Compression testing by hand cranking

[BrutalSlammingMetal]

Before I begin I'd like to apologize in advance for any protocol I may be breaking - I have just joined and did some searching.

This question is about a 2005 Ford Explorer Sport Trac. I'll attempt to provide some pertinent details:

• V6 SOHC 4.0L
• 187k miles
• I bought it about a year ago with 180k miles
• The engine has been pulled and is sitting on the shop floor
• I am a novice DIY auto mechanic, so not really an auto mechanic. I do work in a field that requires me to be handy with a wrench
• I can't decide if I'm trying to do this fix for as cheap as possible or not

The engine started sounding bad after this past fall's first real cold weather, but no change in performance, gas milage or oil usage was noticed so I was merely curious rather than vigilant. The sound I was getting I now know to be the timing chain. This was the status quo for about 6 months. The truck is my daily driver in our fair city; I drive about 30 miles a day.

The right side timing chain jumped some teeth, chewed its guides up, and blew a nice hole in the valve cover. The tensioner is a little rough but I bought a new one and the new one doesn't appear to function too differently than the used one. On the one hand, I think I could save $40 by leaving the old one in. On the other hand, this seems like it could potentially be a cause of the whole issue. What do you think?

The sprockets on the right side camshaft and rear jack shaft don't look too unusual for having 180k+ miles on them. Same with the chain. But those will be replaced. Was not planning on changing the left side or front timing chain/sprockets. Your thoughts?

We have on pretty good authority that, sometimes when the timing chain goes, it can cause the pistons to damage the valves. So we are trying to figure out if the valves are still good. That finally getting to the subject line of the post: what values should we see when we perform manual compression testing? Yesterday we achieved 10-25 PSI on five of the cylinders but close to 50 PSI on the sixth. After some reflection we realized we need to squirt some oil in the cylinders and redo the tests. But what numbers should we see given the above info? I don't want to rig up the stater or other electric motor to turn the engine over because that would be time consuming, but I suppose I will if it's the only definitive way to test the valves.

Last question for now: what other components should I consider changing while the engine is easily accessible?

This forum has already proven to be very helpful during this project. Thanks for any help or insight you are willing to provide.

 

[Tech By Trade]

get a hold of a leak down compression tester if you cant turn it over, you are way low. 145 I do believe is what you want, but the biggest thing is to be over 100 and within 25 psi of each cylinder.

 

[96firephoenix]

I am a novice DIY auto mechanic, so not really an auto mechanic. I do work in a field that requires me to be handy with a wrench

Take it from an experienced DIY auto mechanic, you do not want to rebuild this engine if you are only "handy with a wrench," this is not a novice-level project. If you want to jump in on rebuilding an engine, get a carbed Chevy 350 - they are simple as ****. This is not.

I mean this with out malice: Replacing just one timing chain set on an engine with 187K miles is utterly foolish. You will be replacing the other one sooner, rather than later. Especially given that the passenger side one needs to have the engine separated from the transmission to change, you might as well change it now while you've got it apart.

If one cassette or chain is broken, I would consider the whole engine to be gacked. Consider this: you've got timing chain bits all through that engine, and probably . You've got to do an almost complete tear-down (remove everything but the pistons and heads) to make sure that you got all of it out and there's not a link of chain, or piece of guide plastic or spring leaf somewhere, waiting to get into moving parts and toast your engine. At the very least, you have to take the oil pan off and scrape out the gunk.

The good news is, your heads are probably ok.

After starting in own truck with a bad 4.0, I abandoned my plans to rebuild my 4.0 when I realized that it was only about $500 that I'd be saving vs. a remanufactured engine after all the little **** crept in like parts that broke on tear-down.

If you do go this route and need parts, hit me up, I've got 2 stripped engines in my garage right now, lol. I think I've got 3 sets of valve covers if you need them.

 

[BrutalSlammingMetal]

get a hold of a leak down compression tester if you cant turn it over, you are way low. 145 I do believe is what you want, but the biggest thing is to be over 100 and within 25 psi of each cylinder.

Thanks man.

 

[BrutalSlammingMetal]

Take it from an experienced DIY auto mechanic, you do not want to rebuild this engine if you are only "handy with a wrench," this is not a novice-level project. If you want to jump in on rebuilding an engine, get a carbed Chevy 350 - they are simple as ****. This is not.

I mean this with out malice: Replacing just one timing chain set on an engine with 187K miles is utterly foolish. You will be replacing the other one sooner, rather than later. Especially given that the passenger side one needs to have the engine separated from the transmission to change, you might as well change it now while you've got it apart.

If one cassette or chain is broken, I would consider the whole engine to be gacked. Consider this: you've got timing chain bits all through that engine, and probably . You've got to do an almost complete tear-down (remove everything but the pistons and heads) to make sure that you got all of it out and there's not a link of chain, or piece of guide plastic or spring leaf somewhere, waiting to get into moving parts and toast your engine. At the very least, you have to take the oil pan off and scrape out the gunk.

