1966 427 Engine Compartment Clearances

[Everett Ogilvie]

A recently acquired '66 L72 car puzzles me with respect to clearances in the engine compartment. The clearance between the fan and the frame crossmember is about 1/16" at the closest point (the closest point is not directly at the bottom, but a little towards the passenger side). The clearance between the driver side exhaust manifold and the A-arm is almost zero - it looks like it has actually touched a few times (there are several alignment shims, but not excessive). The clearance between the bellhousing and the tunnel is about 1/8" on the upper driver side of the bellhousing. The clearance between the shift linkage and the top of the tunnel is almost zero.

Here are the specifics - the fan is original, the right part number, and the right diameter. The fan clutch is new and correct. Motor mounts are correct, non-locking, and appear to be in good shape. The bellhousing is original - the 444, specific to '66 only (I think the 444 is larger diameter than the '67 housing). The shifter linkage is in the standard long-throw position which positions it closer to the tunnel. The engine, trans, and bellhousing are the originals. The frame is original, not bent, car not wrecked, etc.

This trans/motor is stuffed in there, with no room to spare! My other '66 L72 has more clearance at the fan (3/4 to 1") and at the A-arm, which makes me think that on that car, the back end of the trans is "lower", which tips up the front of the engine, giving more clearance for the fan and the exhaust manifold at the A-arm. On the car with the tight clearances, it appears that if the tail end of the trans was lowered it would tip up the front of the engine, buying some fan and exhaust manifold clearance. It does NOT appear that "raising" the front of the engine via the front mounts could be done because that would drive the top of the bellhousing and the shift linkage into the tunnel.

Is there a procedure for "adjustment" of the trans mount to position the engine with the correct attitude (shims, etc.)? After comparing the two '66's and a few 67's, the 66's appear to be a tighter fit, probably due to the unique bellhousing. However, the difference between my two 66's leads me to believe that the motor mounts (possibly the trans mount in particular) are the root cause of the clearance differences. Any thoughts or similar experiences with 66's? 1/16" fan clearance can't be a good thing...

[Gene M.]

Re: 1966 427 Engine Compartment Clearances

How thick is your tranny cushion mount? I would also assume that your drive shaft is close to the tunnel if you have too thick of a tranny mount. Another possibility is the frame cross member under the tranny bent or been rewelded?
Are all the body cushions securing the body to the frame correct? Correct fan diameter? Are the cushions inplace for the radiator? More than 4 thick alignment shims is excessive. Just as a frame of reference are the exhaust pipes fitting thru the frame x-member centered in the opening and do the pipes attach squarly with the exhaust manifolds? Hood clearance OK?

[Everett Ogilvie]

Re: 1966 427 Engine Compartment Clearances

Thanks for the response Gene. Actually, the fan clearance to the crossmember is not related to radiator mounting, nor body mounting, although bellhousing to tunnel clearance could be related to body mounting. I believe the bellhousing clearance is tight because of the unique '66 housing. I will check the driveshaft to tunnel clearance. I have not measured the thickness of the trans rubber mount yet, but I will compare it with the other '66 car.

It really appears that if the rear of the trans was lowered, the fan to crossmember clearance would increase (and there is plenty of extra clearance between the fan and the top of the shroud, so that would not be a problem). Lowering the rear of the trans would also increase the bellhousing to tunnel clearance. It would change the driveshaft angle. To answer some of your questions - the fan and clutch are correct, so the fan is in the right postion relative to the engine - it is not in the right position relative to the crossmember. The pipes are pretty square within the crossmember holes. The trans crossmember does not appear damaged, bent or re-welded. I think the key here lies in the rear trans mount.

[Joe L.]

Re: 1966 427 Engine Compartment Clearances

Everett-----

Just a couple of points:

1) Aftermarket-type motor and transmission mounts are often configured a bit differently than GM. There are MANY differently-sourced mounts out there and, consequently, the number of possible "variations" is quite large. The GM mounts are the best and, also, the most expensive. The GM motor mounts, of which only the locking style are available under GM #6258154, GM list for $62.32/each. The transmission mount, currently available under GM #22188495 and identical to the original, GM lists for $150.09 (yes, that's what I meant). I don't know if the mounts are the problem in your case, but if they're aftermarket, they could be.

