thanks. I called Kragen and they'll special order the wedge for me. Kevin

 

you can make one yourself out of a 2x4 and some rope

[Bleach]

it is best to use hardwood. Furniture grade wood for the wedge won't splinter or crush as easily. :)

[atkinson40]

you can make one yourself out of a 2x4 and some rope

 

 

Thanks Bugeye. If they were any more than $3.50 I would. May be a mute point if I have to do rings. Not sure if its required if I have to remove the front cover to do rings. I do remember being able to take off the oil pan and get the pistons out, but don't remember if I had to take off the front cover. Thanks kevin

[atkinson40]

Looks like #3 but over all that motor is getting tired. If compression is fairly close on all cylinders, like say 100, then it will run smooth. If not burning oil I'd drive it, but maybe plan on a new set of rings next year. Compression on a good motor should be 170 or higher.

 

 

Mike, Is there any way we could have done the compression check incorrectly? We used the Mac gauge that screws into the plug hole. I spun the engine while my kid held the gauge. There was water spewing out of a couple of cylinders. I didn't think this would affect the readings?

 

Also is there another reason the compression could be low? What about worn valves/valve seats? If there's any chance of needing to replace rings I'm going to do it while I've got the head off. Is there a way to definately determine that it needs rings beyound a compression check?

 

I don't know the history of oil usage on the vehicle. TIA Kevin

[datzenmike]

I have a screw in one and it's way better than holding it in by hand. You could do it a second time and if the readings are similar you probably got it right the first time. Do it with all plugs out and throttle propped open to get maximum readings. Try a few squirts oil in the test cylinder and crank it around a few times to distribute it on the rings. Retest that cylinder. If the compression jumps dramatically then the oil is sealing the bad rings.

 

A leak down test would show a percentage of compression loss. A reading of 20% loss is getting close, 30% loss would be serious enough for thinking about a ring job. A reading of under 10% is near impossible to get so 10-15% is good. Even 20% isn't too bad and a rebuild may not be worth the expense. These values are open to interpretation and are an indication that something may be wrong.

 

A leak down test can also be used to listen at the carb for hissing sound of air escaping past a bad intake valve or the exhaust down pipe for a bad exhaust valve. A hissing sound at the valve cover vent would indicate air leaking past the rings.

[atkinson40]

I have a screw in one and it's way better than holding it in by hand. You could do it a second time and if the readings are similar you probably got it right the first time. Do it with all plugs out and throttle propped open to get maximum readings. Try a few squirts oil in the test cylinder and crank it around a few times to distribute it on the rings. Retest that cylinder. If the compression jumps dramatically then the oil is sealing the bad rings.

 

A leak down test would show a percentage of compression loss. A reading of 20% loss is getting close, 30% loss would be serious enough for thinking about a ring job. A reading of under 10% is near impossible to get so 10-15% is good. Even 20% isn't too bad and a rebuild may not be worth the expense. These values are open to interpretation and are an indication that something may be wrong.

 

A leak down test can also be used to listen at the carb for hissing sound of air escaping past a bad intake valve or the exhaust down pipe for a bad exhaust valve. A hissing sound at the valve cover vent would indicate air leaking past the rings.

 

I had the intake and exhaust manifolds off the vehicle when I did the test. I had all spark plugs out. Would this affect the readings? Is there a visual way to look at the rings once I get the head off to determine if they're bad? Thanks kevin

[Buzzbomb]

Thanks. I called Kragen and they'll special order the wedge for me. Kevin

 

I'll vouch for this tool....I used one a few months ago when I did my head gasket in my L20B, and it was easily the best $4 I spent in a long time. There are no worries with getting the dimensions right, no worry about splinters, etc. You shove it in there, leave it, and take your time.

 

When I put my chain back on the sprocket, I had a helper push down on the chain tool so I could use all the slack in the chain to line my marks up. After I lined up the marks, I swung the sprocket/chain upwards and sideways to the cam dowel, and it went right on with no trouble.

 

That tool is totally worth it..This is more for those who find this thread when looking for head gasket only stuff. In your case, if you need to do more work, it's a moot point. Just use Hainz's great video to help you get all the valve train stuff lined up.

Edited July 18, 2009 by Buzzbomb

[datzenmike]

All you'll see with the head off is the cylinder wall. In bad cases the cylinder may be scratched or stained from blow-by but generally a smooth bore tells you little.

 

Manifolds off during a compression test is fine. Try squirting some oil on the plug hole and re testing. If the rings are worn, the oil will seal them and the readings will jump up. If no change, then the compression loss is somewhere else like the valve seats.

[atkinson40]

A bit of oil down the cylinders cause the compression numbers to jump so looks like rings needed also. There's another ring job thread in the "Engine Forum" so I'm going to continue this thread there also. Another perspective as I do the same job shouldn't hurt. Thanks Kevin