Riser flatness

[jimrockireland]

I was inspecting the risers from my 1983 Mercruiser 305/5L MCM228 Serial#6275628. The flatness of the bottom of the riser was a little compromised due to rust on the thin wall separating the exhaust gases from the coolant. I measured it to be about .025 inches deep about 1/5 the length of that wall. Is this serious enough to need a new riser?

 

[Fishermark]

Re: Riser flatness

a little compromised due to rust on the thin wall separating the exhaust gases from the coolant.

In the words of the immortal Clint Eastwood: "Do ya feel lucky?"

I don't know what would constitute an "acceptable" level of compromise... but as you mention the distance between the exhaust and the coolant is very short and a leak there can lead to catastrophic damage. You need a good, flat, sizable amount of metal between the two. If there is any question, then it is time for a new riser and maybe manifold.

 

[MarkSee]

Re: Riser flatness

A few of the seasoned pros here may have a specific spec to go by and will need to respond but there could be some other variables also that come into play.
Here's a couple of articles I had come across and read to try and understand the intricisies of these parts. You may already know this but it helped me:
BoatUS: Seaworthy

Exhaust Risers - Marine Engines : Boats and Yachts Maintenance, Repairs and Troubleshooting :

Mark

 

[jimrockireland]

Re: Riser flatness

Thanks for that article. Quite informative.

 

[Bondo]

Re: Riser flatness

Thanks for that article. Quite informative.

Ayuh,... Post a picture of what ya got,...

The allowable Spec is in the Factory manuals, up in the Adults Only section,...

 

[jimrockireland]

Re: Riser flatness

I'm still working on the posting pictures but I think what I am going to do is get the riser/manifold mating surfaces machined flat. That should fix the flatness issue.