Zero compression....video and pics

[sproggy]

My truck was running fine until suddenly it wasn't. I limped back home and discovered that the two middle cylinders were not firing thought they had spark. Today I did a compression test and the numbers are all 160 and over except for those two cylinders that have zero compression. The gauge did not budge and instead the engine made a different kind of noise from when testing the others. What can I conclude from this? I thought perhaps the head gasket between the two has blown? And then I saw the hold in my manifold which I have included in the photos. Was there something screwed in here that has fallen off/out? I plugged it with my finger when running engine and did not notice any change or feel any suction but it does look like there are marks on the intake from a bolt. Any takers on this one?

Here's a vid of the compression test:

Thank you, Sproggy

 

[copperline]

Leak down test. Remove valve cover and chdck for stuck valves.

 

[stevebradford]

Remove valve cover and chdck for stuck valves.

Seems unlikely to me that valves would get stuck in two cylinders beside each other all of the sudden.

Logically the head gasket has failed between the two cylinders.

 

[sproggy]

I'm trying to do a leak down test but the damn kit from Autozone doesn't fit the radiator mouth.

 

[73FJ40]

The hole in the intake manifold is for a bolt to fasten the OEM exhaust manifold to the bottom of the intake manifold.

It appears you have headers. Ergo, no need for the bolt.

 

[SteveH]

I'm trying to do a leak down test but the damn kit from Autozone doesn't fit the radiator mouth.

Try pressurizing the cylinders with your compression tester hose (schraeder valve removed) and see if you get bubbles in the radiator. Check your valve lash on those two cylinders - that should tell you a lot, too.

 

[sproggy]

I popped the valve cover and valves appear to be doing some grand valving so no issue there.

 

[sproggy]

I'm trying to do a leak down test but the damn kit from Autozone doesn't fit the radiator mouth.

Try pressurizing the cylinders with your compression tester hose (schraeder valve removed) and see if you get bubbles in the radiator. Check your valve lash on those two cylinders - that should tell you a lot, too.

What's valve lash?

 

[sproggy]

The hole in the intake manifold is for a bolt to fasten the OEM exhaust manifold to the bottom of the intake manifold.

It appears you have headers. Ergo, no need for the bolt.

Good! Thanks!

 

[sproggy]

The hole in the intake manifold is for a bolt to fasten the OEM exhaust manifold to the bottom of the intake manifold.

It appears you have headers. Ergo, no need for the bolt.

Good! Thanks!

 

[SteveH]

Valve lash is the clearance (in thousandths of an inch) that you can measure and set that lets your valves open and shut properly. Without any lash, the valve may be held open, giving you poor or no compression. Set too loosely, the valve train will be noisy and performance is lost. The clearance is measured under the valve cover, between the rocker arm tip and valve-thingie (the technical term).

The Haynes manual (and OEM service manual) give good adjusting procedures. It's part of a full 'tune up' on vehicles like ours. And don't trust 'Brakes Plus' to do this - you need to learn and do it yourself. Basically - you set the engine at TDC, engine full-hot, and adjust 6 of the valves. You then turn engine over 360 degrees and do the other 6 valves. You need feeler gauges and a regular socket set and open-end wrenches to do this task.

In your case, if valves have lash they should not, then the valves are 'stuck open' or there is some other valve train issue.

 

[sproggy]

That is a good quick lesson in lash and adjusting the valves and def something I would like to get at and WILL get at eventually so thanks. I assume the lash would have to be way way off to give no compression at all, yes? I mean, the gauge is not even moving on both of those two cylinders. I should add, as I've mentioned in other posts, that I have suspected that I was burning coolant as I had white smoke out of the exhaust off and on for a while now. Having blown out the gasket between these two cylinders fits with that, I think.

Back to a few more tests!

 

[SteveH]

If you truly have almost no compression in adjacent cylinders, it's likely a blown head gasket or a big meltdown - not just 'valves out of adjustment'. But, even if you rebuild the engine or replace the head gasket, you WILL want to know how to adjust your valves. You'll get some man points when you mention it in passing to your co-workers who aren't sure what a valve is, or why it would need adjusting.

 

[JohnnyC]

Blown head gasket

Between the three and four it’s not very wide... it goes

 

[sproggy]

If blown head gasket, what all am I going to need to fix this: head gasket, header/intake manifold gasket, mill the head, a friend or hoist to get the head off....def PB Blaster because I've taken to drinking that stuff it's so good. I'm dreading taking off the headers as I remember they were a beeeech to get on...lot's 'o leaks, which explains the orange gasket seal around the manifold. My valve cover gasket was changed a year ago and in good shape.

 

[SteveH]

Let's add the word 'OEM' in front of 'head gasket'. Don't get a parts-store part, as you don't want to do this job twice. Don't be a hurry, and have the head checked for cracks, and you might as well have a valve job done. The head may not need to be milled. Replace the galley plug in the head (a machine shop will do this for cheap) and replace the valve stem seals. Read up on Mud about head gaskets, and you'll learn what you need to know.

 

[sproggy]

Let's add the word 'OEM' in front of 'head gasket'. Don't get a parts-store part, as you don't want to do this job twice. Don't be a hurry, and have the head checked for cracks, and you might as well have a valve job done. The head may not need to be milled. Replace the galley plug in the head (a machine shop will do this for cheap) and replace the valve stem seals. Read up on Mud about head gaskets, and you'll learn what you need to know.

Thanks, SteveH. How would I know if the head needs to be milled? I have a tendency to be quite nonchalant about tolerances as in I'll run my finger over the surface and think, "feels pretty smooth to me." I suppose I need to order this "galley plug" from somewhere? And I guess the valve stem seals? My compression is quite good on the other cylinders....160 to 165...even up to 170 on a couple turning over the engine about 8 turns.

 

[65swb45]

Are your head and your block the same color? Or put another way, does it look like the head may have been off once before?

If so, there is a slightly increased chance that the block itself may have developed a low spot between the cylinders that marginally seals for while with a fresh head gasket. I have seen this before. At least twice.

 

[sproggy]

Are your head and your block the same color? Or put another way, does it look like the head may have been off once before?

If so, there is a slightly increased chance that the block itself may have developed a low spot between the cylinders that marginally seals for while with a fresh head gasket. I have seen this before. At least twice.

I don't think it's ever been off. I bought it in 1985 and have had it since. Looking at it, I can't even tell (hardly) where the block and head meet. Just looks like one piece. Do you sell the required gaskets, Mark? I'm actually not going to be able to get to fixing it probably for at least a month as I have to leave the country tomorrow but would like to have everything ready to pop in when I get back. From one site, it seems the OEM gasket is no more so I can't follow SteveH's advice on using OEM...

 

[FJ40newmechanic]

If you have the 2F Engine Repair book, there is a flatness test you can do with a sturdy metal straight edge that you know is true and some feeler gauges to check the amount of bend in the head, and there is a gap spec you need to be within. If you are good there, then the book says you don't need to machine it. If you don't have the book, let me know and I can look up the gap spec for you. I was reading it last night in preparation for working on my 2F.