1983 Mercruiser 5.7 Exhaust Riser Gasket

[RC54]

Pulled my risers to inspect the shutter valves and got what I thought were the correct gaskets to reinstall them, but when I put them on the exhaust manifold the small holes in the gaskets don't line up with the small holes on the manifold.

Did I get the wrong gaskets? If I did can I just punch new holes where they need to be?

 

[alldodge]

No you have the right ones. The small holes are used to restrict some of the water to keep the manifolds full. There large on the items because it makes it easier to sand cast them during manufacture

 

[RC54]

OK, am I missing something here, because logic tells me that since the holes in the gaskets don't line up with the holes in the manifold, then when everything is assembled the holes in the manifold will be completely blocked and nothing will pass through.

Is this the intent? If so, then why even have the holes in the gaskets? I'm referring only to the small round holes. As you can see in the pics the holes in the gaskets are offset from the location of the holes in the manifold.

I'm confused. Wish I had looked at the old gaskets before I scraped them off, but I just assumed that all the holes would line up.

 

[RC54]

I just realized something. Maybe I have the gaskets oriented incorrectly. Should I rotate it 90 degrees? That would make more sense, I think,

 

[alldodge]

This is the correct way for the gasket on the manifold

Just set the riser on top and your good

 

[RC54]

Hmm...OK, that's what I'll do, but I'm still confused about how it's going to work that way.

Thanks for the help!! :thumb: :yo:

 

[alldodge]

If you flip the gasket over the two little holes do line up

 

[rad1026]

this is how mine were oriented.

 

[RC54]

All Dodge, I tried flipping them but it didn't make any difference. The small holes on the manifold are centered, but the holes in the gasket are offset, so it wouldn't matter which way you orient them.

I was just looking at the manifold and I can see rust stains around the surface of the small holes, which leads me to believe that my old gaskets had four rectangle shaped holes. Not like the gaskets that I have now, so now I'm really confused.

 

[alldodge]

I'll take your word for it but they look offset to me.

The gasket on your manifold looks as though the gasket has eroded way over time. In any case the little holes will do nothing to help cool, but they do help get the littl air bubbles out from those sides, which isn't much.

 

[RC54]

The gasket on my manifold is brand new. I just set it on the manifold to illustrate that the small round holes are not over top of the small round holes on the manifold. I had to scrape the old gaskets off of the riser surfaces. It was like they were glued on.

If you don't mind, please take another look at the pic I posted in my first post...the middle pic, and let me know me know what you think about the evidence that my old gasket had four rectangular shaped holes...evident by the rust stains around the small round hole on the manifold. I don't think my old gaskets had these small holes.

I think maybe I'm supposed to have the gaskets like the one in this link...

 

[Bondo]

Ayuh,...... I've never seen a manifold with only 2 tiny holes fore, 'n aft, with slots on each side,.....

Everything I've dealt with had 4 slots, 'n the gaskets formed the necessary restricted holes,.....

 

[alldodge]

Yes I got it now, yours are straight across.
While you could use the gasket in the amazon link, you should use the one you have. The gasket 27-863726 are used with risers extensions. This allows more water to transfer into the riser, then the gasket your using is installed to connect the elbow

Here is the link to your 260 exhaust

http://www.mercruiserparts.com/bam/subassembly/31739/1077/150

 

[RC54]

OK then, this brings me to another question. I've always noticed in the past that I could not place my hand on top of either of the two risers after the engine had been run. It was just too hot, but I've not had any overheating problems either. I've read that on a properly cooling system you should be able to hold your hand on the riser for at least a count of ten. So, if I use the gasket that I have now, which would completely blank off the small round holes on the manifold side, could this possibly cause me to experience overheating issues?

FWIW...that link you posted to the parts breakdown is the exact link I used to find the part number that I needed to order the gaskets that I have. And, I see in the pic that the manifold does have the four large openings, unlike mine with the small round holes. So, that illustration is not representative of what I have, and I've concluded that the gaskets that were previously installed were the 27-863726 type. Not that it matters much as I can't see where the water coming through those small holes would make that much difference in cooling. But, then again, I'm just a novice here.

 

[alldodge]

All things change over time. Merc changed the design of the manifolds, gaskets and other items. What use to be available back in 1983 is no longer available now. Things change due to cost and others because of benefits. The first gen Alpha drive does not move the same amount of water that the Gen 2 does.

Thermostat housings and hose routing's have also changed to help keep things cooler. Do agree most newer designs stay cooler and the older style.

If your cooling system is original, then there is one feed going to the bottom of the manifolds and another line going to the elbows. The elbow feeds have check valves in them. So the mans and elbows get one from to directions and some water is warmer then the other.

The new cooling design has all of the water go in thru the bottom of the mans, then up and out, This design keeps things more even and cooler.

As for the gaskets, I don't see either doing much more then the other. Using the riser extension ones that were installed previously only tells me they may have been original (don't know because it would take more research) but they could also have been replaced before by another

 

[Bt Doctur]

Curious, in post 5 the top pic looks like you forgot to drain the manifold first

 

[RC54]

I completely agree. Since I am the third owner of this boat they definitely could have been changed somewhere prior to my ownership. So, I shall use the gaskets that I have and will surely monitor my temps, at least at first until I am satisfied that there is no change. Which I don't really expect.

Thanks for sticking with me and answering all of my questions. I apologize for being so anal about it. I've been a jet mech for over 40 years and I guess it's just my way of thinking now. As you probably know with jets, we don't leave anything to assumptions. :nono:

 

[RC54]

BT Doctur, you are correct. I did not drain them. Is that a different issue that I should be concerned about?