WARNING: Brand new OEM Merc manifold casting cracks

[rondds]

Interesting thing happened that I felt would be important to share with other DIYers out there. I was helping my buddy replace the exhaust components on his '95 370DA with 7.4s. All new OEM Merc parts. Got the manifold installed and torqued no problem. In fiddling with the riser blocks and elbows, two of the manifolds cracked during torquing of the top nuts (before we even got to 30 ft-lbs) - one of the four threaded holes on two different manifolds cracked - so out of 16 bolt holes, 2 stripped and cracked the casting. I have to preface the discussion with a disclaimer - Jon has had these elbows and risers off probably 10x for gasket replacement and I had done mine probably 4x, so we are not new to this process. Additionally we used proper torque settings and tightened the bolts evenly and slowly.

SO, fast forward a week later. Back to the marina with two shiny new manifolds (the dealer gave him one gratis as a replacement from Merc, but not both). During the installation, guess what happens? The first one we put on cracks one bolt hole again! Now we're fit to be tied. Before we proceed we take a look at the second new manifold which was still in the box. After closer examination of the manifold and the new bolts that he purchased, we noticed that some of the black paint (e-coating?) ran down into the threads. Also, the bolts come through with the threads pre-coated with some sort of red sealant that is very stiff. So before we F up another manifold, we get the tap and die set out and clean all the threads (bolts and manifolds). After that, everything proceeded as normal with no further problems.

For those of you taking on this job, I'd say it's VERY important to chase ALL the threads, despite the fact that the parts are brand new. We all know that threads need to be chased and bolts need to be cleaned before re-install when replacing gaskets. But new stuff apparently has to be done in the same manner for two reasons...
1. paint and sealant create too much resistance
2. paint and sealant likely give a falsely high torque reading b/c of the gunk that accumulates.


BEWARE!!!

 

[Happy Hour IV]

Changed mine to studs so there is no friction issue on threads in the manifold.

 

[Vince_nj1]

Great post Ron.. Good advice. I never would have thought to clean out the threads on a new install.

 

[rondds]

Vince
Each time I replaced my gaskets over the years I always chased the threads in the manifolds. When I replaced the entire exhaust system on both motors, I used the old bolts. These are not hi torque so there's no worries about using old fasteners that have "fatigued." I don't think I chased the threads on my new manifolds when I did mine so I think the MAIN culprit here is that red crap they put on the threads. It's the same red crap they put on the brass fittings that screw into the manifolds (that handle the water flow). When I did mine 2 yrs ago there was no red stuff - I used teflon tape.

BTW, my 7.4s did not have riser blocks. Just the elbow to manifold junction (no under water exhaust). So I had bolts. Jon has studs that take a nut on the top - common in 'dancers.

 

[Brite Idea]

I've done dozens of manifold and riser jobs and really never had a problem but I would never use teflon tape because it will bind the screw or stud in the hole. I only use either Permatex liquid gasket or plumbers teflon liquid sealer. The advantage of using a liquid is the excess will run out causing no harm, using teflon tape will actually bind the screw or stud and can break the casting as in your case. I will only use a liquid sealer when a bolt enters a water jacket.

 

[rondds]

Brite
Teflon tape was not used on studs. It was used on the brass plumbing fittings (elbows) that screw into the elbows and manifolds and receive the hoses that carry water and coolant to the system. I don't see a need for any sealer on the studs/bolts b/c there is no water passing these fasteners.

 

[Xplicitlnck]

I just did my star motor about a month ago no problems at all. Thank god. But I did use blue locktight. The mechanic at my marina advised me to.. was that a mistake? Yes I know port side to be replaced later this season.

 

[rcknecht]

I did mine this past weekend and used antisieze, on the studs... I torqued the nuts to 25 ft/lbs based on the spec when using antisieze... I had no problems...

 

[floriduramax1]

I did mine this past weekend and used antisieze, on the studs... I torqued the nuts to 25 ft/lbs based on the spec when using antisieze... I had no problems...

Same here. We used anti-seize on all manifold/riser fasteners.

 

[Brite Idea]

Anti-seize or locktite are liquid they are fine. Somewhere in the millions of TSB's from Mercruiser they state do not use teflon tape on fittings or bolts due to expansion that could result in casting failure. I didn't write it I'm just passing it along.
Rob

 

[kkalsch]

Just one more caution.....always check all mating surfaces with a flat file to make sure there true. Last year when I replaced my manifolds there where several spots with tear drops on them from the coating that could of easily caused a leak

 

[rondds]

Anyone use new fasteners or were all the above installs done using the old ones? Could have been a bad batch of castings. For whatever reason, only 2 of 16 cracked.

 

[rcknecht]

I used the old bolts and nuts on my install...

 

[mistercomputerman]

Ron is not an "old nut"...he's a dentist.

 

[rcknecht]

Ron is not an "old nut"...he's a dentist.

Here's a picture of Ron:
[video=youtube;QjW-ajAUFpw]http://www.youtube.com/watch?feature=player_embedded&v=QjW-ajAUFpw[/video]

 

[rondds]

I actually like making toys too.

 

[frankn88]

I just had the same (I think) problem, and came here looking for help. Brand new Merc manifolds, spacers and elbows. Got the biggest vice grips I had and tried to screw those damn studs in, barely made it into the red stuff. When I starting tightening down the whole thing, one popped loose, breaking a chunk of the top of the exhaust manifold in the process! Never thought to get rid of the red stuff considering Merc SENT it that way! Now I have to see if I can get them to send me a new one. Any secrets to getting those studs in all the way???

 

[rondds]

From post #1

For those of you taking on this job, I'd say it's VERY important to chase ALL the threads, despite the fact that the parts are brand new. We all know that threads need to be chased and bolts need to be cleaned before re-install when replacing gaskets. But new stuff apparently has to be done in the same manner for two reasons...
1. paint and sealant create too much resistance
2. paint and sealant likely give a falsely high torque reading b/c of the gunk that accumulates.

 

[frankn88]

Thanks, yes, I saw that. Buying a chaser kit this afternoon. I was talking about actually torquing the thing in with what, vice grips, a pair of nuts?

 

[saopm]

Thanks, yes, I saw that. Buying a chaser kit this afternoon. I was talking about actually torquing the thing in with what, vice grips, a pair of nuts?

Usually a pair of nuts will get you into trouble, but I think in this case it is what the job calls for.