With separate units the frame has to be designed to be rigid between the two points. Take a look at one of the older harleys like a rigid and you will see what's missing. Probably that vertical tube that was used to mount the rear of the engine. Without seeing the frame and install, I'd honestly just be guessing on the best approach. I will say in order to snap the bolts there is a lot of movement in the engine / trans combo for it to happen.
Ron

 

Definitely check the mounts because something is allowing too much movement/stress. Can you post any pics with a digital camera?

 

I'm going to try to get to the garage this weekend, I'll bring my camara with me post them up.

 

nosinjcted,
Engines mounts and transmissions mounts need to be shimmed to ensure proper alignment of those components. If they are not properly shimmed it can cause excessive stress on the primary-to-engine bolt heads as well as twisting/cracking the primary housing.

 

Do you have a link to the proper procedure to ship the engine and transmission?

 

I was taught to align the engine/trans as follows:
This procedure hinges on the primary being machined properly and not twisted. It can be checked for twist with a level on it's machined surfaces for the trans and engine.
There must not be any paint on the mount surfaces and even chrome plating on mount surfaces can adversely affect this but you're kinda stuck with what ya got if anything has plating on it.
Loosen engine mount bolts including the upper mount. Loosen primary-to-engine and transmission bolts/nuts. Loosen the four transmission plate-to-frame bolts and/or nuts and the fifth bolt under the right side of the tranny (you could do this on the four tranny-to-plate studs but I think they are harder to get to when installing the shims and you still have to do the fifth bolt under the right side of the tranny).
Tighten the primary to engine and trans bolts/nuts. This gets the engine/tranny aligned to one another. Loosen the bolts and/or nuts you just tightened.
Tighten the rear engine mounts. Check, with a feeler gauge, the front engine mounts for any clearance. Make whatever size shim needed for the front engine mount "ears" and tighten up the front engine mounts.
Tighten the primary to engine then primary to transmission bolts/nuts.
Check, with a feeler gauge, the tranny plate to frame mounts. Shim as necessary and tighten them up.
Check, with a feeler gauge, the fifth tranny to frame mount under the right side of the transmission. Shim as necessary and tignten it up.
Adjust or shim as necessary, the upper engine mount and tighten it up.
Anything that requires a shim of less than .005" I don't bother to shim. but if it bugs ya get the shim stock and have at it.
It's a lot of work but maybe it'll stop those bolt heads from snapping off inside your primary.

 

This makes a lot of sense to me.

 

Thanks MEGAWATT, I think I'll give that a shot. It does sound like a lot of work, but there is still about 2 feet of snow outside so I have plenty of time. Hopefully I'll get started this weekend.

 

Come to think of it, you probably should loosen the tranny-to-plate nuts when you loosen everything else. When it comes time to shim the tranny, tighten the tranny-to-plate nuts, then proceed with shimming the plate-to-frame bolts.
This will ensure the transmission aligns properly.
Do you know if your bike has been in an accident? I'm just wondering if the frame might be a bent a little. This procedure will take care of any minor tweak in the frame. I believe there are very few, if any, bikes that wouldn't benefit from checking this stuff when ya have it pulled apart for engine/transmission work.

 

I'm not sure if the bike has ever been into an accident before. I'm just going to follow your procedure and see what happens.