Merc 888 log style manis and risors?

[Boomyal]

Seems this was a question not too long ago. I just popped of my left risor because my risor to 'Y' boot developed a little pinhole in it while I was winterizing it. I have little clearance around the risor and was unable to loosen it with the dead weight hammer.

Today, I took my modified chisel and was able to pop the risor off the manifold, then pry it up out of the two stepped shaped boot.

The risor used a metal gasket between two gaskets. The metal shim gasket blocked off the water flow, up thru the risor. On the forward water slot. there was a very small hole thru the shim gasket.

I have not taken off the right side yet but why are all the water passages to the risor blocked. The whole mess was packed with sand. The boot was not cooked but had multiple cracks and one that went all the way thru the boot.

I know that the side of the risor, on both, sides is fed with a hose coming back from the thermostat tower. What gives. Why might all this sand have accumulated when I just should have been blown out thru the large water slots that were blocked by the metal shim?

 

[#1colt]

Re: Merc 888 log style manis and risors?

Not sure how much it helps, but i was stumped by your same problem.. The title was 76sea ray srv 195 Help.

Its still posted on page 3.All the info i recieved on there was quite helpful. I was advised by my mecanic not to put pass thru plates in that setup. Because your cooling system will not have proper pressure. And it could cause your circulation pump to cavitate or hot spots in your motor.

The whole idea stumped me as well. Like you when i seperated my manifolds and risers it had a ton of build up in the risers(ontop of the plate). I had only seen those solid plates on closed cooling systems. And they didnt have the pinhole ofcourse.

Best of luck and happy boating.
mike

 

[Boomyal]

Re: Merc 888 log style manis and risors?

When I winterized, I pulled the little brass plug at the back of the risor. They were also packed with sand and until I stuck a little screw driver in the hole, no water came out. Although the all the mating surfaces were in excellent shape and the boot was not fried, I'm sure that they suffered from low water flow thru the risor and boot.

The more I work on this Merc setup, the more I appreciate my OMC stringer drive.

 

[Tail_Gunner]

Re: Merc 888 log style manis and risors?

8)No sand bagging here boom, it's with in month's of a serious can of whoop ass coming your way........

 

[Haut Medoc]

Re: Merc 888 log style manis and risors?

When I winterized, I pulled the little brass plug at the back of the risor. They were also packed with sand and until I stuck a little screw driver in the hole, no water came out. Although the all the mating surfaces were in excellent shape and the boot was not fried, I'm sure that they suffered from low water flow thru the risor and boot.

The more I work on this Merc setup, the more I appreciate my OMC stringer drive.

The sand or blockoff plate has nothing to do with restricting water flow out of the water dumps, in fact it increases pressure out of them so they spray........
I would suspect one of the water dumps was partially clogged at some time, thus causing the boot to fry.....

 

[Boomyal]

Re: Merc 888 log style manis and risors?

Colt, what was the outcome of your issue? Did you have to get new risors?

I had an indepth conversation with my OMC come Black Anchor Guru today. He verified that my blocked risor plates, with the tiny little hole, were correct. But they were not always that way. Merc started to use the blocked plates when they started seeing valve problems that the rapidly changing temperatures in the exhaust manifolds were causing.

The blocked plates keep the manis at a more even temperature and like was said they get their dump flow back from the top lines on the thermostat tower.

The little hole serves two purposes. One it keeps air from getting trapped in the back of the manifold and two, that hole size can be varied to equalize the temperatures on the two manis.

In all events, here is another instance where an infrared thermometer could be your best friend. If one manifold is running hotter than the other, that hole can be enlarged to let more water pass thru it.

It is common to have any sand that enters the system to accumulate on top of the plate. You just want to be sure that the hole behind the little side hex plug is cleared when you winterize.

Interesting, on my '76 888, the mani parts look like they are only a couple of years old. There is literally no corrosion evident. By all powers of observation they are the original ones too. This tends to aggree with my earlier assessment that due to the condition of the paint on the engine and outdrive, this little gem has had very few hours on it in its 29 years.

