timing gear pin killed another good engine!

Right now...repairing a "big boy" 638 C head mill...belt drive..that sheared both pins.
I suspect it may have been run loose. It wiped out the cam drive hub.
Ugly failure.
Keith

anyone ever thought to tap the pin holes and use grade 8 bolts instead of pins.

I am not sure that would gain anything, plus there would be clearance issues at front of the gear. More machine work, compatability issues and accuracy issues.
Two pins are fine as long as good assembly methods and components are used.
Keith

4 Pins!

Wheelie58 wrote:I am not sure that would gain anything, plus there would be clearance issues at front of the gear. More machine work, compatability issues and accuracy issues.
Two pins are fine as long as good assembly methods and components are used.
Keith

what is gained is the bolts replacing the pins would be in tension so that the loading on the side would be always be a shear force instead of a bending one. Pins do not tolerate bending well.

466cj wrote:

Wheelie58 wrote:I am not sure that would gain anything, plus there would be clearance issues at front of the gear. More machine work, compatability issues and accuracy issues.
Two pins are fine as long as good assembly methods and components are used.
Keith

what is gained is the bolts replacing the pins would be in tension so that the loading on the side would be always be a shear force instead of a bending one. Pins do not tolerate bending well.

Good point...
If the gear or belt drive hub is tight and happy (with the center bolt) the pins are always in shear mode and are fine. I understand what you mean, with using bolts.
Not meaning to question your intent, just giving my 2 cents on the topic. Your point is very valid.
Thanks,
Keith

Wheelie58 wrote:Right now...repairing a "big boy" 638 C head mill...belt drive..that sheared both pins.
I suspect it may have been run loose. It wiped out the cam drive hub.
Ugly failure.
Keith

Like Kieth said, loose will kill one or two pins. If the cam gear can wobble things get bad in a hurry. When installing a 2nd pin using a Danny Bee 4340 chromemoly unit is an advantage i.m.o.

Would a gear drive be any tighter than a belt drive?

Wheelie58 wrote:

466cj wrote:

Wheelie58 wrote:I am not sure that would gain anything, plus there would be clearance issues at front of the gear. More machine work, compatability issues and accuracy issues.
Two pins are fine as long as good assembly methods and components are used.
Keith

what is gained is the bolts replacing the pins would be in tension so that the loading on the side would be always be a shear force instead of a bending one. Pins do not tolerate bending well.

Good point...
If the gear or belt drive hub is tight and happy (with the center bolt) the pins are always in shear mode and are fine. I understand what you mean, with using bolts.
Not meaning to question your intent, just giving my 2 cents on the topic. Your point is very valid.
Thanks,
Keith

Hi Keith,

Thanks you for the reply. I DO get what you are saying, just wondering if anyone ever did what I was thinking of. My thought was if the cam has a 3/8" bolt may be an alternate way to go than machining the center for a 7/16" bolt. I have a double pinned roller cam here with a 3/8" bolt so may give it a try.

Steve

is the block filled ?

Steve,
I have more than one double pinned 3/8" bolt BBF roller engine out there running successfully.
There is another good option. Engine Systems has a woodruff key option for the BBF.
We broach the gear and cut a matching keyway in the cam nose.
It has been thier standard race prep for years.
Call me if you want details,
678-458-2033
Keith

I havent had too many pin problems ,but the two times I have its been a filled block with std. style cam bearings,going to roller cam bearings fixed it.