long post, odd problem, need help please on a '78

[Barry K.]

hi all

this is a strange one and it has me baffled.

2 years ago when I got my '78 it only had an original 9700 miles but it had been neglected and the last owner left it out in the driveway for the previous 2-3 years under a plastic tarp.
To clean it up properly and make it presentable again required pulling the motor out to repaint the block and all parts and to clean up the surface rust from the front of the frame and repaint the frame.
Part of the job also required removing the core support to clean that up and repaint it. The car sat approx 4 weeks on jackstands with the core support removed. I noticed no droop from the front end while the core support was out based on the panel gaps at the cowl and front of the doors from this though.
When reassembling the motor I put on brand new motor mounts since the rubber on the original mounts was beyond reusing.

After reinstalling the motor, core support, radiator, etc the fan shroud was not fitting correctly. Once bolted into place it was sitting so low it was causing the fanblade to hit on the top of the shroud, and yet the bottom of the shroud wouldn't reach down far enough to go into the clips designed to hold it at the lower portion of the core support.
Assuming the issue was it hitting the fan was caused by the nose drooping from not being supported for a month I corrected the issue by loosening all 6 of the core support side bolts, placing a jack under the core support and jacking it up to raise it to gain clearance for the fan than tightened the bolts back up before lowering the jack down. This gave me some working clearance for the fan although there is suppose to be about 1/2" of clearance or so and the best I could get was between 1/16" - 1/8". Enough to allow the fan to operate without hitting the shroud but not as much as it's suppose to have.
Compounding the problem is that the air intake duct for the aircleaner goes over the shroud and radiator and it's so tight that when the hood is closed it pushes down on the air duct causing that to push down on the shroud reducing the very little clearance I have to the fan. It's enough that just power braking the car or if I hit a dip certain ways and the frame flexes at all you can hear the fan start to rub the shroud.

I've tried everything I can think of to get the fan/shroud clearance that i'm suppose to have but nothing works. I've tried re-jacking up the core support more but there is no more of the very little adjustment there was, i've tried loosning the bolts and readjusting just the shroud but there is no play in the mounting bolts to allow adjustment there, I've confirmed that the radiator is fully seated in the rubber seats in the core support, etc.
The big issue here is that I need to raise the shroud to gain clearance for the fan but any amount of lift on that simply gets lost when the hood is closed and pushes down on the air duct which pushes back down on the shroud.......

The only other thing I can think of is the way the motor is sitting rather than the way the core support / radiator / shroud sits. Is it at all possible that the new motor mounts would cause the motor to sit any higher than before?? Even though the old mounts had the rubber all deteriorated which is why i replaced them, there obviously was enough proper clearance for the fan when the car was brand new with brand new motor mounts back than so how could new motor mounts now cause an issue?

sorry for the very long post but didn't know any other way to describe the problem so it would make sense.

any ideas or suggestions are greatly appreciated

[John H.]

Re: long post, odd problem, need help please on a '78

Barry -

When you removed the radiator support, did you note the thickness of the shim pack between the bottom of the radiator support mounts and the frame and re-establish those shim packs when you re-installed it?

[Barry K.]

Re: long post, odd problem, need help please on a '78

John
when I removed the radiator and core support there were NO shims at all.
Didn't really think about it at the time but now that you mention them it is a bit odd that there wasn't as I've heard of them mentioned numerous times.

Besides, if there were shims, which there wasn't, or I added them now, that would raise up the core support and radiator and shroud but that would also just cause the hood to press down on them even more when the hood is shut which is the really confusing issue. That's why I started to consider how the motor is sitting rather than the shroud - perhaps the motor is sitting too high causing the fan to be too high in the shroud opening

[Wayne W.]

Re: long post, odd problem, need help please on a '78

Sounds to me like you got some thick motor mounts.

[Terry M.]

Re: long post, odd problem, need help please on a '78

I would wager the replacement engine mounts are not the same height as the OEM mounts. That is what has raised the engine and given you fan clearance problems. Wish I had a solution for you though.

[Barry K.]

Re: long post, odd problem, need help please on a '78

that's where my thinking was going also, that the motor mounts are not correct. considering I don't have an engine hoist, I borrowed a buddies when I had to pull than reinstall the motor at the time, it's going to make changing them out again a bit of a problem unless I can get the hoist back for a day.

What makes it more difficult now is that for some strange reason I can't find the reciept in my file on the car for the new motor mounts to double check the part number. I have every reciept for every penny I spent on the car down to the most misc item but I can't find the one for the motor mounts! go figure
Regardless, I suppose it's very possible that any aftermarket or repro mount could easily be off from the original specs, especially based on my experience with other repro parts I've had to deal with between this car and my '65.

[Dave F.]