Inspection of my leaking boot shows no sign of overheating, just cracked in various places due to age. One of the cracks just decided to go all the way thru the boot so I will replace both of them.

 

[#1colt]

Re: Merc 888 log style manis and risors?

Yeah i did end up getting new risers. they were full of scale rust and i figure its just better to replace them at this pointall though the manifolds were in great condition. They must be newer than the risers. Im not sure of the out come yet as the lows tonite here are in the twenties.

I may have explained it wrong but my mechanic said the solid plates were there as haut said to keep adequate pressure.he said if you put pass through thered be a lack of pressure and somtimes a void of water.He said at that point they could start to fill with bubbles of air.

Ill keep your tip in mind about the plug. I took mine to have it winterized theis year (due to lack of time).Maybe it was best. Im tinking the scale rust could have been blocking them up and restricting the flow. hopefully the new risers and circ pump will resolve my issue. when the sun comes back out ill be sure and update.

mike

 

[f_inscreenname]

Re: Merc 888 log style manis and risors?

Now you all got me thinking.

I am in the middle of changing out motors with a motor that used to be closed cooling. It will be raw water now. I do not have room for closed cooling.:'( The manifolds were good but the risers were shot (benefit of closed cooling set up). So I ended up replacing the risers with a set of S/S risers and they sent the gaskets (on the right) below. The closed cooling gasket is on the left. Now I am wondering if I have the right gasket. Research time.

 

[Haut Medoc]

Re: Merc 888 log style manis and risors?

The one on the right looks like the correct one to me.....

 

[Boomyal]

Re: Merc 888 log style manis and risors?

Ditto to Haut's assumption. Without studying the flow diagram, I'm wondering if the dump hose gets any water unless the thermostat is open? If that is the case, you would absolutely need the bleed holes pictured in the right plate.

f'ing, you should post a link to the S/S risors. I'd like to see them.

 

[f_inscreenname]

Re: Merc 888 log style manis and risors?

No link to the site besides eBay but here is a picture.

 

[Hultman]

Re: Merc 888 log style manis and risors?

Interesting thread. I'm in the process of replacing a long block on a 188hp 302 merc from my 1970 Hydrodyne. When taking it apart, I found that one of the exhaust manifolds have the little pin hole plate and the other didn't. I figure this can't be good. Any reason they might have done this other than a simple screw-up?

The old motor had compression all over the board, from 30 to 180 lbs, so I decided not to mess with it and get a long block for it.

Two other questions:

1) Is this what you refer to as a Merc 888? Is that a 302 motor only or does it include the 351's?

2) I would like to convert the motor to through-the-hull exhaust, but can't find a conversion kit. I was thinking of simply drilling pilot holes thorough the hull and in to the Y pipes on both sides. Then boring out the hull and the Y pipe and brazing in a T-arrangement letting the exhaust exit through the hull. Is this a bad idea?

Thanks!

Jim

 

[Boomyal]

Re: Merc 888 log style manis and risors?

Merc 888 is the Merc 1 outdrive with the 188 hp Ford 302 motor. As for your gasket plate situation, my guess is that at one time one or the other was replaced. The story that I got was that they originally did not block the flow from mani thru to the risor. This caused valve problems due to the constant fluctuation of hot and cold water in the manifold. So they restricted the flow to keep the mani's at a constant temp.

So, you either had one original open plate, or someone didn't know any better and figured that water should pass direct. In any event, you would have had one ice cold mani and risor and one warm/hottish one.

As for the thru Hull, I have no experience except that you would want flappers. Also, do an internet search. There should be something out there.

 

[Check77]

Re: Merc 888 log style manis and risors?

New to the forums but I've got a MerC 225 (basically a 888 with different cam/carb) but with the log style manifolds and risers/elbows the metal plate is there to prevent water reversion into the cylinders and has just a steam hole. The hose running from the t-stat housing to the elbow is what actually dumps the the water into the exhaust.

 

[qaztwo]

Re: Merc 888 log style manis and risors?

"the metal plate is there to prevent water reversion into the cylinders"

interesting.

 

[Haut Medoc]

Re: Merc 888 log style manis and risors?

Qaztwo, you have a PM.......​