Logo
FULL SITE MENU

1977 Glassmaster Gulfstream 900 ESD

C

Cadmandu

New member
Hi All,
What stern drive do I have on a 1977 250 Cu In inline 6 GM engine?
Is it called a MC-165?
What pitch and size prop?
Thanks
 
Bt Doctur said:
probably a MC-1 , what number is on the prop?
Click to expand...

Thanks for the reply.
I will be picking up the boat this Saturday.
It has a 1977 GM inline 6 250 cu in 165 HP engine.
That is what I thought a MC-1, but after looking an index of the year they started calling them MC-165 after the HP of the engine. But im confused about that info.
The out drive has a lift loop on top.mercruiser_models.gifMC Model Index.jpgster drive id.JPG
 
You might get lucky, but a drive this old should be considered as something you'll probably have to replace. The GM inline six however is one of history's great engines. They still hold their own in today's world in terms of ease of maintenance, smooth operation (you can literally have a full glass of wine placed on it and you won't spill a drop) fuel economy, power. I'ma fan.
 
Cadmandu said:
Thanks for the reply.
I will be picking up the boat this Saturday.
It has a 1977 GM inline 6 250 cu in 165 HP engine.
That is what I thought a MC-1, but after looking an index of the year they started calling them MC-165 after the HP of the engine. But im confused about that info.
The out drive has a lift loop on top.View attachment 25554View attachment 25555View attachment 25556
Click to expand...


if it has the lift ring it’s an mc1 drive , interchangeable with the R, MR, and AlPha One Gen ones.

likelyyou have a 17” or 19” pitch 3 blade black max type prop.

would second that the engines are very reliable for basic maintenance is done. My grandfather had a 150 hp version 1966 ran very well for 30 years, boat rotted around it...
 
Last edited:
Dieter said:
if it has the lift ring it’s an mc1 drive , interchangeable with the R, MR, and AlPha One Gen ones.

likelyyou have a 17” or 19” pitch 3 blade black max type prop.

would second that the engines are very reliable for basic maintenance is done. My grandfather had a 150 hp version 1966 ran very well for 30 years, boat rotted around it...
Click to expand...
Thanks for all the info. What is a R and a MR?
Please see all the repairs that were down to the engine and outdrive.
cant upload pics
 
Of course you can upload pics. Be sure to resize to 800x600 if it is not working. You can resize in any image editing app.
 
According to the drive listings on this site,

a 1977 calls for a 165 outdrive

Based on the year that would most likely be a MC-1 or possibly also called I Drive I forget as its been a long time since I have worked on one that old. It is the predecessor to the R drive which started in 1983. They look almost identical from the outside

The most notable difference between the R and the MC-1 (lower unit) is the vertical shaft, the lower bearing. MC-1 the lower vertical shaft bearing had 13 or 14 needle/Rollers. Also the bearing under the water pump impeller, there is NO lock nut and the outer bearing race sits in housing taper facing UP and the bearing on the vertical shaft the taper is down.

The R/MR/Alpha Vertical shaft lower bearing has 18 needles/rollers.

MR/Alpha, the upper bearing, up sits on top of the shaft bearing which faces up so outer race faces down and has a nut that requires torquing.

MR/Alpha are virtually identical
 
Last edited:
Man I wish I could say that I'm not confused. Thanks for all the great info I will sort it out in my notes and maybe have some more questions. I just pulled my prop and it had 1/4 playin it only 3 pieces came off in front but retaining ring and thrust nut with splines and a counterbore.rhe counter bore kept the prop from getting tight. Is there a piece behind the prop that is missing? The output shaft has about 1/8 " play also is that normal? I'm draining the gear lube now the engine is in neutral should it be forward before I drop the lower outdrive
 
Cadmandu said:
Thanks for all the info. What is a R and a MR?
Please see all the repairs that were down to the engine and outdrive.
cant upload pics
Click to expand...


https://www.perfprotech.com/store/app_themes/ppt/images/tech-specs/alpha-history.pdf

MC1 drives were built from 1967-1982 with some minor revisions - they at times named the drives off the HP of the motor but its an MC1 drive.

