'66 vs '67 Federal Mogul Timing Set Difference??

[Bob S.]

Hi Folks - I'm collecting part numbers for a '66 L-79 rebuild. I'm also collecting the same info for a '67 L-79 since that rebuild will follow shortly after the '66.

Oddly, I find different p/n's on the F-M website for the two years: KT3-489S (w/223-261 cam sprocket) for '66 and KT3-499S (w/0.405" tooth width 223-390 cam sprocket ) for '67. Since a 223-390N nylon toothed sprocket is listed separately for '67, it appears the difference between the "sets" is NOT the nylon teeth....

Can anyone explain the difference? ....is there a difference in tooth width? .....or single vs double row?

TIA

Bob.....

[Joe L.]

Re: '66 vs '67 Federal Mogul Cam Timing Set Difference??

Hi Folks - I'm collecting part numbers for a '66 L-79 rebuild. I'm also collecting the same info for a '67 L-79 since that rebuild will follow shortly after the '66.

Oddly, I find different p/n's on the F-M website for the two years: KT3-489S (w/223-261 cam sprocket) for '66 and KT3-499S (w/0.405" tooth width 223-390 cam sprocket ) for '67. Since a 223-390N nylon toothed sprocket is listed separately for '67, it appears the difference between the "sets" is NOT the nylon teeth....

Can anyone explain the difference? ....is there a difference in tooth width? .....or single vs double row?

TIA

Bob.....

Bob-----


You've discovered a little bit of small block history that very few folks are aware of.

1955-66 small blocks, Corvette and otherwise, used cam and crank sprockets with teeth 0.56" wide (at the base). 1967+ small blocks used cam and crank sprockets with teeth 0.41" wide (at the base). In addition, the timing chains, which are of the "early link"/Morse style, are commensurately wider for 55-66 than for 67+. Single versus double row does not apply to "early link"/Morse style timing chains. That applies to ROLLER chains only and roller chains were never used on any PRODUCTION passenger car, including Corvette, small block.

1955-65 small blocks used a cast iron cam timing sprocket of the "wide" type. 1966 ONLY used an aluminum/nylon timing sprocket of the "wide" type, the ONLY use of a "wide" type timing set with aluminum/nylon cam sprocket on a small block. 1967 and later small blocks used the "narrow" type timing set, ALL with aluminum/nylon gear through, at least, 1975 and, likely, later for all Gen I PRODUCTION small blocks. The change which occurred in 1967 applied to ALL small block engines. Prior to 1967, the "wide" type was used for all Gen I small blocks REGARDLESS of engine RPO; for 1967 and later the "narrow" type was used for all Gen I small blocks regardless of engine RPO.

The timing sets can be interchanged between 55-66 and 67+ but ONLY AS A COMPLETE TIMING SET (i.e. both sprockets + chain). The 1967+ crank timing sprocket is designed with a "collar" so that the width of the sprocket is the same as 55-66. This ensures that harmonic balancer installed depth will be the same regardless of which timing set is used.

Pictured below are the "narrow" and "wide" timing sprockets showing the difference in width of the teeth, photos of a 1967+ GM #3902422 "narrow" crank sprocket showing both teeth width as well as the "collar" which standardizes the overall width of the sprocket with the 55-66 sprocket, and a photo of the 1966-ONLY GM #3865964 cam timing sprocket.

[Clem Z.]

Re: '66 vs '67 Federal Mogul Timing Set Difference??

if for any reason you decide to use a double row roller chain check for interference between the chain and the block behind the the cam gear.

[Bob S.]

Re: '66 vs '67 Federal Mogul Timing Set Difference??

Joe / Clem - You guys never fail to amaze me.....the dept of knowledge on this board is second to none!

I conclude it really doesn't matter which 'set' is used for my rebuilds. I'll probably go with the slightly wider (non-nylon) tooth configuration for both engines in the interest of slightly lower contact stresses....

Clem, researching timing sets on this site lead me to decide against a double roller configuration to avoid any possible chance of fitment problems.

Thanks again for the valuable insight.

Regards,
Bob S.

[Joe L.]

Re: '66 vs '67 Federal Mogul Timing Set Difference??

Joe / Clem - You guys never fail to amaze me.....the dept of knowledge on this board is second to none!

I conclude it really doesn't matter which 'set' is used for my rebuilds. I'll probably go with the slightly wider (non-nylon) tooth configuration for both engines in the interest of slightly lower contact stresses....

Clem, researching timing sets on this site lead me to decide against a double roller configuration to avoid any possible chance of fitment problems.

Thanks again for the valuable insight.

Regards,
Bob S.

Bob-----

You can use the cast iron timing gear instead of the nylon. In fact, you will have a very hard time obtaining the nylon-toothed cam sprocket. They are long-since GM-discontinued and even the aftermarket nylon-toothed cam sprockets are hard to find, if you can get them, at all. The cast iron is more durable than the nylon, anyway, just slightly noisier.

There can be interference as clem describes with the double roller sets. However, I've never had any problems, at least so far. If there is interference, it can usually be solved with very little grinding on the block. The Cloyes 9-3100 double roller set is my favorite for a small block above all others.

[Duke W.]

Re: '66 vs '67 Federal Mogul Timing Set Difference??

I conclude it really doesn't matter which 'set' is used for my rebuilds. I'll probably go with the slightly wider (non-nylon) tooth configuration for both engines in the interest of slightly lower contact stresses....

Regards,
Bob S.

I recommend the early (wide) timing set for all rebuilds. Apparently GM found that the later, narrower set has adequate longevity - I have a neighbor with a '77 Corvette, engine never touched, and it shows no signs of a loose timing chain at about 160K miles.

Nevertheless, the wider set may offer better longevity.

A primary cause of timing chain wear is dirty oil, so if you follow an oil chance schedule suitable to your driving habits (once a year or every 5K miles, whichever occurs first and use C-category oil), either set should last the life of the engine.

Also, assuming you can even find such, avoid a nylon tooth timing set like the plague!

Lastly, IMO these inexpensive Sealed Powed OE replacement sets are more than adequate for all engine restorations, and the more expensive aftermarket "roller chain" sets offer no real advantage for the increased cost.

Duke