Re: long post, odd problem, need help please on a '78

Here is another thing to consider. The core support on my '68 has mount points on each side that bolt into metal imbeds on the inner fender portion of the nose, and it is possible those imbeds have corroded to the point where they have lost their structural integrity and have "slipped" upward allowing the nose to sag at the core support location. This is what happened on mine and I had to replace those imbedded mounts. Check your assembly manual and you might see what I am discussing here.

[Wayne P.]

Re: long post, odd problem, need help please on a '78

You don't need a hoist. Just jack it up with a floor jack and change from the bottom.

[Dave F.]

Re: long post, odd problem, need help please on a '78

I read the entire thread. I think the engine is too high. I certainly like the "imbedded supports have slid" idea, but this would seem to account for only the lack of clearance between the hood and shroud, and not the fan and shroud.

Is there a way to take a measurement between the pan and crossmember perhaps, that you could post and perhaps another owner might be able to compare with on their car? My experience is that if the mounts are too thick,(wrong part) it's tough to get the long bolts in them, because the holes move furthur apart. It's usually pretty obvious that you have the wrong mounts.

Sorry, not much help. But please post what the final solution turns out to be.

Yep, you're correct - the imbeds would have had to drop (then somehow wedge) to cause an interference between fan and shroud. Good catch.

[Joe L.]

Re: long post, odd problem, need help please on a '78

that's where my thinking was going also, that the motor mounts are not correct. considering I don't have an engine hoist, I borrowed a buddies when I had to pull than reinstall the motor at the time, it's going to make changing them out again a bit of a problem unless I can get the hoist back for a day.

What makes it more difficult now is that for some strange reason I can't find the reciept in my file on the car for the new motor mounts to double check the part number. I have every reciept for every penny I spent on the car down to the most misc item but I can't find the one for the motor mounts! go figure
Regardless, I suppose it's very possible that any aftermarket or repro mount could easily be off from the original specs, especially based on my experience with other repro parts I've had to deal with between this car and my '65.

Barry-----


As Wayne mentions, you don't need an engine hoist to change the mounts. Just loosen the rear mount and jack up the front of the engine enough to get each side mount out.

However, the BIG problem is going to be getting the right motor mounts. As I have discussed previously, all of the mounts that are currently on the market are foreign-manufactured. I have not seen one yet that I'd want to use.

[Barry K.]

Re: long post, odd problem, need help please on a '78

Here is another thing to consider. The core support on my '68 has mount points on each side that bolt into metal imbeds on the inner fender portion of the nose, and it is possible those imbeds have corroded to the point where they have lost their structural integrity and have "slipped" upward allowing the nose to sag at the core support location. This is what happened on mine and I had to replace those imbedded mounts. Check your assembly manual and you might see what I am discussing here.

i understand where you are referring to. Other than the surface only rust I had to clean off the front section of the frame the structural aspect of the car was absolutely perfect. I found nothing at all corroded anywhere on the frame or body of the car (except the rubber of the original motor mounts)

[Barry K.]

Re: long post, odd problem, need help please on a '78

ok, good news that that I won't need an engine hoist to change mounts if I floor jack will work.

Now I just need correct mounts but it sounds if that is going to be an issue. Just wonderful. you would think the repro manufacturers could get something as simple as an engine mount correct. SIGH

Joe Lucia, I haven't checked yet but do you know if the motor mounts are still available from GM thru their dealer parts counter and if so are they typically too thick also or just the aftermarket vendor mounts? If so, any suggestions? There surely is no point to replace these mounts if I'm going to send up with the same problem

I think while i'm at Carlisle this year I better search around for any NOS motor mounts

[J M.]

Re: long post, odd problem, need help please on a '78

Barry
Back in 2005 when I rebuilt the 327/350 in my 66, I got replacement motor mounts from GM. The part number was 6258154. Don't know if they are still available but they were not cheap. I have one extra if you need it.

[Barry K.]

Re: long post, odd problem, need help please on a '78

Barry
Back in 2005 when I rebuilt the 327/350 in my 66, I got replacement motor mounts from GM. The part number was 6258154. Don't know if they are still available but they were not cheap. I have one extra if you need it.

thanks for the part number. I'll try to look it up to see if it references to the same for a '78.

BTW, is ANYTHING cheap fora Corvette?

[John L.]

Re: long post, odd problem, need help please on a '78

Barry do you have a L-48 or L-82 in your 78?
I was thinking I could measure my 79 L-82 for the clearance of the Harmonic Balancer Clearance to the frame and compare it to yours. My mounts were replaced 8-9 years ago and I didn't have any fit problems then or now (I think they are GM). I'll be home from work in a few hours and will post what I find then. I also have the originals somewhere I'll try to find them.