I have an '87 454 V8 330Hp Alpha 1. Salt water cooled. Had new OSCO manifolds and risers only last 3 seasons before causing trouble at the riser elbow mating surface. I flushed the motor RELIGIOUSLY after every run on the trailer.

No matter what gaskets I used (steel or fiber), and proper torque (& regular re-torquing) of the riser bolts, the damn thing still let water in, and rusted my exhaust valves over the winter. End result - bent pushrods and stuck valves.

Heads are going out tomorrow to have a valve job. Need to start ordering parts tomorrow.

I read that OSCO are POS. What about Barr, or GLM? The Merc stock manifolds with the ceramic coating look nice, but at $400+ ea. I am skeptical that they will only last as long as the aftermarket (GLM are $200 ea w/ galvanized coating). Keep in mind that I am typically on Long Island Sound...

I am keeping this motor bone stock for now because I am not sure how much longer I am going to keep the boat, but want to get at least one more good season out of it (maybe 2).

find something with a dry joint.

I've read good reports abou the GLM manifolds. They have a good solid machined mating surface and the jackets are well spaced. The general cause of leaks though would be the risers though, not the manifold. The riser flange for a stock riser / elbow is a beast to hold square. You should look at some free flowing aftermarket risers which will cause less water restriction and lower the out going water pressure to allieviate pushing past the gaskets.

For my money, I'd go with the GLM to replace the manifolds as a start though, then find some good fitting risers to match to seal it all up as best as possible.

Good luck!

STAY AWAY FROM THE CHINA CRAP FROM GLM. Osco is normally a very good replacement manifold. You must have gotten a bad pair. Try Barr this time and use the silver gasket.

Yoy can buy Merc oem ceramic coated manifolds for $278 + shipping from boatfix.com

At the time in early 2005, I had already purchased the OSCO manifolds when a few folks from here PM'd me to tell me I made a big mistake. They said that they were crap. After the first season I took the risers off and saw that they were already seeping. I used the silver gaskets with the SS core. Everything was torqued per spec. After running in 2006, I didn't take them off and winterized the boat. In 2007, I was shocked to have one stuck exhaust valve on the port side. Upon disassembly of the manifold and valver cover, my valve was stuck open and a pushrod was bent. I was able to free it without taking the head off. I replaced both riser gaskets again (after checking all surfaces for flatness and using NO sealer with the silver gaskets) and I ran the rest of the season, and put her to bed again w/o taking the risers off again.

She sat for 2008 and I am now getting her ready for 2009 and I find all of this BS...

This is not a high perf application, and I really don't want to spend mucho $$$ for dryjoint or other major upgrades. I just want to get 2 more good seasons out of her before I sell her to someone else to repower.

I want to find a manifold that can hold up to Salt Water and won't leak at the stock riser interface...

I do several manifold replacements every year(on cust. boats). Knock on wood, I have never had a pre-mature call back due to a failure or a leak. My suppliers stock GLM, OSCO, and BARR. I will use OSCO and Barr only. I have seen the GLM's returned for warranty claims from other mechanics and have seen water jackets plugged from the factory and in one case seen an exhaust port plugged (with slag). When I do my installs I always use the silver gaskets. I also scrap the factory primer coating off the gasket surface and then I take a sanding block and 80gt. and ensure a perfect gasket mateing surface on both manifold and riser. Lately I have even been adding a light coat of black RTVon each side of the gasket (even though the instructions say to use nothing).

Sorry to hear about the problems. I too have used a number of OSCO manifolds on different boats over the years. Never had a problem with any of them.



Darrell.

Osco Manifolds are half the internal thickness of any OEM manifold, that is where the cost savings is. They will last half as long and disipate the heat half as well. Always keep in mind you get what you pay for. They will not back any warranty claim presented either. If your lucky the dealer you purchase them from may stand behind them.