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View Full Version : "Jumped time" with timing chain. Really?



Electrajim
09-05-2009, 01:35 PM
I havn't opened alot of engines in my life. I've replaced the timing chain on a few Buick V6's because the nylon covered gears are known to crack up, and break off with high mileage. This wear can cause slack in the timing chain and mess up crank to cam timing, but not quite as much as a whole tooth off I assume. I've done timing chains on Buick 350's, and 455's too.

My question is, on a Buick engine or other timing CHAIN engine, has anyone actually verified that an engine has "jumped time" after running fine?
My guess is that it is alot more common on belt valve timing systems, but how often does it happen on chain systems, especially the Buick engine?

I know when you degree a cam it changes the relationship with the crank a few degrees and the engine will run fine. Will an engine even start or run with with a timing set one whole tooth off?

Old timers, (pun intended) what's the real story.

Thanks,
ElectraJim

SPCL_DLX
09-05-2009, 02:43 PM
I'm like you, I haven't opened up a lot of engines in my life, but I have heard that this does occur. I suppose like any other metal, heat causes it to expand and over time will cause the chain to stretch. Imagine the torque that is put out during starting, running, accelerating, etc. I found this post to be interesting timing (sorry, bad pun) as I am having trouble getting my Buick started and I have replaced every ignition component without luck. I'm thinking that my timing chain may have skipped. I'm hoping to not have to go that route but I may have no choice.

kenm455
09-05-2009, 03:20 PM
will run,but not fine.i've seen a few buick v6's run with it out a tooth.once had a Ford pickup/351w show up at the shop,barely running that had jumped 3 teeth.also had a sbc that ran fine to the store,but wouldn't start to go home.
ended up that the chain was so stretched that it fell off the crank gear.

BUICKRAT
09-05-2009, 07:17 PM
I have seen numerous engines jump time and still run. We even had one at my shop that jumped time and then jumped back, a couple times. (Ran like crap when brought in, I checked it out, shut it off and it backfired on shutdown. Started it up and it ran fine. Next time I shut it off it popped again, and on restart ran like crap.)It was a Buick 3.8, '86, I believe. They tend to jump on startup and shutdown. The shoe had broken off the tensioner and caused excess slack in the chain.

I had a '69 F100 w/a 390 that jumped time. I was able to get it home, but it was seriously lacking power and by the time I got home the exhaust manifolds were cherry red. I took it apart to find the cam gear had lost every bit of nylon and was as sharp as a Ninja throwing star, but the teeth were only 1/8 inch high.

Just had an '01? Dodge van w/a 360 that came in w/a lack of power. Had just come back from the body shop. Somehow, that engine jumped time. 60k on the motor, and the chain/gears weren't all that bad. Go figure

RG67BEAST
09-05-2009, 07:57 PM
My freind said he bought 340 mopar and it sounded like a prostocker. The guy he bought it from said it ran like a bear. I tore it down to find the cam was off a tooth and had 6 broken valve springs. But it did run and had pretty mean idle.
Ray

Billhillytim
09-05-2009, 11:11 PM
I just replaced my chain over the last two days due to a crappy running miss among other issues. It definitely solved the problem, got rid of plastic gears, and a whole lot of slack in the chain. My old Delta 88 quit as soon as I turned the key off and never started again due to a timing chain jumping, so I know it happens and really sucks when it does.

John Codman
09-05-2009, 11:23 PM
Over the years, I have replaced numerous timing chains/gears. Roughly 85% were small-block Chevys or GM V-6s. Older Pontiac V-8s also were famous for gear/chain problems. I have also replaced chains/gears on Oldsmobile V-8s. The common link is that most of the engines that I have encountered that have actually jumped time and were towed in were GM, sad to say. I am only mentioning engines that have actually jumped time here. The cause was invariably high mileage and a stretched factory "silent" chain. The nylon teeth on the cam gear would start to deteriorate and the cam would lose it's proper relationship to the crank. I have done chains on Mopars and Fords as well, but I can't remember either that actually jumped time.

collector
09-06-2009, 10:11 AM
Pontiac V8 used to be the worst, many of them would tear up a timing chain and gears as soon as 60,000 miles. Was very common back in the 70s. Oldsmobile V8s would wear out rocker arms and shafts but didn't have any timing chain issues. Buick V8s were hard on water pumps and starters and also rarely had timing chain issues. Chevrolet V8s were hard on camshaft and lifters and also rarely had timing chain issues. Just a little history lesson here from someone who was there!

rmstg2
09-06-2009, 12:22 PM
Pontiac V8 used to be the worst, many of them would tear up a timing chain and gears as soon as 60,000 miles. Was very common back in the 70s. Oldsmobile V8s would wear out rocker arms and shafts but didn't have any timing chain issues. Buick V8s were hard on water pumps and starters and also rarely had timing chain issues. Chevrolet V8s were hard on camshaft and lifters and also rarely had timing chain issues. Just a little history lesson here from someone who was there!

