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Joined: Jan 2009
Posts: 341 Likes: 3
Backyard Mechanic
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OP
Backyard Mechanic
Joined: Jan 2009
Posts: 341 Likes: 3 |
Hi All
Bob@marxparts here. I have a question concerning timing gear combinations in 25-28 Chevrolet 4 cylinder engines. From what I can see in the 1928 and 1940 issues of the 4 cylinder parts manuals, up to 1927 they used 5/8 inch wide gears and in 1928 they changed to 13/16 inch gears with a combination of either steel cam and fibre crank or fibre cam with steel crank gears.
I have a customer which is a machine shop rebabbitting the main bearings. To accurately line bore the main bearings once they are done, the machine shop uses the center line of the cam and the crankshaft with appropriate gear lash to line bore the engine main bearings. With the gears they have now it is way off.
The engine is a 1926 block with a casting number of 346709 with a date code of C 23 26. The camshaft casting number is 340590. Everything is 1926 from what I can tell. This engine now has a 13/16 wide fibre cam gear and a 13/16 wide fibre crankshaft timing gear in it (1928) which is not right. Also from what I can see in the parts manuals, the timing gear cover is the same 1925-28 part number 345511. If I get the correct timing gears (5/8 inch wide), will I have problems with something else? Is the front oil slinger different or something? Will the 28 wider gears replace the 27 and prior narrow gears and if so what needs to be changed? I know there is some one out there more familiar with this than I am who has the answer. I want to make sure that my customer gets the correct gears for this engine. Thanks much to whoever replies. Bob@marxparts
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Joined: Dec 2001
Posts: 10,379 Likes: 1
Technical Advisor ChatMaster - 10,000
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Technical Advisor ChatMaster - 10,000
Joined: Dec 2001
Posts: 10,379 Likes: 1 |
Early timing gears were 5/8 and fiber. The crank gear was 5/8 and steel. 1927 crankshaft gear is 13/16 fiber and is used with the 1927 camshaft gear which is 13/16 steel. 1928 used a 13/16 fiber cam gear and a 13/16 steel crank gear. Use caution with the 13/16 fiber timing gears in that some are are not marked correctly. Always check the Chapter on the timing/cam gears in the Repair Manual and count the teeth to be absolutely correct. Don't attempt to mix and match either gear. By all means do not attempt to shave a 13/16 gear down to a 5/8 gear. Once the coating on a fiber gear is penetrated, it is worthless.  
RAY Chevradioman http://www.vccacolumbiariverregion.org/1925 Superior K Roadster 1928 Convertible, Sport, Cabriolet 1933 Eagle, Coupe 1941 Master Deluxe 5-Passenger Coupe 1950 Styleline Deluxe 4-Door Sedan 1950 Styleline Deluxe Convertible 2002 Pontiac, Montana, Passenger Van 2014 Impala, 4-Door Sedan, White Diamond, LTZ 2017 Silverado, Double Cab, Z71, 4X4, White, Standard Bed, LTZ If you need a shoulder to cry on, pull off to the side of the road. Death is the number 1 killer in the world.
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Joined: Jan 2009
Posts: 341 Likes: 3
Backyard Mechanic
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OP
Backyard Mechanic
Joined: Jan 2009
Posts: 341 Likes: 3 |
Hi Antique Mechanic
Thanks for your reply to my question. The information that I was really after is if the 13/16 inch wide gears can be correctly used in the 1926 engine as this is what is in the engine now or if they should be switched back to the 5/8 gears like the parts books call for and what will change such as the oil slinger on the crank or something else that I am not aware of? Thanks Bob@marxparts
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Joined: Dec 2001
Posts: 10,379 Likes: 1
Technical Advisor ChatMaster - 10,000
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Technical Advisor ChatMaster - 10,000
Joined: Dec 2001
Posts: 10,379 Likes: 1 |
Don't know where you obtained the extra space under the timing cover to fit the 13/16 wide gear. Can't see any problem if both gears are 13/16 if you have the room to mount them under the cover.
RAY Chevradioman http://www.vccacolumbiariverregion.org/1925 Superior K Roadster 1928 Convertible, Sport, Cabriolet 1933 Eagle, Coupe 1941 Master Deluxe 5-Passenger Coupe 1950 Styleline Deluxe 4-Door Sedan 1950 Styleline Deluxe Convertible 2002 Pontiac, Montana, Passenger Van 2014 Impala, 4-Door Sedan, White Diamond, LTZ 2017 Silverado, Double Cab, Z71, 4X4, White, Standard Bed, LTZ If you need a shoulder to cry on, pull off to the side of the road. Death is the number 1 killer in the world.
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Joined: Nov 2001
Posts: 19,758 Likes: 64
ChatMaster - 15,000
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ChatMaster - 15,000
Joined: Nov 2001
Posts: 19,758 Likes: 64 |
Ray,
All you have to do is use the '28 cover.
How Sweet the roar of a Chevy four!
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Joined: Dec 2001
Posts: 10,379 Likes: 1
Technical Advisor ChatMaster - 10,000
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Technical Advisor ChatMaster - 10,000
Joined: Dec 2001
Posts: 10,379 Likes: 1 |
You are correct Chipper. I guess the decision is based on which timing gear you have a surplus.
RAY Chevradioman http://www.vccacolumbiariverregion.org/1925 Superior K Roadster 1928 Convertible, Sport, Cabriolet 1933 Eagle, Coupe 1941 Master Deluxe 5-Passenger Coupe 1950 Styleline Deluxe 4-Door Sedan 1950 Styleline Deluxe Convertible 2002 Pontiac, Montana, Passenger Van 2014 Impala, 4-Door Sedan, White Diamond, LTZ 2017 Silverado, Double Cab, Z71, 4X4, White, Standard Bed, LTZ If you need a shoulder to cry on, pull off to the side of the road. Death is the number 1 killer in the world.
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