Engine mounting bolts

[dannyual767]

Okay, I thought that I'd use the standard hardware store stainless steel allen head bolts to secure my engines to their mounts. I've got two OPS .67s, a K&B .67 and .82 and my latest, an O.S. .21 RG-M. This O.S. has tiny holes in the engine mounting lugs that only a small 4-40 size bolt will fit in.

Anyway, I was told that stainless steel bolts are too soft to be used in engine mounting applications. In fact, one of my engine mounts came with regular steel bolts. Do you guys use regular bolts and just change them out when they rust or are there some other strong bolts that would work?

Danny

 

[bzubee]

Don't use the stainless bolts they will eventually break .

 

[dannyual767]

Don't use the stainless bolts they will eventually break .

Yes, thats what I was told today by Remy @ Aeromarine. I've been looking on the McMaster-Carr website and found some zinc plated, steel allen head bolts that look like they'd work pretty good. They seem to offer decent corrosion resistance.

 

[Mike Hughes]

Been using stainless since 90 and have not broken one yet. Use them in my 21 to 90.

Mike

 

[dannyual767]

Been using stainless since 90 and have not broken one yet. Use them in my 21 to 90.Mike

Okay, Mike, thats something else for me to think about. I'd like to just use the SS bolts that I've got without having to order special stuff from MMC. On the other hand, if I make an order, I'll probably just go ahead and order some zinc plated steel bolts. They don't really cost that much at all but I'm sure they're hard to find in a normal hardware store !

 

[piper_chuck]

Can't say I've ever broken a stainless bolt either. Perhaps they do break over time, but at $5-7 per hundred at McMaster-Carr, I can live with a few breakages.

 

[Krusty 181]

Ive been using stainless 4-40 caps heads to hold my 21's without a problem , just tap the mount and a little loctite on the bolt , never had a problem

Andrew

 

[Tom Foley]

Been using stainless bolts since 1980 , no failures in any size motor application . Whatever works !

 

[dannyual767]

Hmmmmm :unsure: . Mike, Chuck, Andrew and Tom; this is all very interesting. I'm now thinking that SS bolts will work just fine.

The reason that I called Remy @ Aeromarine was because the O.S. motor mount that I got from them was drilled and tapped for 6-32 bolts. My brand new O.S. .21RG-M has small holes in the mounting lugs that will only fit 4-40 bolts. Remy said that I'm going to have to drill out my engine's mounting lugs. I don't really want to do this and Andrew says that he's been using 4-40s for his .21s with no problem.

 

[dr gary turner]

Hmmmmm :unsure: . Mike, Chuck, Andrew and Tom; this is all very interesting. I'm now thinking that SS bolts will work just fine.
The reason that I called Remy @ Aeromarine was because the O.S. motor mount that I got from them was drilled and tapped for 6-32 bolts. My brand new O.S. .21RG-M has small holes in the mounting lugs that will only fit 4-40 bolts. Remy said that I'm going to have to drill out my engine's mounting lugs. I don't really want to do this and Andrew says that he's been using 4-40s for his .21s with no problem.

I have been using 4-40 SS bolts since 1980 and have had NO PROBLEMS. In fact they are in my SGX 21 hydro and Blackbird 21-hydro, I also use SS in all of my boats including a 101. Dr.T

 

[jetpack]

The only time I would hesitate on using 4-40 SHCS on a .21 is not using a tall SS washer with it. Some capscrews have a flair-out just under the head that can gouge out the lips of the holes.

 

[Mike Hughes]

An option to switch to 4/40 would be an helicoil. I think the 4/40 OD helicoil is an 8/32 thread. You would have to drill and tap the mount for the helicoil. You might be able to move the motor forward or aft and redrill new holes. I have been using 4/40 in my 21 and 45 engines for years.

Mike

 

[dannyual767]

I'm just not real pleased that these mounts from Aeromarine have holes drilled and tapped that are too large for the engine lugs :angry: . I don't think that I should be required to drill out my brand new engine's lugs just to get it to bolt to this mount. I wonder if I should just send the mount back to AM <_< ?

 

[jetpack]

Were the mounts specified as being drilled and tapped for your OS? If so they should be for your 4-40 size holes, I would return it. You should never have to drill out the mounting lugs for any engine...that is the wrong approach and not what the engine designers had in mind.

 

[Krusty 181]

I have to say that drilling out any of my engines would be the LAST thing i would do , i would think that if the manufacturer makes an engine with 4-40 holes , then they are quite happy for you to use 4-40 bolts ...

and i dont think they would like you to possibly weaken the mounting area by drilling the holes out to suit a particular mount

I would send it back ... and exchange it for one that works

Andrew

 

[Joe_Knesek]

I have to say that drilling out any of my engines would be the LAST thing i would do , i would think that if the manufacturer makes an engine with 4-40 holes , then they are quite happy for you to use 4-40 bolts ...and i dont think they would like you to possibly weaken the mounting area by drilling the holes out to suit a particular mount

I would send it back ... and exchange it for one that works

Andrew

I do it all the time (20 seasons). No problems unless you go overboard. They are drilled for metric screws & converting to SAE is not a big jump. I drill my 21 motors to allow 6-32 and my 67 motors to 8-32.

 

[dannyual767]

I have to say that drilling out any of my engines would be the LAST thing i would do , i would think that if the manufacturer makes an engine with 4-40 holes , then they are quite happy for you to use 4-40 bolts ...and i dont think they would like you to possibly weaken the mounting area by drilling the holes out to suit a particular mount

I would send it back ... and exchange it for one that works

Andrew

Andrew, I feel the same as you. I want to send the mount back to Aeromarine. However..................

posted by Joe,

I do it all the time (20 seasons). No problems unless you go overboard. They are drilled for metric screws & converting to SAE is not a big jump. I drill my 21 motors to allow 6-32 and my 67 motors to 8-32.

Remy from AM said that none of his mounts are drilled for 4-40 bolts. I like the idea of predrilled mounts because everytime I try to drill precision spaced holes, the spacing is always unprecise and stuff doesn't fit right :angry: :angry: :angry: . Nobody else that I know of besides AM sells predrilled engine mounts. Maybe I should just drill my engine's lugs out :unsure: .

 

[piper_chuck]

I've seen plenty of engine lugs with slightly enlarged holes.

 

[dannyual767]

I've seen plenty of engine lugs with slightly enlarged holes.

Yeah, there appears to be plenty of metal there to go just a hair larger.

 

[piper_chuck]

I've seen plenty of engine lugs with slightly enlarged holes.

Yeah, there appears to be plenty of metal there to go just a hair larger.

And you could have it done and mounted in about the same time it'd take you to pack up the mount to send back to AM.