1967 L79 Timing Chain / Gear issue

[David K.]

Ref: 1967 L79, I have owned the car since 1973. It has the original motor, timing chain & gears.

About 5 months ago while driving my 1967 L-79 a ticking noise developed in the motor. My 2 mile return drive home was without incident. I drove the car into my garage and opened the hood. With the car idling I determined the noise was coming from within the timing chain cover. At this point, though a ticking noise was present, the car was idling perfectly. I then turned the motor off.





However, having said the above I welcome opinions from the NCRS community if the 67 L79 is a non-interference motor or should I expect to have some valve damage.

Any input, suggestions and / or repair tips will be greatly appreciated.

Thank you

Dave Kreps ( 23277)

[Patrick H.]

Re: 1967 L79 Timing Chain / Gear issue

Non-interference.

Go ahead and replace that timing chain and gears.

[Paul D.]

Re: 1967 L79 Timing Chain / Gear issue

Expect to find cam gear with nylon teeth sheered off. They are now in your oil pan. I can tell you that many have been replaced on small block Chevys over the years without even giving a thought to what is in the oil pan. That said, as easy as the oil pan is to remove on a Corvette and considering how much easier it will be to get a good seal at the front of the pan, I would drop it and clean it out. Chip.

[Joe L.]

Re: 1967 L79 Timing Chain / Gear issue

Expect to find cam gear with nylon teeth sheered off. They are now in your oil pan. I can tell you that many have been replaced on small block Chevys over the years without even giving a thought to what is in the oil pan. That said, as easy as the oil pan is to remove on a Corvette and considering how much easier it will be to get a good seal at the front of the pan, I would drop it and clean it out. Chip.

Paul------


It's not possible to remove the timing cover on a 1967 small block without first removing the oil pan.

[David K.]

Re: 1967 L79 Timing Chain / Gear issue



Hi Chip.....when I was searching the archives I found lots of information regarding the plastic coated gear. Had I been more versed on the topic, I would have been pro-active and replaced these parts before they failed. In any event, I plan on dropping the oil pan and doing a thorough cleaning as you mention.....thank you.

[Domenic T.]

Re: 1967 L79 Timing Chain / Gear issue

Joe,
There is a trick to doing it! It was a common thing at the dealership. Not done correctly you will get a leak. We just loosened the pan bolts half way back and pulled the timing cover off (top first). Secret is not to mess up the pan gaskets up and to use the front pan seal over. Now all that was IF there was not a leak in the first place. You take can clip/ or grind the edges of the timing cover to make the installation easier. wedge the pan down in the front and use brake cleaner on the gaskets and front pan seal. Favorite sealer and then with 2 phillips screw drivers One on each side of the timing cover (installing it bottom first), pry the cover into the 2 line up pins and screw everything back down. Wipe the squished out sealer and your done.
Won't leak or be detected if done correctly. A novice? Was a common practice at the dealership. Choice is the short cut or doing it right!
Possible, all the time.

Dom

[Joe L.]

Re: 1967 L79 Timing Chain / Gear issue

Joe,
There is a trick to doing it! It was a common thing at the dealership. Not done correctly you will get a leak. We just loosened the pan bolts half way back and pulled the timing cover off (top first). Secret is not to mess up the pan gaskets up and to use the front pan seal over. Now all that was IF there was not a leak in the first place. You take can clip/ or grind the edges of the timing cover to make the installation easier. wedge the pan down in the front and use brake cleaner on the gaskets and front pan seal. Favorite sealer and then with 2 phillips screw drivers One on each side of the timing cover (installing it bottom first), pry the cover into the 2 line up pins and screw everything back down. Wipe the squished out sealer and your done.
Won't leak or be detected if done correctly. A novice? Was a common practice at the dealership. Choice is the short cut or doing it right!
Possible, all the time.

Dom

Dom------


Are you talking about pre-75 small blocks or post-75? For 1975 GM revised the front oil pan gasket and front oil pan radius. I believe the purpose of this was to make "theoretically" possible the removal of the timing cover without pan removal.

Personally, I would not even attempt to remove the timing cover without oil pan removal for either pre or post 75. Way too much of a chance of leakage afterward. If that happens, which is likely, one starts the whole job over again. It's not worth the chance. Plus, on a Corvette it's so easy to remove the oil pan.

