Epoxy product recommendation to bond M8 stud into engine block

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West Coast

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The bracket which supports the FW pump and alternator on my VP 2003 is secured to the engine block via three M8 bolts. The bolts go into tapped holes in the block, but first go through a housing over the front engine bearing, securing the housing to the engine block in turn.

I had to remove the bracket last season to repair the pump. But, on replacement, I found that thread in the block for one of these bolts has stripped.

Given the block is the far side of the housing, I cannot re tap for a bigger bolt, or put in an insert without removing the housing etc. so, an idea from a wise fellow forumite is to epoxy bond a M8 stud into the block.

Can anyone recommend a suitable product for this, or a company / supplier who can give good advice and a suitable product?
 
As you ae using a bolt rather than a stud, there may still be some serviceable thread at the base of the hole, beyond the normal bolt's reach.

I would try using a longer bolt to find out. Full strength is obtained in 1.5 x dia or about 12mm, but even a few turns may be sufficient.

If you do have some decent thread then I would use a high strength locking compound such as Loctite 270, using a piece of threaded studding, and don't overdo it on the final tightening. Use a syringe to squirt the compound into the hole and smother the thread. Wind in the stud to the base of the hole and leave to set for a few hours. Use a nut instead to secure.

Problem with epoxy is the lack of surface area to establish a decent strength bond upon.
 
I had the very same experience on a VP2003. In my case I could solve it by the use of an longer bolt. It has been some years ago but I think it was about 2 cm longer or so. I would recommend trying that before reverting to other measures.
Good Luck!

Arno
 
I would fit a threaded insert, eg Helicoil or similar.

There was a thread on here recently about a new type of threaded insert someone had used on a motor bike repair
 
West Coast said:
The bracket which supports the FW pump and alternator on my VP 2003 is secured to the engine block via three M8 bolts. The bolts go into tapped holes in the block, but first go through a housing over the front engine bearing, securing the housing to the engine block in turn.

I had to remove the bracket last season to repair the pump. But, on replacement, I found that thread in the block for one of these bolts has stripped.

Given the block is the far side of the housing, I cannot re tap for a bigger bolt, or put in an insert without removing the housing etc. so, an idea from a wise fellow forumite is to epoxy bond a M8 stud into the block.

Can anyone recommend a suitable product for this, or a company / supplier who can give good advice and a suitable product?
Click to expand...

Any possibility you can drill another 10 mm and tap a new M8 thread????
 
Why not just drill through the housing in order to tap for a larger dia. bolt? Yes, the housing ends up with a bigger hole, and yes, it is a bodge, but I read your question as if you don't want to bother taking it apart and might be happy with quick and dirty.

edit to add:- I haven't had much luck with epoxy in these situations. Probably due to the impossibility of removing all oil etc.
 
Last edited:
Many thanks everyone, some good tips. I had not thought the tapped hole might be deeper, kind of obvious when I think about it. Will check this out this weekend.

Am used to working with epoxies, but more with FRP composites, never had great experiences bonding to metal. All comes down to cleaning and preparation, but this could be difficult to achieve. The one positive thing about epoxy route however is the mechanical fixing I will get to the damaged threads.

Anyway, first thing is to check the depth of hole.........
 
West Coast said:
Many thanks everyone, some good tips. I had not thought the tapped hole might be deeper, kind of obvious when I think about it. Will check this out this weekend.

Am used to working with epoxies, but more with FRP composites, never had great experiences bonding to metal. All comes down to cleaning and preparation, but this could be difficult to achieve. The one positive thing about epoxy route however is the mechanical fixing I will get to the damaged threads.

Anyway, first thing is to check the depth of hole.........
Click to expand...

Most epoxies will soften above 90 degrees C, so not a good selection for the inside of a hot engine.

Good luck and fair winds. :)
 
West Coast said:
Many thanks everyone, some good tips. I had not thought the tapped hole might be deeper, kind of obvious when I think about it. Will check this out this weekend.

Am used to working with epoxies, but more with FRP composites, never had great experiences bonding to metal. All comes down to cleaning and preparation, but this could be difficult to achieve. The one positive thing about epoxy route however is the mechanical fixing I will get to the damaged threads.

Anyway, first thing is to check the depth of hole.........
Click to expand...

If the tapped hole is deeper or made deeper it could be a good idea as suggested by others to insert a stud to full thread depth and secure casing etc with nuts and washers.
 
Gluing engine parts with epoxy has been going on for years. Abraid the area if possible and clean with a pressure pack brake cleaner [watch your eyes] just prior to gluing, especially with aluminium. I used titanium Devcom on my Porsche block about 12 years ago and still looks good. Mate built up the bottom of cylinder wet liner supports in a Ford Diesel boat engine very successfully.
 
superheat6k said:
As you ae using a bolt rather than a stud, there may still be some serviceable thread at the base of the hole, beyond the normal bolt's reach.

I would try using a longer bolt to find out. Full strength is obtained in 1.5 x dia or about 12mm, but even a few turns may be sufficient.

If you do have some decent thread then I would use a high strength locking compound such as Loctite 270, using a piece of threaded studding, and don't overdo it on the final tightening. Use a syringe to squirt the compound into the hole and smother the thread. Wind in the stud to the base of the hole and leave to set for a few hours. Use a nut instead to secure.

Problem with epoxy is the lack of surface area to establish a decent strength bond upon.
Click to expand...

To give some feedback to this thread, checked when on the boat today. Turns out the bolt/thread is standard M8, and yes, the hole is deeper and threaded to its end. Investigations show I have 6mm good thread. Not as much as I would like, but probably OK. So, going for the stud idea, with some locktite.
 
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