The nice thing about the Ponco's was, that they were probably one of the easiest to change out the timing gears and chains.

Bob H.

John Codman
09-06-2009, 02:26 PM
To Collector - Gotta disagree with you (a little). The Oldsmobile V8s did have their share of problems with rockers/pushrods, but chains/gears were an issue. I had to have my wife's 350-powered Olds wagon towed home for just that reason. As I said - most did not actually jump time, but the chains were loose and the nylon on the cam gear was badly deteriorated. I did a lot of them. As to Pontiac - you are correct. The gears and chains were a major problem, and they were easy to do.

collector
09-06-2009, 02:58 PM
To Collector - Gotta disagree with you (a little). The Oldsmobile V8s did have their share of problems with rockers/pushrods, but chains/gears were an issue. I had to have my wife's 350-powered Olds wagon towed home for just that reason. As I said - most did not actually jump time, but the chains were loose and the nylon on the cam gear was badly deteriorated. I did a lot of them. As to Pontiac - you are correct. The gears and chains were a major problem, and they were easy to do.

It is true that the GM cars all used the fiber-geared cam sprocket and the chains would loosen up after 100,000 miles and start to be an issue on all of these brands, but the Pontiacs had big-time problems with them EARLY and they would jump time prematurely. That was the point of my post. They all would wear out in these areas eventually, but Pontiac was early wearing out timing chains, Chevrolets were early in wearing out camshafts, Buicks with starters and water pumps, etc. Make sense now?

Rivman
09-06-2009, 05:11 PM
My high mileage 430 '68 Wildcat would jump a tooth on a regular basis - just pull the distributor, set her back in one knotch retarded and you were good to go. First time it happened, we towed it in, after that I bought an offset distributor wrench and could repair it right on the spot. Never did a proper repair - sold 'as -is' ! :TU:

BUICKRAT
09-06-2009, 07:51 PM
Just a basic fyi from a veteran mechanic, (on the line for 30 years), almost all v-8's of the late 60's till the early 90's had nylon teeth on the cam gear. They were all subject to wear, and alot sooner than most people think.

Lack of oil changes or cheap motor oil were the main cause of early failure.

Many years ago I had a customer who insited we change his chain/gears in his chevy pickup every 30k miles.

I drove his trucks before and after the swaps, and the difference was night and day, like having a fresh motor.

I have since tried this with other vehicles, and the difference in power and throttle response is huge. Even the smallest amount of chain stretch makes a big difference in power output.


Thanks, rivman, I'll know where to go to look for my next car...NOT:blast: :blast:

atticus427
09-07-2009, 08:26 AM
Drove an '85 S-10 for awhile with the 2.5 L 4 cylinder. This engine doesn't have a timing chain but the gears on the camshaft and crankshaft interdigitate directly. When we rebuilt the engine, we were unsure how to time it as this was our first foray into computerized vehicles. On old cars, this usually involves pulling off a vacuum hose but on computerized vehicles you have to short circuit the computer. Anyway, didn't know this at the time, the timing was way off, and it ran like crap. I worked on it for months trying to figure it out and eventually the timing gears just ate themselves up. When we opened it up, there were teeth everywhere but where they were supposed to be. Taking the time to jam a paper clip in the diagnostic connector port makes all the difference.

John Codman
09-07-2009, 08:38 AM
:laugh: Hi Mike, I am going to write down the word "interdigitate" and when I figure out what it means, I'll add it to my vocabulary. Perhaps at some point in the future I can ask some good-looking woman if she"d like to "interdigitate" with me. Thanks for the new word! :laugh:

71skylark3504v
09-07-2009, 09:31 AM
So once you put a double roller timing set on you should be good for life. Right? I hope so.:bla:

No Lift
09-08-2009, 12:44 PM
Way back I had a 69 Skylark with a 350 2bbl. One day while driving it pretty much just tried to die. Managed to limp it home barely running. Checked the usual stuff finally getting around to the timing. It was retarded what seemed like 20 degrees. I figure that the distributer slipped so I reset the timing to the factory spec. Well the car idled ok and actually drove reasonably well but wasn't quite right. If you punched it the carb sounded like a giant Q-Jet(whaaaa....) but you were going nowhere fast.

