help with a 4.0 91 explorer

kearnsncsu

Active Member
Joined
Jan 14, 2008
Location
Thomasville
the vehicle has around 280,00 miles on it. not sure if the motor has ever been rebuilt. ive had it for the past 60,000 miles and drove the crap out of it. i have a knock that has got worse over time. it would come and go and could be fixed with a good run through of sea foam or the like of upper cylinder cleaner. today the knock got worse and at times sounded like it was suckin air passed one of the valves. when i got home there was a distinct knock coming from what sounded like the center of the engine. i was hoping that i had broken a valve spring, rocker arm or something else that could be repaired from the top end. i removed both valve covers to find that nothing was broke and everything looked ok. i proceeded to remove the fuel rail and intake. all push rods and lifters look ok. so my question is what do you guys think could be causing the problem? i know the 4.0 has hydraulic lifters. is there any way to tell if one of the lifters has collapsed and causing the knock? any advice would be greatly appreciated.
 
Hows the oil pressure when it's at full operating temp? Does it hold steady and go up with the rpm's or does it fluctuate while idling? I would've done a compression test before I tore everything down. It would've been able to pinpoint which cylinder has a problem if any as well as a if it had a sticking valve, dead lifter, bad valve guides or worn out rings. The next step is to check out the bottom end. Pull the pan and check the bearings. IMHO if it has 280k it's not worth sticking too much money into the drivetrain. You may be better off and it may be alot easier and cheaper to go with a used replacment engine. You can get a complete V6(TB to Pan, w/ all accessories) from Pull-A-Part for less than $170 w/ a 30 day warranty.
 
yeah checking the compression probably would have been a good route to go but i didnt think about that and i dont have a compression gauge. the oil pressure has pretty much always stayed the same. some times in the summer when it gets hot it would drop at low idle but build right back up when the engine is idled up. i ran the motor with the valve covers off the see that all the valves were opening and closing. but that doesnt mean that once it heats up and the knock starts that one of the valves arent sticking. i guess i really should have checked the compression first to check that. is there a good way to check for stciking valves now that i have it tore down?
 
talked to someone about this today. they said that i could have broken a timing chain tensioner and the knock is the chain hiting the case. anyone heard of this?
 
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