90hp V4 Surging

[emmo1210]

Hi Guys,

Have been having a surging problem on 90 v4 1990 motor since rebuilding (had cylinders rebored)

Using aerosol I traced the air leak to what i thought was a bypass cover leakage.

Having thought it was duff bypass cover gaskets, I made several attempts to replace the gasket to no benefit.

I now realise that as the bypass covers run so close to the crankcase split, that it is probably the crankcase that is leaking air.

Is there any easy fix for this without having to strip the engine totally down again?

I read on another thread a guy who used JB weld to seal the leak on the outside, would this be a suitable fix.

Appreciate any suggestions from you more experienced fellows.

Emmett

 

[jbjennings]

Re: 90hp V4 Surging

Is it surging on idle or at high speed, or both?
If at idle, try spraying some propane gas from a propane torch around the crankcase halves, carb body, intake, etc. If the motor smooths out, you found the leak. IF it were crankcase halves, I'd probably just take it apart and use some of the proper sealant on the seam, although the jb weld would almost undoubtedly work for a long time.

 

[emmo1210]

Re: 90hp V4 Surging

Hello jb, Thanks for reply. Yes have already sprayed propane around crankcase and found where it smoothed motor out. At this point it could have been either a bypass cover or crankcase. I have now concluded that it is indeed the crankcase that is leaking.
Didtn really fancy pulling the whole motor apart again having only rebuilt it (obviously poorly) . Would the powerhead have to be removed from cowl or could it be split just by removing intake manifold off? Also what is the proper sealant? Aviation gasket compound?

Thanks
Emmett

 

[jbjennings]

Re: 90hp V4 Surging

Yes, you'd have to remove the powerhead. But if you just bite the bullet and make yourself do it, I think you could do it easily in one Saturday afternoon, especially since you've done it already. I know it's a pain, but if you ever decide to sell it, you don't want jbweld on the darn crankcase, plus you don't want to have to think about it being there every time you fire it up. Keep in mind, you're hearing this from somene who uses a '73 65 merc with jbweld holding together completetly broken water jackets.....
I don't know what sealant to use, but I've used permatex gray before. I think 3M makes some good stuff to use but can't remember the exact #. There have been some old threads here that F_R told what sealant to use. I'll see if I can find one.
Later,JBJ