Engine Mount Alignment Help

[CowboyGrin]

In early stages of a frame-off resto on my '73 and started a mockup of the drivetrain before doing repairs/cleanup of the frame and rebuilding engine. Specifically wanted to see what options were available for clocking Atlas t/c with a 5.0 and an AX-15 to hopefully avoid notching frame.

Currently using heavy-duty engine mounts from James Duff (https://dufftuff.com/product/early-bronco-heavy-duty-motor-mounts/) and crossmember from Advanced Adapters (https://www.advanceadapters.com/4770). With engine situated nicely into frame brackets I'm missing crossmember holes by 1"-2" (see photos). Measurements from the passenger side frame rail confirm the driveline is angled from passenger side at front towards driver side at rear.

Stumbled onto a thread (https://classicbroncos.com/forums/threads/4r70w-crossmember-trouble.316887/) with similar troubles that suggest ditching the extreme mounts for stock style as a solution. It seems that the misalignment using the stock style would twist the rubber and cause premature failure. The heavy duty mounts appear to be nicely made and likely to fair better in the long term. Could one clearance the holes in the frame brackets (I estimate ~1/4" on the front of the driver side and rear of the passenger side will be enough) and use a heavy plate washer with the bottom nut? Or is this just asking for other problems?

 

[BOBS 2 68S]

I used the AX-15 kit from WH and it bolted in with no adjustments to frame or cross member. Have you bolted the transfer case up to see how it fits?

 

[CowboyGrin]

I used the AX-15 kit from WH and it bolted in with no adjustments to frame or cross member. Have you bolted the transfer case up to see how it fits?

Not yet, didn't want to hang that kind of weight on the end of the transmission without the transmission mount bolts seated in the crossmember holes properly. I'm positive the transfer case wouldn't fit well anyway. Most diagrams show the driveline centered 10.75" off the passenger side frame rail while I'm closer to 12" at the rear of the transmission. If anything, I was hoping to be less than 10.75" to help with clocking the Atlas.

 

[Oldtimer]

This seems to be a common issue with heavy duty motor mounts.
The mounting holes in the Bronco frame are in the same plane, front to back.
I can't find dimensions of bolt holes in SBF for the motor mounts.
The motor mounts are not symmetrical and the instructions say "engine mount plate can only be installed one way". Instructions say nothing about left or right mount.

Question: When both motor mounts are bolted to block are studs/bolts that go into frame holes in the same plane, front to back?

 

[CowboyGrin]

This seems to be a common issue with heavy duty motor mounts.
The mounting holes in the Bronco frame are in the same plane, front to back.
I can't find dimensions of bolt holes in SBF for the motor mounts.
The motor mounts are not symmetrical and the instructions say "engine mount plate can only be installed one way". Instructions say nothing about left or right mount.

Question: When both motor mounts are bolted to block are studs/bolts that go into frame holes in the same plane, front to back?

View attachment 893488

Correct, the mounts are not tagged L/R and can only be installed one way. They appear to be universal/interchangeable due to the engine mount bolt hole locations on the block due to the cylinder offset:

I haven't checked if the frame hole bolts are in the same plane. I'll add it to the things to verify along with the frame bracket locations using Steve83's frame diagram. Thanks.

 

[fluffybunny]

Looking at the kit on AA's site, the transmission plate is slotted for left/right movement. Can you loosen the plate and slide it towards the passenger side?

 

[CowboyGrin]

Looking at the kit on AA's site, the transmission plate is slotted for left/right movement. Can you loosen the plate and slide it towards the passenger side?

Yes, it does. Hard to tell from the photos, but the plate is shifted as far as the slotted holes will allow. Only about 1/2” to 3/4” can be picked up in either direction.

 

[fluffybunny]

I would figure out a way to temporarily support the trans and bolt up the tcase and see if it's too cocked for the driveline. If it looks like it would work, I would pop new holes in the cross member and bolt it up. If it won't work, I would look at putting some relief cuts in the driver side motor mount brace (if that's what you call the protruding arm off of the frame) and then pulling the driveline into position, and weld it up by a competent welder. I would not clearance the holes for the motor mounts. Good luck with it.

 

[fluffybunny]

Please keep us updated. I would like an AX-15 some day so any info might be good for knowledge.

 

[Yeller]

Shouldn’t be any issues clearancing the motor mount frame holes for alignment. we do it all the time to shift over the transmission the 1-1/2” or so needed to clock an atlas flat. To move that much, it’s only about 1/8” of clearance added to the motor mount holes. This issue comes up time to time due to the loose tolerances of the frame, the original mounts would flex enough to eliminate the issue, the extreme mounts don’t have that flexibility.

 

[bax]

The holes on the advanced adapter crossmember are not correct. The need to be re drilled.

