Who has twisted a cam gear off?
03-29-2007, 12:19 PM
#1
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Who has twisted a cam gear off?
Hehe, any one ever twist their cam gear off on a first gen? Im talking about the shaft itself is broken about .5" behind the gear. I have a nice set of bent pushrods that accompany it too!
What may have caused this? The PO said he was just cruising the highway, then CLUNK, engine dead. Is it worth repairing because the darn truck is nicer than my driver, except it has an auto. I will post pics when I get home.
What may have caused this? The PO said he was just cruising the highway, then CLUNK, engine dead. Is it worth repairing because the darn truck is nicer than my driver, except it has an auto. I will post pics when I get home.
03-29-2007, 02:23 PM
#3
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I had a cracked cam gear once.
My engine had been in a front end collision and the crankshaft gear spun on the crank when the timing cover jammed into it from the collision. The timing key on the crank gear is a 1/4 (okay, .237) soft steel dowel pin that half engages the gear. The engaged half of the pin sheared off.
I figure the cam and crank gears stopped dead when the timing cover jammed between them but the crankshaft kept turning another revolution or a little less. Ended up with 8 bent pushrods and 5 shattered lifters. The cylinders still had compression, so I concluded the valves didn't punch any holes in the pistons; replaced the lifters, push rods, crank gear, cam shaft gear, and repaired the No.1 main bearing saddle and ran it.
Total cost with a spare engine for a donor was $1500; new water pump, oil pan, oil pump, oil pickup tube to put the sump in front, new bearings.
I bought a new set of pistons just in case but haven't installed them yet.
My engine had been in a front end collision and the crankshaft gear spun on the crank when the timing cover jammed into it from the collision. The timing key on the crank gear is a 1/4 (okay, .237) soft steel dowel pin that half engages the gear. The engaged half of the pin sheared off.
I figure the cam and crank gears stopped dead when the timing cover jammed between them but the crankshaft kept turning another revolution or a little less. Ended up with 8 bent pushrods and 5 shattered lifters. The cylinders still had compression, so I concluded the valves didn't punch any holes in the pistons; replaced the lifters, push rods, crank gear, cam shaft gear, and repaired the No.1 main bearing saddle and ran it.
Total cost with a spare engine for a donor was $1500; new water pump, oil pan, oil pump, oil pickup tube to put the sump in front, new bearings.
I bought a new set of pistons just in case but haven't installed them yet.
03-29-2007, 04:33 PM
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Seems like alot of $ to fix an engine, rather than to replace, Whatever caused this sheering of the cam gear took an awful lot of force, where did it come from, and what else did it effect that didn't fail yet?
03-29-2007, 05:46 PM
#7
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I dont know what caused it. Seven of the pushrods are bent so...???? I was thinking about pulling out the cam if I can, putting in a used one, see what kind of shape the lifters are in...is there a way to check the compression to determine if there are bent valves? Id like to avoid pulling the head and all but...
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03-29-2007, 09:07 PM
#11
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Good chance for a PDR cam, if you ask me. If there are no damaged valves and pistons, put a new cam in there and rock on. Last I looked the PDR cam NEW (no core) was <$800, included lifters, etc. Look on ebay for pushrods. I think the 12valvers are all the same. There is a set from a 1stgen on there now.
Daniel
Daniel
03-29-2007, 09:47 PM
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Do a leak down test and see how back the leak down is and what the compression is. If that looks good put a new cam AND LIFTERS in it and run it. When we still had B's in our fleet vehicles I replaced them around 225K. If they didn't fail they soon would have. We had a few brake, but mostly the lobes failed from the high idle time.
If the thing was at cruise and not turning a lot of RPM, especially with an slushbox, it may not have killed the pistons. You may have some bent valves, the leak down should show that. I would certainly keep the engine. It would be a good core for a build up if it can't be fixed easily.
If the thing was at cruise and not turning a lot of RPM, especially with an slushbox, it may not have killed the pistons. You may have some bent valves, the leak down should show that. I would certainly keep the engine. It would be a good core for a build up if it can't be fixed easily.
03-29-2007, 09:59 PM
#13
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Maybe it is just how I am seeing the picture, but the broken portion of the cam looks corroded, except for part of the edge? You should be able to tell from the surfaces that are left how the cam broke -- eg: are there lines were you can see a crack that propogated through the shaft over time, or any areas that are corroded, indicating an existing crack for a period before the final portion broke -- or an area with a grain pattern that looks different from an another area that is stretched or "smushed"?
Harmonic vibration can break the front of the cam off, especially on high horsepower engines. There was a thread about this a couple years ago, and how the Diamond B 370hp marine engine has a beefed up cam where the gear attatches, with extra long bolts that extend back past the first journal or something. It has been a while, so I don't remember exactly. That said, I think that you are the first broken cam I have seen posted on here . . . Hopefully it was a flaw from the factory, and you can just put a new cam in and drive a million miles with no trouble!
Harmonic vibration can break the front of the cam off, especially on high horsepower engines. There was a thread about this a couple years ago, and how the Diamond B 370hp marine engine has a beefed up cam where the gear attatches, with extra long bolts that extend back past the first journal or something. It has been a while, so I don't remember exactly. That said, I think that you are the first broken cam I have seen posted on here . . . Hopefully it was a flaw from the factory, and you can just put a new cam in and drive a million miles with no trouble!
