Cracked exhaust manifold - Yamaha 4.3L v6

[dangerdj]

Finely cracked on the bottom of the exhaust manifold. Having a heck of a time finding this part online (apparently the Yamaha engines of this kind were made only for a few years). I'm assuming I could use another brand of manifold but wondering which kinds / where to order? Also how much of a hassle is it to put it on if it's not the exact same?

Attached photo is of my engine, link is to part number.

 

[racerone]

I believe they did use GM engines.

 

[dangerdj]

Yes, that's a given - just wondering if anyone has replaced the OEM YAMAHA part with Mercruiser or other manufacturer and how well it mated to the engine block.

 

[Scott Danforth]

first, the exhaust most likely cracked because of improper winterization. hope your motor isnt cracked too

the engine is a GM 4.3, same block and heads as found in a full size half ton truck or a S-10 or Mercruiser or Volvo....

so you can get manifolds for any 4.3 (Mercruiser, Volvo, OMC, etc) however they dont mate very well with the Y-pipe.

there was a complete yamaha 4.3 exhaust swap thread on iboats. do a search. lots of parts have to be swapped.

and no, yamaha was not around for more than a few years. they violated both Mercruiser and Volvo patents and got their hands slapped so...... you have no parts support.

here are a few links

https://forums.iboats.com/forum/eng...765-plumbing-mercruiser-manifolds-on-a-yamaha

https://forums.iboats.com/forum/eng...aha-4-3-v6-exhaust-manifolds-and-engine-block

 

[dangerdj]

first, the exhaust most likely cracked because of improper winterization. hope your motor isnt cracked too

Yeah, I did drain it and flushed with antifreeze but apparently the plugs can get clogged with rust.

the engine is a GM 4.3, same block and heads as found in a full size half ton truck or a S-10 or Mercruiser or Volvo....

so you can get manifolds for any 4.3 (Mercruiser, Volvo, OMC, etc) however they dont mate very well with the Y-pipe.

there was a complete yamaha 4.3 exhaust swap thread on iboats. do a search. lots of parts have to be swapped.

and no, yamaha was not around for more than a few years. they violated both Mercruiser and Volvo patents and got their hands slapped so...... you have no parts support.

Did not know that, thanks for the info. I've talked to three boat mechanics (one of them Yamaha) and none of them have even seen one of these engines! I was naive in thinking that bc it was Yamaha it would be good!

here are a few links

https://forums.iboats.com/forum/eng...765-plumbing-mercruiser-manifolds-on-a-yamaha

https://forums.iboats.com/forum/eng...aha-4-3-v6-exhaust-manifolds-and-engine-block

Thanks, I checked out a few searches but didn't see the first thread. Looks like a lot of work but don't have much choice unless I ghetto the crack with Permatex and drive it into the ground - HA!

 

[Scott Danforth]

you own a boat. maintenance is just part of it.

the issue with a cracked manifold, is it is also cracked on the inside, which will take out your motor

also, do not post in old threads.

 

[dangerdj]

Thanks for the advice! Much appreciated! Have a great day Scott

 

[Antax]

It really wasn't that much work once I figured out the Yamaha coolant flow. I've helped a couple other people swap to Mercruiser manifolds. Biggest part is getting the manifold that will allow the Yamaha risers to bolt up to them. You will most likely need to re-use your Yamaha risers. The Mercruisers I used were about a 1/4" off so I had to use a die grinder and slot them a little.

Like Scott said, don't try to use your old manifolds for 2 reasons, 1. the manifolds are old and if they have already cracked they will continue to crack and 2. they are most likely cracked on the inside. I actually had mine brazed and when I got them back I tested by filing them with water and pressurizing them and they bubbled like crazy. The inside was busted all to pieces. Since the Yamaha recirculates water through the manifolds instead of just using it as a dump they are always completely full of water and partially pressurized.

Hope you haven't given up on them just yet.