Riser Stud Problems Mercruiser 8.1L

[Richard Seccombe]

Hi Everyone,

New to this forum and hope someone out there has experience in this area. I have a 40' Trojan / Carver Express with 2 Mercruiser 472 8.1L engines. I continue to have problems with the riser studs stripping out of the manifold.

The risers appear to be installed correctly and I watched the mechanic torque them to the manual's specs (cold engine). Everything is fine just cruising around, but in both cases they blew out after the boat was running at 3300 to 3500 RPM for an extended period of time.

The riser studs are much smaller in diameter compared to older 454 Mercruisers, and I have heard that Mercury had some sort of recall, but I was also told by the previous owner that an entire set of riser/manifolds were replaced due to this recall.

Has anyone out there had the same experience, and if so, what did you do to correct this. At this point, I'm up for replacing all risers and manifolds with something beefier if there is such an animal.

Any input would be very much appreciated and thanks in advance,
Richard

 

[Haut Medoc]

Re: Riser Stud Problems Mercruiser 8.1L

Welcome to iboats....
I don't have your answer, but it would be helpful if you could post up your year or better yet serial #.....
The studs are stripping or the manifolds themselves?....​

 

[Richard Seccombe]

Re: Riser Stud Problems Mercruiser 8.1L

Hi Haut,

The serial numbers on the engines are OMO 27519 and OMO 27533. I haven't had a chance to pull the latest one apart yet (happened yesterday), but I believe the manifold itself stripped out, not the studs.

My uneducated guess would point to too much torque, or re-torque (possibly loosen) after the engine has warmed up, but there isn't anything in the shop manual that talks about it.

The studs are so much smaller in diameter compared to the older 454's that it really makes you wonder if it isn't a design flaw. I've had riser problems due to age, but never have had them strip out of the manifolds (twice).

Thanks,
Richard

 

[HT32BSX115]

Re: Riser Stud Problems Mercruiser 8.1L

Are these the "Dry Joint" type manifolds?

If they have smaller studs I would bet that they were severely over tightened.

I recently did the manifolds + 3" risers on my 97 454 and I gritted my teeth when I torqued them to specs. If I remember the torque specs it wasn't very much......something like 25 FT-Lbs. I don't know what the dry joint torque specs are but I'll bet they aren't much more and if the studs are smaller they could be even a little less.

A lot of mechanics don't believe low torque specs will do the job so they give it "a little more" just for "mom and the kids"

I'm not saying that this happened but pulled studs are usually the result of over torquing. 25 FT-LBS feels like NOTHING with a 24" torque wrench!
(In fact....by definition it's a 12lb pull with a 24" wrench!)

Hi Haut,

The serial numbers on the engines are OMO 27519 and OMO 27533. I haven't had a chance to pull the latest one apart yet (happened yesterday), but I believe the manifold itself stripped out, not the studs.

My uneducated guess would point to too much torque, or re-torque (possibly loosen) after the engine has warmed up, but there isn't anything in the shop manual that talks about it.

The studs are so much smaller in diameter compared to the older 454's that it really makes you wonder if it isn't a design flaw. I've had riser problems due to age, but never have had them strip out of the manifolds (twice).

Thanks,
Richard

 

[Richard Seccombe]

Re: Riser Stud Problems Mercruiser 8.1L

Thanks for your input. They may have been overtightened although I watched the mechanic do it with the manual in my hand. I read one article that suggested that you shoud re-torque after the engine comes up to operating temperature, but you would think that the manual would take that into consideration when you torque them on a cold block to begin with.

I think the Mercury skimped a bit on both the diameter of the stud and the depth into the soft aluminum manifold.

I guess it's Helicoil time.

Richard

 

[bjcsc]

Re: Riser Stud Problems Mercruiser 8.1L

Richard: I had a problem with the threads stripping out in the transom on both hulls of a Hobie Cat, where the rudders attach. At a local fastener supply store (Warren Fasteners) I found "Keysert" stainless inserts. I used them and they solved the problem and have held up for many years. They're different than a helicoil, in that they're solid and they lock in place. Essentially, you buy the inside diameter the same as what you have, tap the hole to the outside diameter of the insert, screw it in, lock it in with the tool that comes with them (or you may have to request it - mine came with them) and you're done. It's easy in aluminum. I found a place online that has them and they show how they work. Might be something to consider as it is a far better solution than a helicoil...

 

[Richard Seccombe]

Re: Riser Stud Problems Mercruiser 8.1L

Thanks very much for the information. I'll look into them prior to using Helicoils.

Richard