2) The "444" bellhousing is identical to the later "621" bellhousing except for the configuration of one of the reinforcing ribs on the upper driver's side. The "444" and "621" are both designed for 14" flywheels and are, consequently, larger than the "383" or "403" bellhousings used for most other mid-year applications with 12-3/4" flywheels.

[Everett Ogilvie]

Re: 1966 427 Engine Compartment Clearances

Thanks Joe. The difference of the rib on the bellhousing explains why the clearance is so tight in that area - my guess is that they experienced clearance issues with the 444. The engine mounts on the car are the non-locking type - I do not know if they are originals or replacements. I compared them to some aftermarket reproductions and they "appear" the same, but, as you mentioned, who is to say how good the reproductions are?

[Joe L.]

Re: 1966 427 Engine Compartment Clearances

Everett-----

Yes, the "621" reinforcing rib in question was wide and flat to improve clearance. The same rib on the "444" was just like the other ribs on both bellhousings. The "444" may have been used on VERY early 1967s, but it was replaced by the "621" thereafter. The "621" then continued to be used through 1981.

[Bill Stephenson]

Re: 1966 427 Engine Compartment Clearances

Everett,

------I wonder what kind of use this car had during its lifetime?I have often heard that hard use,such as racing etc.could actually close up the distance between the upper A-frame mounts.The frame actually collapses slightly.The extra weight of the big block engine could help excaberate this phenomenon.Have you ever taken out the motor mount bolts.You could get an idea of your problem if they slip in and out or were forced in.I also might take a close look at the mounts to see if they have been modified in any way to get them to bolt in.With all this said,I have not ever seen a frame with this problem,though I havent been actively looked for it either.I do know that almost all SCCA style Corvettes nowadays have a spreader bar that runs between the upper A-frames.They must be there for a reason.Does this idea have any merit,or am I all wet as usual?
------By the way is your shift linkage mounted to the trans or the frame?............Bill S

[William C.]

Re: 1966 427 Engine Compartment Clearances

You are correct Bill in the possibility of bending the front saddle during racing. I saw many race-prepared C-2 and C-3 cars in my NCCC racing days during the mid and late 70's. The added crossbay was pretty much SOP for the heavy competition set.

[Everett Ogilvie]

Re: 1966 427 Engine Compartment Clearances

That sounds pretty scary Bill - I hope that is not the case with this car. I don't think the car was subject to this kind of use. The car has low miles (I know, they could all be 1/4 mile at a time), original riveted ball joints, the rotors are still riveted, etc. All body panels are original (body reportedly never off frame), it does not look like it has been wrecked, and the frame has no visible signs of damage, or repair. At any rate, I think I can take measurements on the frame to verify that it is straight - I believe the AIM has reference dimensions. The motor mounts appear "normal" when compared to Paragon's reproduction non-locking type. With the reproductions in hand, we did a visual comparison with the mounts on the car, and they look OK but more measurements are needed.

My biggest initial concern is the lack of clearance between the fan blade and the front crossmember. My first impression was that if the front motor mounts were sagging (worn), new mounts would raise the engine and increase the clearance. But after observing the minimal clearance between the upper bellhousing and the tunnel, raising the front of the engine may not be an option. That led me to think that if the rear mount at the trans was lowered, it would "tip" the engine (with the front motor mounts as the fulcrum point), giving more clearance up front for the fan, with the added benefit of more clearance at the bellhousing - assuming that the driveshaft angle is acceptable.

[Wayne W.]

Re: 1966 427 Engine Compartment Clearances

What you are going to find is that the engine mounts, those coming off of the frame are bent, or out of position. You should do some investigation and measuring in that area. This is also naturally tied to the control arm mounts. Raising and lowering the transmission mount will not affect the height of the fan much. I see a lot of them that are wrecked, rusted or just torqued out of shape. I see them that have had a little air time like the Dukes of Hazzard have this problem. When you pull on them with a frame machine, the engine pops up and down like a Yo-Yo.