 

[Yeller]

There’s the voice of experience

 

[Steve83]

I'll add it to the things to verify along with the frame bracket locations using Steve83's frame diagram. Thanks.

Did you begin by checking the frame squareness before dropping the engine onto it? You need to compare diagonals, as that diagram indicates.

(click this text)

The holes on the advanced adapter crossmember are not correct. The need to be re drilled.

That can also be checked using the frame diagram - the center of the trans mount pattern (and the trans output shaft) should be 1" offcenter, just like the crankshaft.

 

[CowboyGrin]

Apologies for the late update. Still had a few holiday obligations and indulging left to do.

We spent a couple hours of verifying frame and engine bracket dimensions. Amazingly, the engine brackets are spot on. Steve83’s diagram was invaluable using the 1 pixel to 1/16” scaling.

James Duff‘s tech support reached out with some things to try. Specifically, swapping the upper & lower mounts and switching sides of the engine block to account for fabrication tolerances in both the mounts and block. After about the third attempt, we found a combination that straightened up the engine to run parallel to the frame and with the center of the driveline 10.75” to the inside of the passenger side frame rail.

Bax is 100% correct. The AA crossmember has the center of their holes 9.75” from the passenger frame rail for some reason. I did not catch this before but found a thread on this site with similar findings when I was searching for sanity. Unfortunately, the transverse slots in the upper transmission mount don’t allow for enough side movement to use the fabbed holes.

Strangely enough, the holes appear to be where I need them to clock the transfer case up inside the frame rails. As mentioned by many, the heavy duty mounts offer little movement to cheat the tail end over so I’ll have to deal with the frame brackets if I want to keep the the mounts. At this point, I don’t believe clearancing the bracket holes or notching the brackets are the best solution to keep the plane between the frame bracket and mount in contact. Right now I’m leaning towards cutting off the frame brackets entirely and rewelding to frame rotated slightly to allow clocking the transfer case. Alternatively I could go back to stock style mounts, but I’m convinced I asking for trouble down the road by preloading the rubber with the twist needed.

Thanks to everyone for their suggestions and insight.

 

[Jarrett h]

I had issues w/ the WH HD mounts just bolting to my motor (dart block), but experienced clearence issues all around because it raised the motor up. Raising the motor causes everything to pivot up which changed the angle of the trans/transfer case & pushed my valve covers into the firewall.

The JD mounts are supposed to eleivaite the issues I had but I still don't understand why all the mounts i looked at have the same offset for the left & right side which in turn pushes the motor closer to the driver side.

 

[jamesroney]

Apologies for the late update. Still had a few holiday obligations and indulging left to do.

Can you please post of pic of your front driveshaft when you are done? When I did this using the D20 and NV, there was barely room for the front driveshaft to drop thru the crossmember. I remember fighting the holes in the crossmember, but it didn't matter when the driveshaft wouldn't fit. I always wondered how the atlas 4sp would deal with that...since it sits farther back.

 

[CowboyGrin]

Did you begin by checking the frame squareness before dropping the engine onto it? You need to compare diagonals, as that diagram indicates.

(click this text)

Yes, everything checked out on the squarenes. I also verified dimensions at each of the body mounts (longitudinal, transverse, diagonal, & vertical) using the pixels.

I was really concerned about the frame because there are a few mods from a PO that gives the impression it could have been wheeled hard. The only discrepancies found were the front body mounts at the radiator support are 1/2” high on the passenger side and 1/4” high on the driver’s side. Hoping that can handled with shims or a BFH.

The diagram is a huge help but I did find a problem: I initially pulled the vertical dimensions from the datum line using the pixels in the cross sections on the right to get a 1.875” drop at Sec F. On the actual frame, I measured a 4” drop and nearly had a heart attack. Took me awhile to realize the side view with the section cut marks on the bottom left appeared different. It’s pixels came out to 4.125” so I call that good enough. I suspect the datum line is off a bit in the section views.

 

[CowboyGrin]

Can you please post of pic of your front driveshaft when you are done? When I did this using the D20 and NV, there was barely room for the front driveshaft to drop thru the crossmember. I remember fighting the holes in the crossmember, but it didn't matter when the driveshaft wouldn't fit. I always wondered how the atlas 4sp would deal with that...since it sits farther back.

Yeah, I noticed that and it could be a battle for another day. Need to get it clocked and get the new suspension & axle in place to know for sure but will definitely share what I find. Could be awhile, have a lot of work ahead of me with this frame. At least now have confidence the frame is generally true.

 

[bax]

I love it when this happens. (Bax is 100% correct.) I have an ax15 and an atlas mocked up in the shop right now. I will have to go look but I think my atlas is higher than yours. Is the 4 speed atlas wider than the 2 speed?

 

[bax]

Nope I just went out and looked and yours is a little higher than where mine is. You win.