1967 L79 Timing Chain / Gear issue

[Joe L.]

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

Duke------


OE crank sprocket for 1967+ small block chains was always powder metal, not steel.

[Mark E.]

Re: 1967 L79 Timing Chain / Gear issue

I always thought the SHP engines were interference type.

Duke

That's right. Some SBCs are interference; most are not. The question is which ones? I searched awhile ago, but never found a definitive list.
I believe (not 100% sure) all OEM hydraulic cam engines (including the L79) are non-interference, and some (not all) mechanical cam engines are interference.

[Patrick H.]

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 .

I'd remove the pan.

This is what I found in a 72:

[Dick W.]

Re: 1967 L79 Timing Chain / Gear issue

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.

I have removed the t/c without removing the oil pan quite a few times without any leaks. As Dom said, be patient and move slowly.

[Gene M.]

Re: 1967 L79 Timing Chain / Gear issue

Duke------


OE crank sprocket for 1967+ small block chains was always powder metal, not steel.

Both of you are right. I suggest the material is derived from a steel or iron of some nature.

Here are just a few of the material options for powder metal parts.

Workpiece material Density (grams/cc) Yield strength (psi) Tensile strength (psi) Hardness (Units?)
Iron 5.2 to 7.0 5.1*103 to 2.3*104 7.3*103 to 2.9*104 40 to 70
Low alloy steel 6.3 to 7.4 1.5*104 to 2.9*104 2.00*104 to 4.4*104 60 to 100
Alloyed steel 6.8 to 7.4 2.6*104 to 8.4*104 2.9*104 to 9.4*104 60 and up
Stainless steel 6.3 to 7.6 3.6*104 to 7.3*104 4.4*104 to 8.7*104 60 and up
Bronze 5.5 to 7.5 1.1*104 to 2.9*104 1.5*104 to 4.4*104 50 to 70
Brass 7.0 to 7.9 1.1*104 to 2.9*104 1.6*104 to 3.5*104 60

[Philip A.]

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

You may be correct regarding the SHP motors. If you look carefully at 1965 engine listings the L79, which is hydraulic lift, is an HP motor, while the L76, FI, and BB, which are all solid lift, are listed as SHP.
Phil

[Duke W.]

Re: 1967 L79 Timing Chain / Gear issue

Both L-79 and L-76 are SHP. For example, in the P & A catalog the '65 L-79 camshaft is listed as "Sp. H/Per. w/Hyd.lifters" and the L-76 cam as "Sp. H/Per. w/Mech. lifters".

I believe when the 250 and 300 HP 327s coexisted the 300 HP engine was referred to as Hi. Per.

The L-36/68 camshafts are referenced as "427 exc. Sp. H/per, H.D."; L-72/71 as "427 w/Sp. H/Per." and the L-88 cams as "427 w /H.D."

Too bad they didn't list by horsepower ratings as the HP, SHP, and HD terminology can be confusing.

Duke