big difference between OEM/Aftermarket manifolds

samm835

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Dec 12, 2006
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I am going to purchase new manifolds soon, but there is a considerable price difference between aftermarket and original. Any one have experirence with aftermarket ones being bad? I don't want to spend the time changing and find out they suck
 

Bondo

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Ayuh,..... A few years back I bought a set of GLM manifolds, 'n installed 'em,....
Had hard to start issues right after that,....
Ended up bein' the inner gasket surfaces were 'bout .030" lower than the outer gasket surfaces,...
That didn't allow the proper clampin' forces on the gaskets, which leaked water into my motor,....

Took 'em off, 'n flattened the surface, reinstalled 'em, 'n it's been just fine ever since,....
 

bman440440

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Apr 4, 2011
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I just put a set of GLM's (3 months ago and 75 hours) on mine... before I got them I read some bad reviews... same with other brands as well... mostly what I found was surfaces not being flat... when I got mine I checked all of the surfaces and they where laser straight... I guess there was a problem with them in the past but it seems that they have fixed the problems... I have since helped some friends (2 with 4.3's and 3 with 5.7's) with doing there exhaust and they have purchased the GLM's and all was good with them as well
 

Rick Stephens

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Isn't OEM just whatever happens to be the latest aftermarket production run purchased and marketed as OEM by Merc?
 

JustJason

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It can be a crapshoot sometimes. I just installed a set of Volvo manifolds for the 496 and the surface that mates to the cylinder head was off by .030 to .035.... Which was way thicker than the gasket. Personally what I would do is buy them locally. If you mail order a set and they end up being bad you might have a heck of a time trying to get the vendor to both take them back and also pay for the shipping.
 

alldodge

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I have a doc which came from achris and it gets into aftermarket and OEM and why some risers (exhaust elbows) can cause damage to a motor for reversion. Makes a good read
 

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wahlejim

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I bought some Sierra manifolds on iBoats this year. Checked for flat mating surfaces and make sure you use the gray, thicker gaskets, not the paper stuff. Mine have been fine so far this year.
 

bruceb58

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I have a doc which came from achris and it gets into aftermarket and OEM and why some risers (exhaust elbows) can cause damage to a motor for reversion. Makes a good read
Wow...very interesting.
 

bruceb58

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The marine mechanic that is local to me ONLY installs OEM unless the customer absolutely demands something else. He has found that the OEM ones last longer so the price savings in the long run are not there with aftermarket.

DonS also only used OEM manifolds if that is worth anything to you.
 

Rick Stephens

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The marine mechanic that is local to me ONLY installs OEM unless the customer absolutely demands something else. He has found that the OEM ones last longer so the price savings in the long run are not there with aftermarket.

DonS also only used OEM manifolds if that is worth anything to you.

Not to argue, because I really don't know. I would still ask, how do you define OEM. For instance: If you buy GLM you are purchasing an OEM manifold or riser as Mercruiser has shipped a lot of GLM as the stock manifold. As such, a reseller can publish his GLM manifolds for sale as OEM Mercruiser manifolds. Doesn't seem to me that the OEM tag, when it comes to manifolds anyway, means much.
 

bruceb58

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If you buy GLM you are purchasing an OEM manifold or riser as Mercruiser has shipped a lot of GLM as the stock manifold.
And what proof do you have that that actually happened? Let's just say that GLM had made Mercruiser manifolds at one time...were they to Mercruiser specifications as detailed in the PDF that AllDodge posted or their own?

I used to be an electrical engineer for an auto electronics manufacturer. We made parts for Honda, Mazda, GM and others. When you went to the dealer and bought the OEM part, but our name was not on the part and it was in the Honda, Mazda or GM box.

Unless GLM made the part for Mercruiser and Mercruiser sold it with the Mercruiser part number on it, that would be the only way it is OEM.
 
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cdiamond

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Aug 20, 2008
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this is akin to the debate over tools

craftsman vs snap on

will craftsman do the job ??? of course

are snap on the best ?? of course

are snap on worth the cost ?? thats up to you to decide

same as dino oil vs synthetic oil

will dino oil do the job ??? of course... etc

you get the drift

if you want the best its gonna cost ya - thats just a fact of life
 

Scott Danforth

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BARR and OSCO make castings for Mercruiser, Volvo-Penta, Crusader/PCM, Ilmor and Indmar along withva variety of automotive OEM and aftermarket companies

BARR also makes intake manifolds for a variety of OEMs.

However the OEMs have proprietary casting designs vs the in-house "Will-Fit" marine exhaust manifold casting designs.

Not sure where GLM castings are made as GLM is a will-fit marine company and not a casting house.

Back to comparing OEM to aftermarket Will-Fit. There is a difference in design and finish, however workmanship quality in many cases is the same as the parts come down the same casting lines.

Is the cost difference enough? That is a percieved value. Break down the cost to a cost per year (using the prior mentioned 3 vs 5 year life) and the cost per year is about equal.
 

Bt Doctur

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No mater whose name is on them you should always take a fine flat file to both surfaces to make sure there flat
 
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