Broken timing chain

Got a customers engine in Saturday that he thought had broken "sheared" a cam pin. Upon tear down I found the billet timing set chain was broken. This was a big pin and full with side bar chain, top of the line . Not only did it break the chain into, it pulled three or four side bars into around the chain before it pulled into.

It looks as maybe the cam bearings galled, being the oil pump shaft and gear are in good shape. It just surprised me it broke the chain and only having one pin and a 3/8th bolt.

It had a very thick washer under the bolt and big diameter. It goes to show the clamping force means a good bit, maybe more than the extra pin ore at least as much.

Good reason to do both along with a 7/16th bolt on a big roller.

So if it is a Coyles True Roller timing chain, then you can get a replacement Coyles chain only, without having to buy the gears or another full timing set. I don't remember the part number and right now I'm 800 miles away, however I can get it for you if you need it.


Charlie

"It looks as maybe the cam bearings galled"


The 1st thing to talk about.

Whose name is on the chain links? Does the cam spin free or is it seized? If it is a Cloyes just know they have street and race sets. They all are called true rollers. Even the billet one is available in street and race. Both have the 1/4" pins, but the street stuff has a chain a lot lower on the food chain which is why the street replacement chain is $15 and the race one is $65. P/N for the good chain is 9-134. Even then are a few different suppliers so hard to say if you get a good chain or very good chain.

I spoke with Cloyes at PRI and they are now offering the newer IWIS chain they call it the "Z-chain" I believe, its supposed to be 33% stronger than their previous best chain..... just food for thought

I think the number that Steve gave of 9-134 is the number for the replacement chain only, and is the number I'm trying to remember. The interesting thing is that the replacement chain for the big block Ford, is also the same number for the big block Chevy! Therefore the # 9-134 should be easy to find!

Charlie

How's the gear alignment?

Is it possible something broke off and fell in between the chain and gear? This would cause a break that might not be cam related.

just curious has any one read where Blake said he thought the Cam Bearings are ceasing? No matter how good a chain you have if there is a problem somewhere else something WILL break and it will be the weakest point....

Which came first , ...  chicken or the egg...?    I guess its possible that the bearings galled after it pulled material all the way around between the gear and the chain.....   Or it could have galled the bearings causing stress on the chain.....  

Talking with Cloyes , they had mentioned that they had some low tension engines (low rpm and spring pressure) breaking high end chains for some odd reason.... this is why they began to ressearch and offer a stronger chain, they attributed it to harmonics

I would tend to wander if the cam is larger than spec like many of the roller cams are, causing a lack of bearing clearance.....   Ive had to polish many cam bearing journals down to get enough clearnce......

JMHO

The cam is very easy to turn with the rockers on and adjusted, it just a 600 lift solid 150 lb seat 380 open nothing special. It just surprised me the chain broke when I have seen tons of the single pin 3/8 bolt deals shear.

This was pulled apart all looks perfect, you can even see where some of the plates were ob-longing the pin holes , sign of over loaded chain. I'm sure I will see a spun bearing when I get it down tonight.

This engine has been running too for a good while, just the stock D3 heads were pulled of and a set of ported Doves put on.

He said he thought the oil pressure had drop across the board about 10 lb.

One thing I would want to check is the condition of the pin in the distributor gear, in the event it locked up/kicked back for a second or two.

I will check the pin but I don't think that pin would break the chain if the oil pump locked up or dist shaft locked down.

I just wondered if it would stretch or bend as a possibility. I broke one in a stock duraspark driving up the return road. It just shut off with out skipping a beat....LOL

c.evans wrote:I think the number that Steve gave of 9-134 is the number for the replacement chain only, and is the number I'm trying to remember.  The interesting thing is that the replacement chain for the big block Ford, is also the same number for the big block Chevy!  Therefore the # 9-134 should be easy to find!

Charlie

Yes is the number you were trying to recall and is the "good" replacement chain. Yes is same as BBC and some Chrysler too! I'm thinking they must make the gears so that they can use the chain in a bunch of applications. They also offer this chain in a -5 and -10 which are for line bored engines that have the center to center .005" and .010" shorter respectively.

You can also get the better "z" chain mentioned P/N: 9-134Z.

#4 cam journal....just a guess.

IDT-572 wrote:I will check the pin but I don't think that pin would break the chain if the oil pump locked up or dist shaft locked down.

Usually it will break the teeth off the cam and/or distributor gear. If you are lucky it just shears the pin. Never heard of one snapping a chain. Been told the pin is just for locating and the interference fit supposed to keep things from slipping... sound familiar? 

Blake what set did you use? What name is on the chain links? I am thinking you either got a defective chain or it is a $15 chain. If it has black links and says ROLON you have your answer. Are some $100 billet sets that have some cheap chains and is easy to think you have something good and it is not. I have a nice Cloyes original roller here with the gold IWIS chain, but if I wanted a billet set I'd go with a Rollmaster GOLD as it always has a nice IWIS chain, built in torrington bearing and the gears are nitrited.

Its a no name set, in the engine when it came to me, but the chain looked like a good quality. I am going to the shop tonight and looking at the side bar.

jasonf wrote:Is it possible something broke off and fell in between the chain and gear? This would cause a break that might not be cam related.

I had this happen on a 351/400 years ago on startup. I put too much RTV and it got in a bolt hole in the face of the block, and part of the block around the bolt split and fell on top of the lower timing gear and broke a brand new Cloyes chain. I doubt it is possiable on a 429/460 though, by the design of the timing cover. Might want to check anyway?

The chain has SA stamped on one side and 06b on the other, side bars seem soft. I didn't get to pull the cam out, Parts came in for another engine and I started on it.