Problem on the road today

[Michael M.]

Had my 68 out this morning for a drive. Right after I punched it hard, I heard a noise from the engine compartment and pulled over immediately.

Result: Apparently, the engine rotated enough for the fan to contact the fan shroud, which in turn bent the fan, which in turn took out my radiator.

Engine is an L36 BB but with modifications makes about 475-500hp.

Now my questions:

1) a new fan shroud is needed, did all 68's use the same fiberglass fan shroud?
2) My fan was a 17 1/2 repro fan from Paragon, was the fan too large
3) I will inspect the motor mounts, but can anyone else think of reasons for the fan to hit the fan shroud?

THanks for any replies.

[Dick W.]

Re: Problem on the road today

If the left motor support is not broken, after you put it back together, check that the fan is centered in the shroud. You could have the core support to high, low, left, or right.

[Domenic T.]

Re: Problem on the road today

That is tipical of a broken left motor mount.

The test is to hold the brake in gear and give it gas and see if the left side of the engine lifts.

Easy with an automatic but with a stick you need to block the wheels or use the emergency brake to hold the car back.

Be carefull because that problem caused a lot of accedents because it would bind the throttle open when the left side lifted.

Your car should have safety mounts on it but it will still lift enough to do damage.

DOM

[Ronald L.]

Re: Problem on the road today

68 is a One-Year-Only shroud.

[Michael M.]

Re: Problem on the road today

Thanks guys. The motor mounts aren't that old, but they'll get replaced anyway. So motor mounts are the culprit for sure?

I see Volunteer Vette lists a fiberglass shroud for all 68's. Did all 68's use the same shroud? Or did all BB 68's use the same shroud?

[Ronald L.]

Re: Problem on the road today

Michael - see above, 68 BB one-year-only.

[Paul J.]

Re: Problem on the road today

So motor mounts are the culprit for sure?

...Yes....

[Michael J.]

Re: Problem on the road today

"Engine is an L36 BB but with modifications makes about 475-500hp"

"So motor mounts are the culprit for sure?"

Sounds like the stock motor mounts couldn't take the new torque and HP.

[Gary R.]

Re: Problem on the road today

Hi Mike
I had fairly new rubber mounts on my 69 years ago and one day after working on the hurst shifter I drove it without the shifter boots in place. I clearly saw the trans twist shifting, the fan never hit but it is the smaller one for a SB if I recall. Anyway I removed the LH mount and it was sheared in 1/2 just the internal safety was all that was holding it together. I went to poly mounts. My son used the same poly mounts but he pushes his vette very hard and he found poly was loosening up after a year. He went to solids. My tame 300hp 72 is still good but I don't drive it too much.

Gary

[Michael M.]

Re: Problem on the road today

I will dismantle this weekend and report back. I highly suspect motor mounts (I can't think of any other reason, other than a misaligned fan shroud but it's been fine for a while).

Michael Johnson, I agree with you but I installed polyurethane motor mounts to handle the addiitonal torque and hp. I even installed a heat shield on the left side to protect it from the exhaust heat. We'll see.

[Michael M.]

Re: Problem on the road today

As promised I am reporting back on what I found when I dismantled the Corvette cooling system. As I stated in my initial post, radiator, fan and fan shroud were destroyed. Also, I found that the fan clutch came apart and the front plate with bi metallic spring was found in another area of the engine compartment. Based on the condition of the fan clutch, I've elected to also replace the water pump. Although it appears to spin freely, everything else is apart and I do not want a repeat of this problem due to a wobbly water pump.

I also replaced the motor mounts. The right side showed evidence of some heat damage but was not compromised. The left side (with heat shield) was in perfect condition. I replaced them both anyway. I was fully expecting the left mount to fall apart in my hand as I replaced it. Not so.

Now that engine mount failure has been ruled out, the only other thing I can think of is fan to fan shroud mis-alignment which only exhibited itself at high rpm (possibly as the fan flattened out). The engine (L36) was turning over 6,000 rpm at the time of the problem. I was using the Paragon reproduction of the GM [FONT='Tahoma','sans-serif']3888366[/FONT]

Once I re-assemble, I make sure there is PLENTY of fan to fan shroud clearance. Boy this was an expensive mistake!

[Ronald L.]

Re: Problem on the road today

Michael, get the correct fan too. LIC has the correct size if yours takes the 17".

Also, less pictures I'm not sure you have the correct fan shroud and or it could be assembled too small. Pictures are worth 1000 words.

In all it sounds like your clutch let loose and that was the real root cause. Save those original parts!

[Michael M.]

Re: Problem on the road today

Ronald, yes I will post pictures. This past weekend was a whirlwind. I'll snap some pictures and post this weekend. The car is a driver. None of the parts that were destroyed were original parts but I'm 99% sure I had the right stuff on it. I doubt the fan clutch caused all of this because that probably doesn't explain the bent fan blade and the damage to the radiator, but it is possible. Anyway, this is all speculation. Fact is I'll replace the parts and do what I can to not have a repeat performance. I was just really surprised that the motor mounts were not the culprit.

[Michael J.]

Re: Problem on the road today

I have often been curious about the repop fan clutches that pass muster for flight judging. I have had two new ones and neither show much of any difference in resistance with temperature differences. Now that flight judging is past and done for good, maybe a good fan clutch like from the NAPA line is in order. Anyone know of a good one that works, unlike the LIC types that don't?

[Edward B.]

Re: Problem on the road today

In all it sounds like your clutch let loose and that was the real root cause. Save those original parts!

Motor mounts may or may not have been all they should be, but from what has been posted it seems as if the fan clutch failed and the parts spiraled out of control from there on. If the car is to be driven it deserves a quality fan clutch rather than one of those "pretty" ones.