The good news is, your heads are probably ok.

After starting in own truck with a bad 4.0, I abandoned my plans to rebuild my 4.0 when I realized that it was only about $500 that I'd be saving vs. a remanufactured engine after all the little **** crept in like parts that broke on tear-down.

If you do go this route and need parts, hit me up, I've got 2 stripped engines in my garage right now, lol. I think I've got 3 sets of valve covers if you need them.

Cheers man. I've got some thinking to do.

 

[Tech By Trade]

It is a big job, but it can be done. Did mine over a couple months around christmas a couple years ago. If the valves did hit the pistons I wouldn't waste my time. I got lucky and the cassettes detonated but the chain never jumped.

 

[BrutalSlammingMetal]

It is a big job, but it can be done. Did mine over a couple months around christmas a couple years ago. If the valves did hit the pistons I wouldn't waste my time. I got lucky and the cassettes detonated but the chain never jumped.

Thank you for your reply, Tech By Trade.

Do you mean the plastic guides were destroyed, but the chain, tensioner etc. were ok?

Just put the compression chambers under 120ish psi, and found that cylinders 3 and 4 do a good job of holding air but the rest permit a lot of air flow out of the cylinder. I conclude that the valves could need to be replaced.

So I'm going to pull the heads and take a look. But I interpret your post to mean you don't think it's a good idea to do this, if the pistons struck the valves, can you explain why? Whats the downside of having new valves, and one new timing chain?

Sorry if these are dumb questions. My motivation for pursuing the route of changing as little as possible is explained best by George Costanza, I'm currently "between opportunities" so I'm rich on time and low on cash.

 

[Tech By Trade]

The heads are pretty much disposable on these things. For the amount of labor and time involved in doing a rebuild, there are plenty of 4.0l sohc available in scrap. They came in mustangs, rangers, sport tracs, land rovers, and explorers, and any one will fit from 97 to 2010. they can be had for around a grand. It would be cheaper just to get one from a wrecker, replace the cassettes as a preventative measure and drop it in rather then screwing around machine shops. You just have to keep the old engine around, and strip it to a long block and swap all the components to the wrecker long block. Probably cheaper in the end too.

 

[BrutalSlammingMetal]

The heads are pretty much disposable on these things. For the amount of labor and time involved in doing a rebuild, there are plenty of 4.0l sohc available in scrap. They came in mustangs, rangers, sport tracs, land rovers, and explorers, and any one will fit from 97 to 2010. they can be had for around a grand. It would be cheaper just to get one from a wrecker, replace the cassettes as a preventative measure and drop it in rather then screwing around machine shops. You just have to keep the old engine around, and strip it to a long block and swap all the components to the wrecker long block. Probably cheaper in the end too.

OK good stuff man, thanks.

 

[96firephoenix]

So I'm going to pull the heads and take a look. But I interpret your post to mean you don't think it's a good idea to do this, if the pistons struck the valves, can you explain why? Whats the downside of having new valves, and one new timing chain?

The main reason is that if the pistons strike the valves, you usually have to replace the piston and the valves. replacing the valves requires re-seating them in the head, which is a machine-shop level job, not a novice-DIY-level job

The only real downside for only replacing one chain is what I said earlier: the other one is close to failure at this point as well, and you will be in the exact same spot on the opposite side of the engine.

Just put the compression chambers under 120ish psi, and found that cylinders 3 and 4 do a good job of holding air but the rest permit a lot of air flow out of the cylinder. I conclude that the valves could need to be replaced.

This won't be a good test because at any given time, only 2 cylinders will have the valves sealed. The other 4 are at some point of intake or exhaust with the valves unsealed.

 

[BrutalSlammingMetal]

This won't be a good test because at any given time, only 2 cylinders will have the valves sealed. The other 4 are at some point of intake or exhaust with the valves unsealed.

96firephoenix,

Thank you for sharing your experience with me. I agree I don't want to attempt any machining work.

Just want to ask for some clarification - I was thinking with the timing chains off and pumping the air through the spark plug port would result in checking leakage on the valves individually rather than jointly. Are the cylinders "plumbed" together?

Thanks again to all for participating in my thread.

 

[96firephoenix]

Just want to ask for some clarification - I was thinking with the timing chains off and pumping the air through the spark plug port would result in checking leakage on the valves individually rather than jointly. Are the cylinders "plumbed" together?

So when you test the compression by blowing air in, you are testing the whole cylinder: piston rings, valve seats, valve seals, and head gasket.

The intake and exhaust valves both open directly to the cylinder, so if either one is open, the cylinder will not hold air. There is no way to test an individual valve on its own without taking the head off.

Easy way to tell when the valves are closed is to pull off the valve cover, and rotate the engine until the lobes on the camshaft are both up. If it holds air in that configuration, then move on to the next one, but if it doesn't hold air, you only know that the cylinder (EDIT: maintains should be has lost) compression - you don't know if it's the valves, the head gasket, the piston rings, or even a cracked head or block (not likely for the last 2, but still...)