[Domenic T.]

Re: 1967 L79 Timing Chain / Gear issue

Joe,
yes pre 75 because I left the dealership in 71. As I said, not for a novice. I did about 50 with 100% no leaks @ 2.50 per hour. Risky, yes, but possible. CLEAN was what it took. Then sealer applied on the pan gaskets with a thin piece of metal. Factory warrantee needed coded pan gaskets turned in, so we would save about 1/3 gaskets to turn in. Gaskets had no part # on them, but were coded with colored thread that the factory rep looked at when he approved the work.
Factory warrantee and customer pay. Trick is removing any oil on seals.
Maybe I should say "don't try this at home". The cars needed to have the engine lifted, dist removed and other things disconeccted to lift the engine and pull the pan. Then the crank turned 1/4 at a time to get the pan to clear the journals. Vette, no problem, cross member allowed the engine to stay mounted.
About every thing I do now is pre 75. No computers, cat converters, and I can see the spark plugs.

Dom

[Domenic T.]

Re: 1967 L79 Timing Chain / Gear issue

Joe,
I wasn't trying to be a smart a??. Just that we were replacing ALL the plastic cam gears before they bent valves. Was very common at about 75K and easy to find a loose chain or bad plastic.

Dom

[Joe L.]

Re: 1967 L79 Timing Chain / Gear issue

Joe,
I wasn't trying to be a smart a??. Just that we were replacing ALL the plastic cam gears before they bent valves. Was very common at about 75K and easy to find a loose chain or bad plastic.

Dom

Dom------

The strange thing is that GM started using the nylon toothed cam sprockets for small blocks in 1966 and never looked back. As far as I know, all PRODUCTION Gen I small blocks were equipped with nylon-toothed cam sprockets right through the end of the use of that engine in PRODUCTION. However, GM ceased SERVICING the nylon tooth sprocket about 1975 and replaced it for SERVICE only with a cast iron sprocket.

PRODUCTION passenger car big blocks always were equipped with a nylon toothed cam sprockets from 1965 through 1974, including L-88 and ZL-1.

[Richard G.]

Re: 1967 L79 Timing Chain / Gear issue

I have to believe the trick worked well and made the mechanic some money as they were not doubt working to beat the "flat rate".
However, I have serious doubts it would work on a gasket that is some 50 years old. I would pull the pan and install new gaskets.

[Gary P.]

Re: 1967 L79 Timing Chain / Gear issue

I'f it was me, I would pull the motor (4 hr) remove pan,fix problem, clean entire motor and detail everything,including engine compartment. reinstall.

[Guest]

Re: 1967 L79 Timing Chain / Gear issue

I would replace the timing chain and gear with update steel one's then do a simple compression test and see from there, if the reading look good then it your choice to remove the pan and clean out the plastic teeth out .

[Duke W.]

Re: 1967 L79 Timing Chain / Gear issue

I always thought the SHP engines were interference type. It would be a good idea to loosen all the rocker arms and verify that all the valves return to the fully closed position. If they do, none should be bent.

Cloyes manufactures both the OE replacement car silent chain - the later narrow version - and the truck roller chain. All have steel crank sprockets and cast iron cam sprockets. The latter should be more durable, but either will likely outlast most of us. Both are available with either one indexing hole or three to allow +/- four degrees cam reindexing, and all are about 30 bucks for the set.

They are sold in various brands/part numbers. You can find the NAPA part numbers at napaonline.com.

Duke

[Gene M.]

Re: 1967 L79 Timing Chain / Gear issue

I always thought the SHP engines were interference type. It would be a good idea to loosen all the rocker arms and verify that all the valves return to the fully closed position. If they do, none should be bent.

Cloyes manufactures both the OE replacement car silent chain - the later narrow version - and the truck roller chain. All have steel crank sprockets and cast iron cam sprockets. The latter should be more durable, but either will likely outlast most of us. Both are available with either one indexing hole or three to allow +/- four degrees cam reindexing, and all are about 30 bucks for the set.

They are sold in various brands/part numbers. You can find the NAPA part numbers at napaonline.com.

Duke

I think your right the dome pistons and higher lift cam seems like it could be interference when pistons are full up and intake valve full open. A lot of variables such as deck height of piston, head gasket thickness, rocker arm ratio, and increased lift if aftermarket camshaft.