The R (1983-1984) and MR (1985) were two versions of drives that fit up to the same bellhousing etc as the MC1 drive but visually look different. There is no eyelt on the top like on MC1 and the R. MR, and later alpha one have a squared off (in the back) cavitation plate vs the round cav plate on an MC1.

1986-1990 the MR was renamed the alpha one.

The good thing is all four of these drives MC1, R, MR, Alpha One Gen one are interchangeable (drive ineternal parts have some differences), so even though your drive is older you can buy a newer gen one drive (or SEI aftermarket replacement) and bolt it in.
 
Cadmandu said:
Man I wish I could say that I'm not confused. Thanks for all the great info I will sort it out in my notes and maybe have some more questions. I just pulled my prop and it had 1/4 playin it only 3 pieces came off in front but retaining ring and thrust nut with splines and a counterbore.rhe counter bore kept the prop from getting tight. Is there a piece behind the prop that is missing? The output shaft has about 1/8 " play also is that normal? I'm draining the gear lube now the engine is in neutral should it be forward before I drop the lower outdrive
Click to expand...
the propshaft will have in an out play, that is normal, but you shouldnt be able to wiggle it side to side.

What should be there on the prop in terms of washers etc depends on if you have the older pressed hub or newer removalble hubs. Figure out how to post a picture and lay it all out on the table .

To remove the drive put it in fwd all the way. this will line up the shifting mehcanism so the drive can slide back with out catching.
 
I only removed the bottom part of the stern drive with the water pump in it. I did it in neutral is that okay?
What is the little spline gear for that is behind the water pump is that what drives it or is it a speedo drive?
How do you think the PO broke off my caviation fins with wood while removing the prop?
Prop Numbers 48-78120-19 it has 15 spline teeth and a L at 9:00 and a K at 6:00
Is it a 19 pitch?
Thanks for all your helpprop off.jpgcrack in lower housing.jpgcavation plate broken.jpg
 
Based on the pic with the crack, and the cavitation plate being broken,That lower unit is done, No good and cannot be repaired or used at all.

So that settles that!

That is a 19 pitch prop, Yes. The other numbers dont mean much for your purposes. Merc props are what they are. the pitch is what is important.
The small splined shaft in front of the water pump impeller is the Shift shaft

MC I lower.jpg




If you can find a replacement Lower unit you may be able to salvage the drive. Otherwise look for a newer complete drive with a ratio as close as possible.

The Ratio for your outdrive should be 1.65:1 for the inline six cylinder 250 (165 hp),

Lower gear case ratio's are typically all the same for small boats such as yours. The gear ratio is controlled by the Upper gear case gear tooth count.
So MC-I or R drive Lower gear case can be used. I don't believe MR or Alpha one lower unit can be used.

If you can find a complete drive with that specific ratio drive that would be great, The next best choice would be a 1.50:1 ratio which was used for V8 engines. Then change prop pitch to get close to proper operating RPM range.


Deiter,



Directly out of the 1977 service manual # 2

MC-1 or I.jpg



The MR and Alpha.

MR's lower unit vertical drive shaft has an O-ring groove just below the splines, A carry over from previous drives. (to keep grease on splines from sliding down the shaft)

Problem was, if you hit something that O-ring groove created a weak spot and the shaft would break at the O-ring groove..............Replaced many broken vertical shafts.

The Alpha One did away with the O-ring groove.
 
Last edited:
Previous owner had a whale tail or doel fin on it - that broke off the cavitation plate.

need a new drive or at least new lower. Is there a thrust hub in front of the prop on the shaft?
 
I bet someone was jumping up and down on it.......or pounding it with a hammer to get the lower separated from the upper
Either way...........Junk!
 
