Failure New Jackshaft gear shattered, chain broken | Ford Explorer Forums - Serious Explorations

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Failure New Jackshaft gear shattered, chain broken

laker82

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March 28, 2015
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Year, Model & Trim Level
02 explorer xlt
Well I finally got back to installing the 4.0 liter in the 02 explorer. I had turned it over by hand through 4 cycles with no binding or problems. Fired on first crank and then nothing. Pulled valve covers and the right bank cam was not turning.
Pulled engine again.
Found a chain link had come off and the Al gear on the rear of the jackshaft was in 5 pieces, jackshaft is ruined.

Really not sure if link came off first or gear shattered first but I think it was the chain link as it is dented by a tooth.

Anyone else ever have a new chain fail? Or am I just special? The rest of the links on the chain look very lightly staked.

Was the original gear steel or AL?
 



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chains & sprockets

My 2000 Sport's original sprockets were not aluminum and the chains were very strong. Same was true for the OEM and Cloyes replacements. What company actually manufactured your replacement timing chain components? I'm surprised that an aluminum sprocket could damage the hardened steel jackshaft.
 






It was part of a kit supplied by the guy that did the heads. The guide is stamped Borg Warner not that means anything about the rest of the gear. Will see what I can find out about the kit.
The shaft was ruined by the chain after the gear broke and the bolt bent.
 






broken guide?

Is the cassette guide broken? If so, maybe the guide broke first and a piece got wedged against the chain causing a link to break. I have a set of Borg Warner cassettes in my storage room. I'll have to confirm that they don't have aluminum sprockets.
 






Most probable cause; I found a new way to fail. The jackshaft had about .008 gap between the shaft and collar before the oil pump drive when I removed it the 2nd time. If that was also true after the first failure there may have been a gap that carried up to the spacer between the oil gear and the timing gear. I do not know how flush the end of the spacer and the end of the shaft should be and I do not know where the bolt applies pressure between the gear and shaft/spacer. There may have been a strain because they were not flush. I should have a better idea when I have the new gear. It took a press to move the collar, but there may have been movement either the 1st or second time the gear locked up and the shaft spun.

The shaft new is $285 and used around 125 if I found one. It does not look like the spacer comes with the shaft. The shop who did the heads machined a new spacer that should work with the old shaft. I would like to know what others have found, is the end of the shaft and the end of the spacer perfectly flush or not ? ( where the gear face is torqued onto the jackshaft )

The gear was manufactured by SA Gear who denies there has ever been another failure. (or not our problem)
 






jackshaft thrust plate

I think the clearance in the rear is determined by the jackshaft thrust plate in the front.
JacshaftThrustPlate.jpg

I haven't been able to find the specified jackshaft to thrust plate clearance.
Edit: I found the camshaft end play for the OHV V6 which should be the same as the jackshaft end play for the SOHC V6: 0.0025 to 0.0064 inch

Its important that the oil pump drive retainer is in place and tightened correctly or there will excess clearance between the spiral gear on the oil pump drive and the spiral gear on the jackshaft.
OilpumpDriveRetainer.jpg
 






Thank you for feedback 2000StreetRod.
On the pump drive end there is a collar, then pump gear,then a spacer, then the bolt holds on the lower gear which lands on the shaft and the spacer. After the failure there was a gap between the 1st collar and the shaft. It looks like that gap moved the spacer away from the end of the shaft leaving a step on the shaft/spacer face where the gear fits on the end of the shaft. That could have put a stress on the gear that it is not designed for. That is the current theory anyway.
 






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