fund razor

You are right.
If this wasn't a cheap, stock boat I would have converted.

jmherbert

I couldn't agree more. Yes, they cost more, but everytime I look at them I am very glad I have them.

I will not own a boat without them now.

Island Time

Fund Razor,

Sorry to hear about the problems. Mine are aluminum look to be in better shape than yours were in. I did not think to check the size because they do look the same...Will put a ruler on them and check. The Mercruisers must be narower than your OMC's cause I had??? more room than you seem to have between the engines. I think the height will be more critical on mine because I am using the Y pipes and not going thru the hull.

Did you get on the water yet?

cloudmaster_321

You shouldn't use stainless bolts on those risers. Stainless is actually a weaker metal than grade 8. Stainless could stretch on you. I originally had stainless in mine, actually broke one bolt tourquing it down, then switched to grade 8, got them from Fastenal.

Wobble

Stainless is fine for the correct torque setting of about 20 ft/lbs.

Stainless is also available in grade 8 even though that is way overkill for this application. Most stainless failures are from not lubing the threads before installation causing the nut to gall when tightened with an air tool.

ljsmith1

Fund,

2 Seasons ago, I went with Osco Manifolds on my stock 1987 Merc Alpha 454. They were thicker than stock (cross-sectional) and seemed well made. They bolted on great, had all of the attachment bosses and came with all the fasteners and fittings.

Last weekend, I went to start up the boat for the season and found I had a stuck #5 exhaust valve. Yes...it was ultimately due to the riser joint leaking internally. When I originally installed these new manifolds, I decided not to use the paper-type Osco riser gaskets supplied, and opted for the Quicksilver grey steelcore gaskets. I used no sealer, filed both surfaces flat, and torqued the riser bolts to 25 ft-lbs. I wonder if I made a mistake on assembly?? (..and guys don't say I bought the wrong type of manifold...I run a stock 330hp and in salt water - aluminum would be a disaster! and stainless would have been a disaster in my wallet!)

Anyway, I am putting it all back together this weekend (with the Quicksilver grey gaskets) and I am going to try the copper gasket spray that McCollins suggested. In addition, I am going to remember to torque those riser bolts a few times in the beginning of this season. Let's see what happens then!

Good Luck!

-Larry

Island Time

ljsmith1,

I actually like the OSCO gasket better than the MC. The same thing happened to mine...MC riser gasket installed by the book leaked and took out exhaust #1. The OSCO gasket I'm using came with a FWC kit. Its thicker and lower durometer than the MC and the ones I got are not made of paper.

cloudmaster_321, the stainless riser bolts should be fine if torqued properly, I used stainless fasteners for everything external on my engines without a problem.

fund razor

Hi IT.

The mercs are a tiny bit narrower, but the stock OMCs were narrower than the repros.
I think that my engines/drives are closer together than some twins I have seen.

I am not thru hull either, I came out to the stock couplers and pipes.

Got the boat in the water Friday. Everything seemed ok and it didn't sink in the slip so I took her out for a real shakedown Saturday. Too many boats out for me to really get a good reading on a new WOT speed, but I was out for about 90 minutes and I think that I have a small gain.

I was seeing 33 mph at 2800 and 52 mph at 4200.
Just a little trimmed out but not trimmed to the moon.

I was having a little trouble with the idle. They didn't want to stay running below 1000 rpms. Passengers would never have know what was up, but the skipper always knows.

I am gonna run out some of this old gas before I start changing things. Good chance that with todays fuels separtating so easily when not kept mixed... could very well be old gas.

fund razor

I am thinking the same thing Mark. The rusted ones that I removed were grade 5. Most broke off.

The torque on these riser to manifold bolts is 14.

Hard to get exact with my needle style T wrench, but I am guessing they are between 15 and 20... hand tightened and triple stepped.

I consulted with a metal guy before I did it.

He said NO WAY use stainless studs for the manifold to block but absolutely ok to use stainless for the risers.

fund razor

I really trust MC. Not only does he know the theory behind every piece of advice he gives... he has actually DONE it. (Over and over.) I went with the copper spray a gasket and coated both sides of the metal crush gasket and both mating sufaces. We shall see what happens.

If he says that the Copper spray a gasket is "magic" then I believe him.

So far so good, but I am gonna check those bolts periodically.

Good luck right back at cha!