1997 1ton van, 318 engine rebuild or replace?

[draker]

Just bought this van knowing the engine needed work. My question is replace or rebuild? First, it's got 475,000 miles on it. (transmission replaced ~50k miles ago) It runs, but you can hear it knock pretty hard when you get into higher RPMs. I did compression tests on all cylinders. I checked when the engine was cold.. I know it's suppose to be warm, I just needed to find anything major. I noticed cylinder 6 and 4 had no compression.

1,2,3,5,7,8: ~130psi
4,6: ~10-15psi

I was thinking maybe stuck or bent valves? When the engine is started you can tell it's not firing on all 8, but all the plugs were clean; no oil or anything. The exhaust is clean, even when you get on it. Should I tear off the heads and see what I'm dealing with? Or is there further checks I should perform before this? Also, can you take the heads off when the engine is in the van? From what I see it looks like it should be possible. Let me know what you all think, thanks!


I should note this was a shuttle van(note the mileage), always had all regular maintenance done on time every time.

[B-300]

I would verify the 4 and 6 cylinder compression when warm... It sounds like at least a valve job.
I had similair low compression on a few cylinders some time ago and the exhaust valve seats were "sunk-in" past the induction hardening in the heads.

[alloro]

Since cylinders 4 & 6 are next to each other, I would suspect a blown head gasket between them.

[B-300]

Could be. It still requires head removal to be repaired, I don't know why I didn't thing of that... also the center cylinders on each head tend to run hotter due to the adjacent exhaust ports... between 4-6, also 3-5 on the opposite side.

[draker]

Alright I thought the 2 being next to each other might have some relation. Is there enough room to get in there and pull the heads with the engine in the van? Looks like it, but I just want to make sure.

Also, What about the knocking sound? Possible valve stuck open or bent? I have a pretty good feeling that there is a head gasket leak, but I was thinking at the rear of the engine cause I found a small bit of coolant puddled up. I will retest with the engine warm. I didn't warm it up cause I was out of gas as well. I'll try it again and see what I come up with. Also I haven't been able to listen for the knock sound with the engine cover off.

thanks for the quick response!

[alloro]

Yes you can pull the head with the engine still in the van.
For the knocking, we'd have a better idea if you can tell us whereabouts the sound is coming from on the engine. Is it louder when cold or hot, is it there when driving or just at idle?

[alloro]

I don't know why I didn't thing of that...

Is that a rhetorical question? :ebrow:

[draker]

There was virtually no change in compression checks with the engine warm. 2 and 8 show some variation more than 20psi. 4 and 6 still show ~15psi. I tried to listen for the knocking sound but I didn't hear it. I didn't have a change to drive it today, and the tags are expired.. so maybe tomorrow.

I am looking at pulling the heads soon, any tips would be greatly appreciated. If anyone knows of a guide to do the heads/valves that would help. Also, cheap source for gaskets and whatever might be needed. Let me know, Thanks!

[draker]

So I got the heads off and indeed found the head gasket blown between 4 and 6. I am in the works of pulling the engine, and will evaluate what will need to be replaced/rebuilt. Thanks for the help!