So I pulled the engine in my explorer. It has 245k miles and It cracked the driver side cylinder head. That in combination with a plethora of oil leaks is why I decided to pull the whole thing out. That way it would be easier to replace all the gaskets and clean it up. After the tear down i decided that i would rebuild the whole thing. However after pricing all the replacement parts, rebuild kit, and machining i figured it would be cheaper to just buy a low mileage engine. So I found one that had a claimed 87k miles on it from a junk yard for $500. I replaced all the gaskets, cleaned and painted the engine. As soon as I started the engine though it had a horrible rod knock. So today I went out to video the engine running so i could show the junkyard guy and get a replacement engine. However I noticed that once the engine started warming up the knock started going away. And once the engine was hot it was not knocking at all. At first I thought I might be due to clearances tightening up once the engine was hot so I stopped the engine and let it cool completely. After starting it again and a test drive it still hasn't made any abnormal noises. The only thing I can think is that there was coagulated oil in a passage somewhere preventing oil flow and once the engine was hot enough the coagulated oil liquefied and flowed through to where ever. Has anyone else had this experience from a junk yard engine that may have been sitting for a while?

 

I have had this happen a few times. Started up a mid 80's chev van that sat for two or three years. It smoked REAL bad and was knocking like crazy. I let it idle like this for a few minutes and then slowly drove it around the block. By the time I got back, the smoke had pretty much cleared, and the noise was almost gone.

Long story short, I bought the van cheap for a family member and drove it home and it was perfectly quiet and never smoked after that.

Drove it on a 7 hour trip two days later and it was fine. Was in the family another three or four years without incident.

I think your prognosis is correct, see how it does over the next couple of cold startups and you might be fine. Maybe change the oil after a few good drives.

 

I would suggest you still talk with the yard you got the engine from. Let them know it had this noise the first time you started it and you're going to give it a day or two to see if it seems to be just due to sitting for awhile. That shows them that you're reasonable but also gives them a heads-up that the issue was present from the first time you fired it up rather than giving them a rebuttal that you drove it hard for a week, destroyed the engine, and now want them to replace it.

Is this the SOHC engine with the timing stuff in the front and rear or the OHV engine?

-Rod

 

JMO, but any SOHC 4.0 should have the cam chain tensioners replaced regardless of miles or years. Early ones are trouble, all are suspect.

 

This is the pushrod engine. And yea calling the junk yard was the first thing I did. And that's the reason for me starting it again to take a video. I just wanted to show them what the engine was doing when I would bring it back to them. Because I didn't want to bring the vehicle to them and let them do the swap. I mean I'm sure they are capable but I'm a stickler for details and can sleep much easier know that I went over each nut and bolt.
I got home from work this morning and figured that the engine had sat all night long and was sufficiently cool and if it was gonna knock it would do it then. But it started and ran smooth. I definitely will be keeping a close eye on it though.

 

Congrats on your accomplishment. That's quite a feat. There's quite a bit of terror involved the first 10 minutes after starting up a replacement engine - new noises, smoke, smells, etc.

I had a '95 4.0 Aerostar that got totaled and I kept it in my driveway until the insurance was settled. After sitting for a month or maybe more, there was a heavy sounding knock coming from the engine the first time I started it up after sitting. The knock went away after the engine got warm. I let it sit a few weeks more after that and the knock returned at startup and went away when warm. Since the frame was bent, I eventually scrapped it so I don't know if the knock was just a result of sitting with a long time between starts. Did you prime the engine before you started it up? When I replaced the engine in my Honda with a JDM motor, the place that sold me the motor told me to crank the engine with the spark plugs removed until the oil pressure light went out. Once that was done, I installed the plugs and fired it up and no issues with any knocking.

What year is your Explorer? Did you have to evacuate the A/C and remove some of the A/C system? I'm curious because the Ford shop manual says you have to do this but I didn't know if there was a way around it.

On my '91 Ranger, it was hard enough to get the upper intake off with the rigid lines being in the way, so I could understand having to remove A/C tubes and the compressor to get the engine out. I haven't looked closely enough at my '98 Explorer to see if engine removal could be accomplished without taking apart the A/C, but the manual says it's required.

 

Thats why I won't buy another junkyard engine so long as my old one is rebuildable. Rebuilding the engine produces a better than new motor (if done properly) and long lasting results.

 

Yea I would have preferred to overhaul the original engine however after buying a new cylinder head, rebuild kit and machining it would cost much more than the route that i took. It's a gamble I know, actually this was the first time I picked up a junk yard motor a put it in.

Mike, as for your questions.
I did prelude the engine, however I built a "prelude canister" and ran a line to the oil pressure fitting to push oil into the engine. Which leads me back to my theory that there had to be some coagulated oil in a passage that didn't budge until it was hot enough to liquefy again.
As for the AC lines, my explorer is a 1999 model and is equipped with rubber lines coming of the compressor. So I just un bolted then compressor and held it out of the way with a rubber strap. Thus allowing me to forgo having the refrigerant evacuated.

 

But I should add that now that the knocking is gone. This engine with 90k miles runs much quieter than the tired engine it replaced. So I am definitely happy with the results.

 

Thanks. That's what I did on my Honda and was hoping could be done on the Explorer. I don't plan on doing this kind of job soon, but if I pick up a project, I'll keep this in mind.