Dump the gear and go timing chain?

[Alky V6]

The flat roller ider gear is no longer available. You can only get the roller ball bearing style idler that uses the single large bolt through the middle. The replacement is a SBC part.
My mounting plate uses two bolts other than the two behind the cam gear. For the bolts at the bottom of the plate, the one nearer the idler gear is 1/4-20, and the other one is 5/16-18 x 3/4 and is located opposite side of the plate of where the idler gear is. They are both allen socket head cap screws. They both thread into the block.
I don't remember the sizes behind the cam gear. Those are both button head cap screws. If I recall correctly, the size of the button heads behind the cam gear are larger than 5/16". I can check for you when I get to the shop.

 

[Alky V6]

I recalled correctly. The button heads behind the cam gear are 3/8-24 x 3/4". They thread into special allen plugs that are threaded into the front ends of the oil galleys. These special allen plugs have the IDs drilled out and tapped to accept the 3/8 button head cap screws.

Torque specs are;
Large idler gear axle bolt - 85 ft/lbs
3/8-24 x 3/4 button head cap screws - 25 ft/lbs
5/16-18 x 3/4 socket head cap screw - 20 ft/lbs
1/4-20 x ? socket head cap screw - 12 ft/lbs
Use Loctite on all cleaned threads.

 

[Alky V6]

The hardware I just listed may be different than what came originally with the gearset kit. According to the installation instructions, the 5/16-18 allen bolt should have been a button head cap screw. I may have swapped it out because I like the socket head better.

 

[Mike E]

I think your TA block uses different oil galley plugs from an iron stage block. TA looks to have o-ring fittings. The stage block uses 3/8" npt plugs that have a 5/16" hex. That only allows me to drill and tap them to 5/16-18. If you have the cam gear removed, I sure would like to see how the plate it counterbored for the bigger bhcs.

For the lower holes since they are already tapped into the block, I can't use the specified milodon precedure for locating them. I'm going to make a stepped washer that is roughly 3/4" od on the big end of the step and 1/2" on the small end, with the small end just shy in length of whatever the plate thickness is. I'll punch the existing holes in the plate out to 9/16"-5/8". Then when I get everything assembled and the backlash set, I'll weld the stepped washers to the plate to positively locate the plate with the propper backlash. If my mill had the head room, I would just add a couple dowel pins and be done, but I need a riser.

 

[Alky V6]

I just checked some old hardware that came off of a spare Stage II iron block I have that ran a geardrive, old circle engine, and the hardware that came off of my old v2.0 Stage II on-center iron block (RIP). They are both using the same allen pipe plugs in the block that my gearset came with originally.
The pipe plug is a 3/8 npt, drilled through the middle and tapped to accept 3/8-24 threaded bolt. The instructions say the bolts are 3/8-16, but the threads in the pipe plugs are 3/8-24. A 5/16-18 tap falls right through the hole. I checked. It is not 5/16. The tapped hole in the pipe plug is so large that barely any of the hex is left of the allen plug to use a wrench on to install the plugs.
You're correct about the TA block. They come with o-ring sealed, straight thread plugs. I tapped the holes in the block to accept brass pipe plugs, and then drilled and tapped the installed pipe plugs for the 3/8 hardware to mount the plate. You've got to have some faith to use the geardrive on a TA block.

 

[Alky V6]

I don't remember what size pipe plugs I had to go with on the TA block. I may have had to tap the block for 1/2 npt brass pipe plugs, then install the pipe plugs, face them off, then drill and tap them to accept the special 3/8 npt pipe plugs that come with the gearset. Yep. That's what I did.

 

[norbs]

Jay had some bad experiences with gear drives, so I am nervous about them.

 

[Alky V6]

Jay had some bad experiences with gear drives, so I am nervous about them.

I think Jay stated that he found the gear in the pan with all bolts intact. That tells me that someone didn't tighten the bolts properly, or Loctite wasn't used, or both. That is simply an assembly error. If one is that scared, they can lock wire the bolts.
I've had the chance to check on the particular gearset I'm now using in my TA block about 4 times in two different engine builds throughout the years. Everytime, the bolts were holding very well with only red Loctite. If you don't trust your own assembly techniques, then don't use a geardrive, and deal with the troublesome chain drives.

