I replaced my Mixer elbow & exhaust extender in my Yanmar 3JH2E. However 2 out of 4 exhaust female

[FriscoRon]

Hi all,
I replaced my Mixer elbow & exhaust extender in my Yanmar 3JH2E. However 2 out of 4 exhaust female treads are stripped in exhaust manifold.

My Question? What is the fix besides re- tapping with a bigger tread tap. Is there another fix besides re-tapping? I am assuming the exhaust manifold is aluminum.

Attached is photos of elbow and exhaust extender attached to exhaust manifold.

Lower right and upper left female threads are stripped inside exhaust manifold.

Any idears on this fix will most appreciative?
Thanks,
Ron

 

[garymalmgren]

There is a rethreading product called Helicoil.
It works
https://shop.advanceautoparts.com/brands/heli-coil
I think you are looking at 8mm thread.
The Advanced auto ad doesn't give a good description of what is in the kit.
But you only need the basics. (coils and inserter)
You can buy a drill and tap to fit and the punch can be anything that does the job.
Here is a youtube of the function.

You have blind holes (or oles as per video) but as long as you have enough room to rotate a tap you can do the repair without removing the manifold.

gary

 

[Gulfisland Fred]

There are inserts available, made of stainless steel, with threads on the outside, so you can drill and tap a bigger hole, screw in the insert, and bolt your original bolts in. I've used them on stripped spark plug holes in aluminum heads.
A machine shop should be able to supply the inserts, or maybe check online.
It's not hard to drill and tap the manifold extender. Get the right size drill. You can often buy the drill and tap as a set. Use red ATF as a cutting oil. Go slow, pull the drill out often to clear the metal chips out. When you tap the threads, go very slow at first, to be sure that your threads are square and straight. Keep the tap lubricated with ATF. Back the tap out often, to get the chips out, and make a clean set of threads.

 

[kloudie1]

The female threads where the studs screw into the manifold? As previously noted, Helicoil is the right answer.. the manifold is most likely a modified cast iron.. Could be an M-6 or an M-8.. verify …
The kits can be purchased at auto parts places or :
https://www.amazon.com/s/ref=nb_sb_ss_i_1_16?url=search-alias=automotive&field-keywords=helicoil+kit+metric&sprefix=helicoil+kits+me,automotive,219&crid=2N7VDD7LFJM9C
EDIT: be sure to verify because this same nut/stud on the GM series engines is M-6.

 

[ice breaker]

Helicoils are the right answer for situations where you want to keep the exact same size thread such as sparkpug holes, but in this situation I feel it would be simpler to just re tap a slightly larger bolt/stud into the manifold. If you use heliecoils you still need to tap larger to get the helicoils in.

 

[Charles Erwin]

M-8 is .315". The drill for 8 x 1.25 coils is 21/64 (.328"). The upsize stud is 10 mm (.394")

The problem with using the next size is these larger studs are too big for the exhaust ell mount holes so you would have to drill those too. And since the nuts/washers for 10 mm are bigger they probably will not clear the casting.

All in all an 8 mm coil is better. They are stainless and removable too which means you don't have to do this again when you wreck the new threads like I would do.

Charles

ps 8mm is also the right size coil for when the fuel filter bleed screw threads strip out of the aluminum canister.

 

[FriscoRon]

thanks gary

 

[FriscoRon]

thanks Fred

 

[FriscoRon]

thanks Kloudie

 

[FriscoRon]

Thanks Ice breaker

 

[kloudie1]

Welcome. Ron

 

[FriscoRon]

thanks Charles

 

[Gulfisland Fred]

thanks Fred

All Good Ron,
I have had a lot of good information and advice from my boat groups. Happy to share the bits and snippets that I know.

 

[FriscoRon]

Thanks everyone,
I bought the Heli-coil kit. size M8 & 1.25 thread size (same has my studs). It was $43 out the door at O'Reilly Auto parts. Looks like a piece of cake. I'm a happy camper. LOL

 

[FriscoRon]

2 stud Heli-coil fix on extended exhaust to Exhaust manifold is successful. However appears there is a 3rd stripped stud. I did a soap test spray. I see foam on top right nut and stud. I know buy experience this nut is not torking like the Heli-coil fix on the other 2 studs. Attached is photo of the foam soap test on 3rd stud and nut. 2nd attachment is videio my new exhaust mixer working good.

 

[Gulfisland Fred]

2 stud Heli-coil fix on extended exhaust to Exhaust manifold is successful. However appears there is a 3rd stripped stud. I did a soap test spray. I see foam on top right nut and stud. I know buy experience this nut is not torking like the Heli-coil fix on the other 2 studs. Attached is photo of the foam soap test on 3rd stud and nut. 2nd attachment is videio my new exhaust mixer working good.

Good work!
Sometimes you get from A to B, only to discover that the road leads on to C. At least now you know how to fix it. How many inserts in the helicoil kit?
Don't be discouraged. You've made progress, tested successfully, and avoided a potential failure at sea. Reward yourself with a libation of your choice.

 

[FriscoRon]

12 heli-coil inserts. More than I need. It came with tap, inserts, and threader. I still needed to buy a T-wrench, and 21/64th drill bit. Total cost of everything. $65.

 

[garymalmgren]

Brass instead of the original steel nuts are a good cheap long term fix.
Also (I am sure you are on top of it, but..), Locktite on the studs into the manifold and anti-sieze on the exposed threads.
Gary

 

[garymalmgren]

Back again.
I just noticed your test photo (congrats on posting good clear shots) that the nuts are stainless.
In that case, forget the brass suggestion.

 

[FriscoRon]

thanks, Gary