Inline 6 Exhaust Housing Powerhead Base

[MacGyverJB]

I was wondering if any of you Inline 6 guys could shed some light on my mid-problem. I have 2 different style exhaust housings for an Inline 6. My 150, has a 20" Mid with about a 1.5" thick exhaust divider, with the steering mounts sandwiched between that divider and the mid. It has a pattern that matches the first picture, Gasket 319. Another Mid, this one a 15" also from an Inline 6, has about a 1/4" thick exhaust plate, with the steering mounts housed as a part of the midsection, with 2 clamps. The pattern for this one doesn't match the other mid, but looks more like Gasket #644. (The picture is from a 4 cylinder, but the one I have doesn't have the 2 distinct exhaust ports as my 20" mid.)
My question, to use this 15" Mid, will I have to get an older powerhead like the one that came off this Mid? Ideally, I'd like to put the 150 Powehead onto this mid, but it doesn't even look like I can change the exhaust divider, due to the different thicknesses. Any ideas? Thanks in advance.

[JSK]

Having worked around a number of inlines over the years, a rule that I follow which I learned a long time ago from an old Merc Dealer is never mix Merc parts. Best to go with matching part numbers that correspond to block or plate numbers.

[CKZ]

I think you have aready pretty much figured it out. The gasket with the divider is a late model, 1973 and later. The other gasket is the old model. These were not tuned like the 73 and newer models. The older model is for the 135, 115, 80, on down to the 65 and I think the 125"s. Hope this helps some.

[Mark75H]

The new style (319) starts with the 1972 140 hp

Earlier inline sixes were also tuned, going back to the 76ci 85 hp of 1962; but (as CKZ states) did not have the oversized exhaust chest and separated runners in the tower started in 1972.

There are only 2 bolt patterns for the inline 6's and their close kin 4 cylinders, but many different gasket/base patterns. The bases and gaskets may not interchange between specific models and some years.


There is no way to adapt the new type to the old type, you must have the correct block for the mid. If you must use the mid, 135 is the most powerful powerhead for it. If you do use a 135, make sure you get the base pan for it, it may be critical to mount it if all your other pans are not 135 pans.

[Raceman]

To add a little to what CKZ already said, gasket on left is for 72 1400 and ALL 73 and newer inline 6's (as well as the 4's up until the newer looper stuff) There's no practical way to interchange between the old and new patterns because of the exhaust differences.

[Raceman]

Sam, once again you're quicker with the keyboard.:D

[Mark75H]

Sam, once again you're quicker with the keyboard.

You type a whole lot faster than you did a few years ago!! :D

[Dave S]

Everything stated is TRUE.... Real good advice. I was going to try to use the old style with a newer head, drill a few new holes, weld a new exhaust pattern,and skip a stud. But it ain't worth it the only 2 studs that fit are the front ones, the next 2 back are wider apart..You could get a 135hp block and get close power from it, but do you really need a 15 inch? If your boat had a 15 inch tramsom like a carlson it would make good reason, but on a V with a 20 inch transom just jack it up 5 inches. :cool:

[MacGyverJB]

Thanks for the info guys, that certainly helped! I think I'll be looking for an older 1350 or 1150 powerhead then. I'd like to build up this motor, either as a 15" for my Viper, or for my Glaspar G3, which has a 15" Transom. Either way, it should be a nice looking motor! I was originally considering putting back on the G3 a Mark 78 Mercury, but although I'd love to keep it original, not having neutral or reverse only adds to the challenge of driving it. The more modern inline may be the ticket!

[Raceman]

Just to be sure you know, if you're going looking for an 1150 powerhead you'll need a 70, 71, or 72 ONLY. All the others will have the same bolt pattern problem.

[CKZ]

MacGyverJB,
I don't know if you are looking for a 15" mid for your 1500. If you are there is a 79 inline 80 hp on E-bay. It looks like it is a 15" mid with a spacer plate in it to make it a 20". I am not completely sure this is what it is or whether an 80 hp mid of this year will fit a 1500. If it is and will fit the price doesn't look too bad. You would get a mid and some pistons and maybe some other usefull stuff. I think some of the other guy's will problably know more about this than me. Hopefully they will see this thread and respond. Well I hope it is something you can use. Here's the link http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=50439&item=4536118491&rd=1

[Raceman]

That one will work. How 'bout postin' if you're interested in it. I may bid on it for spare parts if you're not.

[lloyd]

You can make it work weld two places on the back use your newer adaptor plate as guide drill two hole"s worked well in1973 Lloyd"s 8124245785

[MacGyverJB]

CKZ, thanks for finding that one. Unfortunately I contacted the guy on the mariner in Florida and he was reluctant to ship it, so I think I'll be looking for another. Raceman, feel free to bid away on it! I'm still right now in the Inline/V6 debate for my Viper. I have the inline 150 XS if I get a good midsection, or I just got a 15" mid for a V6.... On another note, I'm also restoring a Glaspar G3, and I have a Mark 78 and Mark 75, which I many need to advice on, so I may be grabbing some advice once I pull out those motors. Lloyd, I think the welding might be worth a try, the bolt pattern is the same? Thanks in advance.

[Raceman]

It just won't work that way. The exhaust passages in the 73 and newer (as well as 72 1400 only) blocks are so far out of position in relation to the early housing there's just no practical way to do it. I've seen a later engine stuck on an old BP mid (which is wide open at the top) with an adapter plate, but I just don't see it happening with std. type housings unless somebody's gonna try and gut it completly at the top and re configure it.

I'm not exactly sure what the gasket on the right in the above picture fits, but the earlier 6 cyls had the 2 extra studs (small) at the rear that were left off the later engines.

[Dave S]

That other gasket is a 50 hp, just shown the difference. He problay didn't have a 135 gasket at hand. Race your rite about the last 2 studs, they showed up on the 1968 and up exhaust housings. I think Merc was afraid all the power they were making they needed more studs to get STUCK in salt water. :p