 

[Mike E]

Since I'm using a stage 2 front cover, I'm thinking about adding a preload bolt on the front cover. That would keep the idler gear loaded against the mounting plate and maybe it will add some support. The really high quality RCD gear drives that blown pro mods and fuel cars use have the gear secured from both sides instead of cantilevered like the buick milodon drive.

 

[Alky V6]

Since I'm using a stage 2 front cover, I'm thinking about adding a preload bolt on the front cover. That would keep the idler gear loaded against the mounting plate and maybe it will add some support. The really high quality RCD gear drives that blown pro mods and fuel cars use have the gear secured from both sides instead of cantilevered like the buick milodon drive.

I think that if the idler gear was straight inline with the crank and cam gear, the idler bearing and shaft would be seeing quite a bit of load. But, with the idler gear set off to the side like it is and the other gears meshing with it where they are, I'm going to guess the idler bearing and shaft don't see as much load as you'd think. I'm just guessing. I'm not a mechanical engineer so maybe someone can correct me.

 

[Alky V6]

I visualize two forces acting on the idler gear as the crank gear is applying torque to it and the idler applying torque to the cam gear. One force is attempting to suck the gear in between the crank and cam gear, and the other is attempting to spit the idler gear out away from the other gears. I just don't know if the two forces are perfectly offsetting each other.
If the forces are perfectly offsetting each other, then the idler bearing and shaft are seeing very little loading.
If the forces are not perfectly offsetting each other, then I think the loading on the idler bearing and shaft is still less than it would be if the idler gear were inline with the crank and cam gear and being driven by the crank gear.

 

[Mike E]

There is also the force from the pressure angle on the teeth trying to force the gears away from each other. Thats the one that is the problem with the idler set to the side of both gears. If the idler was centered between the cam and crank the pressure angle forces would cancel each other.

 

[Alky V6]

The force trying to spit the idler gear away from the other gears has to do with the angularity of the contact points between both crank/idler and idler/cam gear pairings.

 

[Alky V6]

There is also the force from the pressure angle on the teeth trying to force the gears away from each other. Thats the one that is the problem with the idler set to the side of both gears. If the idler was centered between the cam and crank the pressure angle forces would cancel each other.

The post previous to this one I was creating before I saw this quoted post. You are right, Mike, about the pressure angle. That is what I was referring to above that is attempting to spit the idler gear out away from the other gears.
If the idler were centered between the other gears, the driving force of the crank gear would attempt to push the idler gear to the right side. The force of the idler driving the cam gear would again be attempting to push the idler gear to the right. The forces would not be cancelling each other. They would be adding to each other to try to spit the idler out to the right side.
But, you are right that the forces brought about by the angularity of the teeth in contact would be cancelling each other out. The crank would be trying to spit the idler upward, and the cam gear would be trying to spit the idler downward.
Two forces in play here. The torque of one gear trying to move another, and the force brought about by the anglularity of the contact points of the teeth of the gears.

 

[Alky V6]

I think we're talking about the two forces of each gear pairing, creating a single force vector at each pairing. And, as the idler gear position changes from inline with the other gears to out to the side, so does the projection points of the force vectors of each gear pairing.

 

[Alky V6]

As the idler gear is moved more out to the side, the projections of the force vectors of each gear pairing attempt to point at each other. The closer they get to pointing at each other, the more the vector forces are attempting to cancel each other out.

 

[Mike E]

This was wrong and misleading. See two a few posts later.

 

[Mike E]

The neat thing about the gear drive is that those component forces Fr and Fc have a reaction on the crank and cam gears. Forcing the crank down into the cap and forcing the cam up into the lifters. The drivers side bank of lifters create a force in the opposite direction canceling some if not all of that force Fc.

A timing chain does almost the opposite.. The timing chain pulls the gear down towards the crank and combined with forces from the lifters puts a lot of stress on the oil film on the cam bearing.

 

[Alky V6]

I don't quite agree with the direction of some of your forces.

 

[norbs]

I think the 2 forces cancel each other in the gear drive so the net force is zero becausse the direction of rotation is reversed , or am I a failing student ?