heli coil question

[nonhog]

resealing a 66 Corvair oil pan and wouldn't ya know it, the last bolt pulled threads out. I have the proper kit to fix but have to wonder about leaving the freshly sealed gasket and pan in place and fix that way. Any reason it won't work?

 

[The Cobbler]

you're saying the pan & gasket are in place, you want to helicoil the damaged thread?
I don;t see any reason why it won't work. but I would do it as soon as you can

 

[nonhog]

Yep! Not so easy getting replacement gaskets (quickly) for Corvairs.

 

[MP&C]

Any threads still in there deeper where a longer screw might reach?

 

[CapriMikeC]

It's possible the through hole in the oil pan flange will need to be opened to permit the helicoil to fit. For example, if the bolts are 1/4"-20, the helicoil will be a bit more than 5/16" outside diameter.

To get the helicoil started in the drilled hole, standard procedure is to chamfer the hole with a 120 degree bit. This may be difficult to access with the pan & gasket in place.

 

[Ricky Joe]

Only risk is that it might drill the pan a little oversize. Other than that, if access is good, you should not have any problem. Modify a fender washer, if necessary.

 

[MP&C]

It's possible the through hole in the oil pan flange will need to be opened to permit the helicoil to fit. For example, if the bolts are 1/4"-20, the helicoil will be a bit more than 5/16" outside diameter.

To get the helicoil started in the drilled hole, standard procedure is to chamfer the hole with a 120 degree bit. This may be difficult to access with the pan & gasket in place.

Should be a 17/64 (.2656) drill bit for 1/4-20 helicoil. Very likely the hole in the pan already has that amount of clearance.

 

[Monza Harry]

The size Robert referenced is the tap drill, the coil itself will be larger by approximately the same over size amount, 1/64th" quoted so 2x that is 1/32nd" which is = to what the normal clearance hole would be [+1/32nd" or 0.281"] stampings tend to be a tad looser with that sizing, so the coil should fit through if he can maintain concentricity to the original hole. That isn't easy with threaded hole as the thread is a stepped surface. I have never succeeded by hand, close(ish) yes, but with a machine no problem. Under the car facing a shower of hot chips, odds aren't getting better (a face shield and a welding beany and a towelover your neck will be your friends here). I agree possible, yes a challenge OH YEAH! To start I would take a small (⅛) cylindrical burr and create a small circular counterbore of your tap drill size just deep enough to get the whole drill diameter in and it should follow pretty well then. OP keep us updated PLZ! If that needs additional clarity ask away I'm sure I (we this forum has many qualified metal cutters with mechanical experience +!)can help. Harry

 

[zmotorsports]

It's possible the through hole in the oil pan flange will need to be opened to permit the helicoil to fit. For example, if the bolts are 1/4"-20, the helicoil will be a bit more than 5/16" outside diameter.

To get the helicoil started in the drilled hole, standard procedure is to chamfer the hole with a 120 degree bit. This may be difficult to access with the pan & gasket in place.

This would be my only concern. If the hole in the pan is large enough to allow the hole to be chamfered and the insert to fit through it then I wouldn't hesitate to do it that way, otherwise the pan will need to be dropped. I don't know that I would drill out the pan hole larger but I guess that could be another alternative if the insert won't fit through the existing hole.

 

[bwringer]

I'm not even a pro mechanic, but I've encountered two aftermarket oil pans with one hole in the wrong place.

These were pans sealed with RTV and no gasket from the factory, so I shrugged and left that bolt out. No issues.

If you have some sort of sealer on the pan gasket, odds are strong that one missing bolt won't hurt a thing.

But if it'll bug you for ever and ever... well, you know what to do.

 

[danielbuck]

could try simply tapping the next size up and using a larger bolt. I've done that on boogered exhaust manifold threads in steel heads.

 

[nonhog]

Thanks for the thoughts! I question the quality of aluminum GM used on the Corvair. Its a blind hole but I feel like it could be drilled through but not sure it would help. It may be ok as is. But it's a Corvair, it's hobbies inc. "leaking oil" among other things! LOL So I figure don't give it a chance to leak.

 

[APEowner]

I'd pull the pan and even though it's not original I'd use RTV instead of the cork gasket.

 

[Honch]

Since it’s not installed I would JB weld the hole closed, drill and tap it to the original size. Fairly easy and quick, plus it’s completely reversible if the fastener won’t hold the required torque. This would prevent the need to oversize the hole in the pan or remove it.

I think JB weld has a thread repair product too, I’m not familiar with it.

 

[Ricky Joe]

Just take toothpicks and stuff them in the hole and force the bolt in. Voila!

 

[senlow]

Just take toothpicks and stuff them in the hole and force the bolt in. Voila!

That's just as good as JB Weld.

 

[The Cobbler]

Just take toothpicks and stuff them in the hole and force the bolt in. Voila!

maybe not toothpics, but a pc of flattened copper wire has been known to aid stripped out threads

 

[nonhog]

I have an extra oil pan. Think I will measure the hole and see how far off I am? (if at all?)

 

[Cluster]

Personally I'd avoid a Heil-coil, bet is that you could go the next higher size thread (eng or metric) that would allow a minor thread dia just large enough to drill out most the previous threads.
Ex.
If stripped thd is a 1/4-20 the drill size for helicoil is 17/64 (.266). I hate heli-coils, think it best to just go up to a std 5/16-18 with minor dia of .257... may need to enlarge the pan thru hole to clear a .312 bolt
If you do need to enlarge the pan thru hole, rig a tubilar spacer or depth ring on drill to prevent it for beinning 'sucked' too deep, blowing your new minor dia out. matter of fact this should also be done when drilling new minor dia to prevent drill being 'sucked' into oil cavity or worse.
Paint the odd ball bolt and mark pan hole location for future ref.

 

[nonhog]

I did the heli coil and it seems great. Had room with the stock pan in place. I'm happy!