1979 MCM 260 Impeller Kit Part #'s and Timing Question

[iaboat]

Hello, I'm planning to replace the impeller in my 79 mercruiser 260 with a "pre-alpha" MC-1 drive. I took the boat out the past weekend and temps went up to 190 degrees. I'm going to replace the thermostat while I'm at it since this boat is old and I don't know all of its history. The serial number on the drive is 5462056 and right next to that number it says 1.50R. Does anyone know how I can find out which water pump kit I need? I'm fairly certain it's either sierra #18-3316/3317/or 3319, but I want to make sure. It looks like the main difference is the pump bases.

On an unrelated side note I also replaced the points and am trying to adjust the timing. I have the boat idling at about 650 rpm to check the initial timing, but when I use my light the timing mark isn't holding very steady, it jumps around a degree or two in either direction. Is this normal or an indication of wear in the distributor? maybe the weights? I have replaced the cap, coil, rotor, condenser, and plugs so those are fresh.

 

[alldodge]

Here is your drive
https://www.mercruiserparts.com/260-1978-1982-4898730-thru-6225576

Your pump body is 46-96148T1 which converts to Sierra 18-3116

The pump kit is 46-96148A8 or Sierra 18-3319

 

[iaboat]

Thanks for the help, it is greatly appreciated! I am hoping I can get help with one more thing. I am also replacing the thermostat...but after opening the cover it looks like the previous owner just removed it entirely.

I purchased this kit, sierra 18-3646 but I'm not entirely sure which gaskets I need and what order they are supposed to go on? Here is what I have and my thermostat housing. I believe I only need the gasket for the top cover and the small cork gasket. Seems like the cork should go down first and then the thermostat so it seals but doesn't feel right when I try to set the cover on.

The diagram I have doesn't even show the cork gasket but I'm not sure how it would seal without it. Any ideas how these go on?

This diagram here: https://www.mercruiserparts.com/bam/subassembly/31737/990/70

the the manual seems to contradict that diagram as to what all goes in the assembly, manual shows a sleeve (which I don't have) and the cork gasket.

I attached photos of my housing and the manual, I would really appreciate help on this. I now know why the last person left it out but I want to get it right while I'm at it!

 

[alldodge]

The old drawings are not very good. The thin cork goes in first, then the thermostat, then paper one with the slot on top. Water flow needs to make it past the thermostat (square hole) to keep water in the manifolds. The cooling systems work but most all would be better off converting to newer style thermostat housing.

In the pic on left is your cooling but it doesn't show the water bypassing the stat when stat is closed.

Check out your spring check balls and make sure they are not stuck and are working

 

[iaboat]

OK, so yesterday I tried to install the base from the 18-3319 kit and....the part on the bottom bottom of the base that seals in the bearing is too big, there is no way it will fit. I actually also bought the 18-3317 kit since that is what sierra said would work and I figured I'd return the one I didn't need.

It looks like the base in the 3317 will fit, but it still is different from the original base. The original has two holes/lines coming out of the pump body, whereas the base from 3317 doesn't have either of these. I uploaded pictures, first ones showing the old base, then the next with all the bases next to each other and labeled.

Will the 3317 base work even with the differences or do I need to look for another part? This old mercruiser has been a real pain to get parts for lol, but I still appreciate the help.

 

[alldodge]

Hey Bondo Bt Doctur achris have a look

 

[achris]

You need to confirm you have an MC1 gear housing. As there's no serial numbers on gear housings, you have to do a visual check. Does the gear housing have a 'pre-load' pin on the top of the drive shaft? If yes, you have an MC1 gear housing.

If you have an MC1 gear housing, then you need Merc part 46-57234A1 (I don't use or recommend any aftermarket parts for anything I regard as 'critical'). If your drive shaft doesn't have a preload pin, then it's an MR/Alpha One, and they use part 46-44292A3.

Last thing... Some idiots think that the preload pin needs to be cut off. Check the top of your shaft carefully. If it's got a hole that looks like it would hold a spring, you have an MC1 that someone has cut the pin off :facepalm:...