Figured something else was wrong. Took the timing cover off and found that the gear had jumped a tooth. The nylon(?) teeth had cracked up and exposed the aluminum gear underneath. Installed a new set and it all worked fine after that.

Looking at how many teeth are on a stock gear set will tell you how far the cam will retard one tooth off. It is different between the aftermarket and factory replacement gears so it is, I think, 16-20 retarded if it jumps one tooth, which is alot.

Only ran into one problem. Sometime after that the car wouldn't get the oil pressure up on startup. If you ran the car at a low idle for many minutes with a few taps of the throttle it would finally come up and be normal. I used it everyday for work so I didn't have time to look into it better. It was nerve racking every day waiting to see if a bearing would start to rattle. I finally got around to installing a 455 I had been planning on so then I got a look at the 350. When I took the oil pump apart I found a piece of the timing gear lodged in the relief cup never letting it seat up. Live and learn.

69GSCAL
04-22-2010, 07:58 PM
My high mileage 430 '68 Wildcat would jump a tooth on a regular basis - just pull the distributor, set her back in one knotch retarded and you were good to go. First time it happened, we towed it in, after that I bought an offset distributor wrench and could repair it right on the spot. Never did a proper repair - sold 'as -is' ! :TU:

Randy,

You sure that wasn't a 69 Stage 1? I swear this is what was done to my car at one point. I just got done pulling the distributor on the car, lining up TDC on #1 and putting the dist back in. No Go! Can't the car to run unless I set up the dist. with the rotor pointed one plug before #1 AND put in an enormous amount of advance.

I haven't been able to pull the timing cover yet, but I'm thinking the the chain has skipped a tooth (or more) and someone else did exactly as you id at one point to "get along".

We'll see over the weekend!

Bent Rod
04-22-2010, 09:17 PM
Over the years, I have replaced numerous timing chains/gears. Roughly 85% were small-block Chevys or GM V-6s. Older Pontiac V-8s also were famous for gear/chain problems. I have also replaced chains/gears on Oldsmobile V-8s. The common link is that most of the engines that I have encountered that have actually jumped time and were towed in were GM, sad to say. I am only mentioning engines that have actually jumped time here. The cause was invariably high mileage and a stretched factory "silent" chain. The nylon teeth on the cam gear would start to deteriorate and the cam would lose it's proper relationship to the crank. I have done chains on Mopars and Fords as well, but I can't remember either that actually jumped time.302 in a 70 torino I had in high school did it to me. 180,000 miles and a teenager behind the wheel. My only other experience with this issue was a 454 Cheby with the nylon gear.

gui_tarzan
04-23-2010, 09:41 AM
I only wrench on my own now but back in "the day" I worked at a GM dealership for a couple of years and the number of busted, oem nylon cam gears we replaced was phenomenal. It was rivaled only by the worn out 307 camshafts.

V8TV
04-23-2010, 10:03 AM
Many years ago when I lived in Chicago, I bought a '69 Riv in LA and drove it home cross-country. Ran great! The day after my return to Chicago, it was dead. Game over. Chain jumped! Lucky it happened close to home where I had a fresh 455 waiting to go..

Rivman
04-23-2010, 04:46 PM
I only wrench on my own now but back in "the day" I worked at a GM dealership for a couple of years and the number of busted, oem nylon cam gears we replaced was phenomenal. It was rivaled only by the worn out 307 camshafts.
Had me one of those too - an under powered, full size '77 Pontiac Parisienne Broughm, sounded just like a movie house pop-corn machine as it backfired through the carb at WOT. Ended up re&reing the cam/lifters and it ran like a brandy new car ! :TU:

Sorry - "It was a 'high mileage', hard driven '68 Cat Aubrey !" . . . keep us posted though ! :laugh: :TU:

John Codman
04-23-2010, 08:53 PM
I had a '79 Malibu wagon with a 267 V8 that rounded several lobes on it's cam. The fix was a small-block 400 with an Edelbrock performer plus cam, a roller timing chain with steel gears, and Crane valve springs. No more valvetrain problems. Ever.:grin: