1990 Mercrusier 4.3LX Manifold Bolt sheared when torquing

[ba5e]

Hi All,

I was putting the exhaust manifolds back on the aforementioned motor when the bolt furthest aft broke around half way down the threaded part. The other bolts went in fine but were not torqued up due to me worrying the same would happen. I assume this was due to excessive pressure (a friend was torquing the bolts while I held the manifold in place....wont happen again!!!).

The broken bolt as well as the rest of the bolts does not have any rust/visible damage on them and they were extracted about 6 months ago.

My questions:
1) should I buy a new set or just replace the (possibly) faulty bolt? I've got a quote, and they cost about $4.70 each over here in Sweden for OEM goods.

2) any tips to get the sheared bolt tip out? It is flush with the manifold mounting area.

 

[81 Checkmate]

Re: 1990 Mercrusier 4.3LX Manifold Bolt sheared when torquing

Try using left handed drill bit for extracting the bolt. If it doesnt come out then use an xtractor bit in the hole that you just drilled.
Maybe a little heat too. Safety first!

For piece of mind you could replace all the bolts or just the one and dont let your friend torq them

 

[Bt Doctur]

Re: 1990 Mercrusier 4.3LX Manifold Bolt sheared when torquing

manual shows using 20 Ft.lbs

 

[ba5e]

Re: 1990 Mercrusier 4.3LX Manifold Bolt sheared when torquing

Thanks for the help, with regards to extracting the sheared bolt, I have an access issue...engine #2's manifold blocks access for a drill to get in and I don't want to start taking that one apart....maybe a flexible drill guide of some sort?

 

[81 Checkmate]

Re: 1990 Mercrusier 4.3LX Manifold Bolt sheared when torquing

Can you get a 90 deg head drill in there? Also you can shorten the drill bit.

 

[Bondo]

Re: 1990 Mercrusier 4.3LX Manifold Bolt sheared when torquing

Thanks for the help, with regards to extracting the sheared bolt, I have an access issue...engine #2's manifold blocks access for a drill to get in and I don't want to start taking that one apart....maybe a flexible drill guide of some sort?

Ayuh,.... If ya don't drill that hole, Dead Center, 'n all the way through the broken piece,...

You run a Strong chance of screwin' up the Head...

Do that, 'n yer gonna be pullin' down the whole top end of that motor for repairs, or replacin' that head....

 

[ba5e]

Re: 1990 Mercrusier 4.3LX Manifold Bolt sheared when torquing

I have ordered ? 90 degree drill attachment and will try that. Will return with the results once the tools are delivered.

 

[Silvertip]

Re: 1990 Mercrusier 4.3LX Manifold Bolt sheared when torquing

Any chance that bolt was cross-threaded which is why it broke? Use a bottoming tap to chase the threads and blow out the debris for all the bolts before installing them.

 

[ba5e]

Re: 1990 Mercrusier 4.3LX Manifold Bolt sheared when torquing

Any chance that bolt was cross-threaded which is why it broke? Use a bottoming tap to chase the threads and blow out the debris for all the bolts before installing them.

Good point, could well have been; it was the first bolt in and I may well have been holding the manifold at a slight angle. Now I realise always start in the middle of the manifold, doing the opposite of how you take it off, as it balances the weight a bit better and reduces the risk of these things happening.

 

[MarkSee]

Re: 1990 Mercrusier 4.3LX Manifold Bolt sheared when torquing

Good point, could well have been; it was the first bolt in and I may well have been holding the manifold at a slight angle. Now I realise always start in the middle of the manifold, doing the opposite of how you take it off, as it balances the weight a bit better and reduces the risk of these things happening.

Not sure if you were doing this and though I have not needed to replace an exhaust manifold myself yet, I have read a good tip about finding bolts of the same thread pattern, cutting the top off, then putting those in to help support the weight of the manifold while the proper bolts are installed one at a time. Seems reasonable to me.
Mark