Dieter said:
Doesn’t look to match the part number in the drive drawings here at marine engine

http://www.marineengine.com/parts/mercruiser-stern-drive/index.php

put your drive serial number in will give you correct parts for it ( and engine if use that serial)


ithink it’s shown under the gear case drawing when u get into the drawings fir that drive
Click to expand...

According to the my owners manual the engine s/n is 448445
stern drive s/n is 522399

how does that relate to a MC-1 or a R drive
 
There is one digit missing. Serial number have 7 digits
Please try again

Example

Ratio Serial Number

MC-I

Ratio ..........................Serial number
1.65:1 ...................... 4890460-6268064
 
Thanks Dieter
So do you think it is a MC-1 stern drive only?
I saw on a video that the eye loop at the top is used for clamping a s hook rod to the top of the drive during towing. Like the trailer slip covers that you can put over the hydro cylinders. My bottom drive also has a o ring groove below the splines on the vertical shaft. When i dropped the bottom half of the drive i had it in nuetral is that okay?
thanks again for all your help.
 
Cadmandu said:
Thanks Dieter
So do you think it is a MC-1 stern drive only?
I saw on a video that the eye loop at the top is used for clamping a s hook rod to the top of the drive during towing. Like the trailer slip covers that you can put over the hydro cylinders. My bottom drive also has a o ring groove below the splines on the vertical shaft. When i dropped the bottom half of the drive i had it in nuetral is that okay?
thanks again for all your help.
Click to expand...

yes I do think it’s an MC1 but if you order parts by serial number you can’t go wrong. It seemed like others were disagreeing, they may be right. Bottom line you can replace your beat up lower with an alpha one gen one, you may be better off just buying a complete drive like an SEI vs mixing and matching older uppers and lowers that probably need a reseal anyways.

normally drop the drive halves in fwd. you mentioned the splined shift shaft above. You need to get those two (shift shaft and shift lever) realigned when you put it back together. Also easier if drive is in fwd and you keep pressure on the prop counterclockwise with a bungee cord this keeps it from popping out of gear. You also may need to turn the prop slightly to get the drive shaft aligned with splines in upper unit, can’t do this in neutral.


yes there was a hook to hold up the drive when trailering you can also use a rope off the transom and under cavitation plate. This is only needed if the drive doesn’t stay up. On my grandfathers 1966 penn yan the drive would always drop back down even when new. Hydraulics really never worked right so we’d rope off the drive when on the trailer.
 
I wouldn't bolt an SEI drive to my worst enemy's boat. There are plenty of good used genuine Mercruiser drives on Fleabay and Craigslist for cheap. Also, see if there is a marine used parts/salvage yard person in your area
 
I agree,
My friends drive went south at the end of last season.
Found a very good complete drive on Craigslist for $750. Did impeller kit, pressure checked-passed and new gear oil. Ran it all summer no problems.

There are plenty of R-MR-Alpha drives available online. I would recommend a R drive if you can find one. Not 100% sure an alpha 1 gen 1 will bolt up. input shaft length may be different but not sure.

Buy a good used complete drive as suggested, check it out or have a service place do it for you, bolt it on and hopefully that would be all you need! Try to stay away from drives that were used heavily in salt water.
 
Last edited:
The lower is catastrophically broken and unusable and that would go for what is inside. I would think the insides are no good based on that crack and all the water amd moisture that has seeped in.
Bearings dont like to be exposed to atmosphere, they rust! I would also suggest the upper is in need of a review as the upper bearings and all are most likely shot.

Have you looked at the upper? removed it from the boat? Taken the top cap off and inspected the gears and bearings to see if the are rusted or even frozen?

Dont spend money until you are sure the upper is functional. If it is not then a complete drive will be needed!

If the upper is in good working order and if the lower unit you found is functional then use it as is. The gear ratio is controlled in the upper so most lowers use the exact same gear tooth configuration.
 
Back
Top