Gear drive harmonics

[George]

I ran a 355 stack injected SBC for several years with a double roller chain timing set. Last year we decided to go with a blown combination and I stayed with the chain. After an additional 30 runs we took the engine apart and found the chain had stretched a good deal so I bought a Donovan gear drive. The gear drive is a well built piece but we are having an issue with bolts vibrating loose on the timing cover. I feel certain we have a harmonic associated with the gear drive . I am going to take it apart soon but other than studs and red locktite what should I do or look for? I do run a standard dia. crank snout with a outboard bearing support. Even if I can keep the cover from coming loose , I'm concerned about crank and bearing longevity.   Thank you . George

[Paul New]

Sounds like the mesh of the gears is a little tight not enough backlash

[msundstrom]

Detonation will loosen bolts also.
Mark

[FEDNV]

I run a Milodon gear drive on my BBC and have never had any of those issues.  My guess would be to go back over the install process and make sure everything is adjusted and installed perfectly.

[BK]

A friend had similar issues. Turned out to be a cracked crankshaft. Not saying that's you problem. I would think it could create some harmonics though.

[George]

No problems until the gear drive was installed. A call to Dononvan tomorrow might help us get squared away on the backlash. It's not in their installation information.

[dreracecar]

Donovan are fixed gear and the backlash is what it is, no adjustment.

[Paul New]

you can adjust the backlash I remember doing this years ago. I just did a little Google action and found some Milodon gear drive instructions.
http://www.milodon.com/instructions/gear-drive-13600-thru-14600.pdf

[George]

you can adjust the backlash I remember doing this years ago. I just did a little Google action and found some Milodon gear drive instructions.
http://www.milodon.com/instructions/gear-drive-13600-thru-14600.pdf

Thanks Paul. Appreciate the help. George

[dreracecar]

Paul-- its not a Milodon, it is a Donovan and the idler is fixed (thats what needs to be moved to adjust backlash) the cam gear is fixed and the crank gear is fixed so there is no adjustment one can do unless they move the timing cover itself or make +1 or -1 cam/crank gears.

Friends with everybody over at Donovans and worked there awhile ago, never a fan of their geardrives unless it was for a 392/417. always ran a Summers geardrive on my Chevy because it was a little more user friendly and every sprintcar in the country uses them.

[Draw 3D]

The Milodon is solid also, the adjustment is made by the complete unit thru the mounting bolts to the block.

[Paul New]

Paul-- its not a Milodon, it is a Donovan and the idler is fixed (thats what needs to be moved to adjust backlash) the cam gear is fixed and the crank gear is fixed so there is no adjustment one can do unless they move the timing cover itself or make +1 or -1 cam/crank gears.

Friends with everybody over at Donovans and worked there awhile ago, never a fan of their geardrives unless it was for a 392/417. always ran a Summers geardrive on my Chevy because it was a little more user friendly and every sprintcar in the country uses them.

Yes I know it was a Donovan unit but I have run both and have adjusted the backlash the same way on both gear drives.

[dreracecar]

Donovan is not going to sell this that requires machine work to install. most people dont have the capability to re-machine the dowel pins at the front of the block, besides checking the idler at both crank and cam. Thats why I chose the Summers unit that used a seperate cover, Backlash was set by loosening the idler carrage and rolling a folded piece of paper at the crank and cam and tighten the 3 bolts of the carrage. Install cover locating on the 2 dowels and your done and everything lines up.

The backlash is pre-set for a un-altered block, If it has been damaged and re-line bored so that the crank has been raised you will have problems, thats where the summers unit comes into play

[Paul New]

Understand that Bruce I do have a complete machine shop and forget not everyone has this option

[George]

Doug and I will dig into the Donovan gear drive tomorrow. Doug is the driver and a mostly retired machinist. He and I went to the same trade/high school in the early 70s. I'm the semi-retired electrician/ machinist's helper. I printed the Milodon installation instructions for the SBC and it looks like a good Doug project. We can't leave it like it is . It will shake it self apart. Thanks guys. George