The other way to check is with the drive shaft bearing (the one under the water pump). With the base out you can look in. If you see the top of a tapered roller bearing, and not much else, then it's an MC1 (and should have the preload pin). If you see a locking collar with 4 cutouts, then it's an MR/Alpha One...

Chris.............

 

[iaboat]

I can see rollers in the bearing and I do have a preload pin (not cut off), so it must be an MC-1. I’ll order that part, and thank you for the info!

Also, I have heard some say to not install a new o ring at the top of the shaft since it falls out anyway. Is this good advice?

Part of the reason for this maintenance is because of an overheating issue (and I just bought the boat this summer so I don’t know it’s full history), and the other part is because the boat left an oil sheen when I brought it out of the water last. I was hoping changing some of these seals would fix it and I’d give it a test this weekend or next.

Do you think this is wise or should I just turn this into a winter project and replace more seals? I couldn’t find signs of leaking oil. The gear oil smelled nasty but I don’t remember it looking milky or having water in it, just lighter colored than used motor oil and it did release some pressure.

 

[iaboat]

Also, looking at the part for the MC-1, 46-57234A1, it seems it doesn’t have the holes in the side that my old base has, is this ok or are those needed for something?

 

[achris]

Also, looking at the part for the MC-1, 46-57234A1, it seems it doesn’t have the holes in the side that my old base has, is this ok or are those needed for something?

If you have a 'flush' hole in the side of the base, then someone has put an earlier MC1 gear housing on. The part number for that base is 46-48948A1... (Check you have a hole in the side of the gear housing with 'FLUSH' cast next to it.)

As for the O ring on the top of the drive shaft yes, omit it. Replacement shafts don't even have the groove for an O ring. I have seen most with the O ring installed hold the shaft seal (in the bottom of the drive shaft housing) open, and allow water in. That results in rusted out splines in the bottom of the driven gear in very short order.

If there's been an overheat, check, very thoroughly, the water pocket cover up in the bottom of the drive shaft housing. It gets hot and distorts, allowing exhaust gasses in and reduces the cooling system efficiency. If there's any signs of leaking, replace the cover and gasket. If there's no signs of a leak, pressure test it... (http://forums.iboats.com/showthread.php?t=556903&p=3825409&viewfull=1#post3825409)

Chris......

 

[iaboat]

I’ll give it a check when I get a chance tomorrow, I suspect it is distorted because when I looked up where the drive shaft installs the other day I remember there was another rubber piece next to it that was pointed off at a strange angle (I believe this was where the water tube goes).

the water tube guide was also melted at the top part and peeling away from the water tube, so im guessing it got pretty toasty.

What worries me is that the impeller didn’t look terribly bad, so im not sure it was the problem. It was starting look a bit dry and cracked but not where it contacted the walls of the housing, so I would think it should still suck in water ok. I was missing the thermostat and heard that can cause problems but idk...

 

[iaboat]

It looks to me like the water pocket cover is deformed, I attached a photo of it. I'm looking at the sierra kit 18-3219, but are there oem parts you'd recommend instead?

I checked the gear housing there are two holes inside just above the bearing, but no "FLUSH" written anywhere I can see, so I'm not sure what to make of it. I also attached a photo of that.

Thanks for your help

 

[iaboat]

I was looking in the wrong place for that port I believe. There is a hole (pictured) and from the research I've done it is a flushing port even though it doesn't have "FLUSH" next to it. How crucial is the part number for these bases? Right now I am planning on installing the 46-57234A1 style base, and I can't find 46-48948A1. Both styles still have holes, just in different locations, so I would think the flushing system would still work but I'd like to make sure.

 

[achris]

No, that's a drain hole, and it needs cleaning out. You can be quite aggressive cleaning that one out too (sometimes you need to be).

If you can't find a flushing port near the water pump base, it doesn't have one, use base # 46-57234A1..

Chris.....