Confused New Owner of an Old Boat

[Ptr.Torch]

I recently made a non-cash deal for an older boat.
What I think I have is an IMP "Thunder" from 1969.
Sporting an in-line, 165 HP 6 cyl (GMC?) engine
and a Mercruiser Stern Drive.

My book tells me I should be looking at a 250 GMC engine Moldel #160
The Stern Drive tells me its for a 120-140 Hp, Serial #2824078, which has a cracked lower housing.

Did someone replace the Lower unit with one that is undersized, or maybe replaced the 4 cyl with the 6 cyl? And is this mis-match likely the cause for the lower unit being split open?

More to the point, what is going to be the easiest and best way to fix this??

Any info would be appreciated. Just assume I know almost nothing about boats.... (grin).

 

[alldodge]

Welcome

Sporting an in-line, 165 HP 6 cyl (GMC?) engine
and a Mercruiser Stern Drive.

My book tells me I should be looking at a 250 GMC engine Moldel #160

The motor is a 250 cu in inline 6 with 165HP, Merc uses its HP rating

The Stern Drive tells me its for a 120-140 Hp, Serial #2824078, which has a cracked lower housing.

The serial number on the drive can be used on many motors. This LINK shows the 165 with same serial number band

 

[Bondo]

I recently made a non-cash deal for an older boat.
What I think I have is an IMP "Thunder" from 1969.
Sporting an in-line, 165 HP 6 cyl (GMC?) engine
and a Mercruiser Stern Drive.

My book tells me I should be looking at a 250 GMC engine Moldel #160
The Stern Drive tells me its for a 120-140 Hp, Serial #2824078, which has a cracked lower housing.

Did someone replace the Lower unit with one that is undersized, or maybe replaced the 4 cyl with the 6 cyl? And is this mis-match likely the cause for the lower unit being split open?

More to the point, what is going to be the easiest and best way to fix this??

Any info would be appreciated. Just assume I know almost nothing about boats.... (grin).

Ayuh,...... Welcome Aboard,...... Donno whether yer motor or drive was swapped, coulda been either, or both,....
No doubt, you now have a mismatch,.....
The drive coulda worked with that motor, although the gear ratio would be wrong, causing over-reving, 'n lower that expected speeds,.....
That alone, is not the reason for the lower unit failure,..... If the case is split, odds are it had water rather than oil in it, 'n freezing water split the case,....

To move forward, do a compression test on the motor to see if it's worth saving, then get it running,....
If the motor is Ok, you'll need an outdrive with either the 1.65/1, or the 1.84/1 gear ratio, which should run just fine, with the window of prop pitches normally easily available,....
You can run either the MC-1, or the Alpha 1 outdrive, in the ratios noted above,.....
Be forewarned, the yer set-up requires the shorter input shaft on the drive, not the standard longer shaft on many MC-1s, 'n on All of the Alpha 1s,....
Only the GM in-line motors on only the MC-1s uses the shorter in-put shafts,.....
If you end up buying an Alpha 1 drive, you can swap the shorter input shaft from yer MC-1 onto it, so it'll fit properly,....

 

[Ptr.Torch]

Ayuh,...... Welcome Aboard,...... Donno whether yer motor or drive was swapped, coulda been either, or both,....
No doubt, you now have a mismatch,.....
The drive coulda worked with that motor, although the gear ratio would be wrong, causing over-reving, 'n lower that expected speeds,.....
That alone, is not the reason for the lower unit failure,..... If the case is split, odds are it had water rather than oil in it, 'n freezing water split the case,....

To move forward, do a compression test on the motor to see if it's worth saving, then get it running,....
If the motor is Ok, you'll need an outdrive with either the 1.65/1, or the 1.84/1 gear ratio, which should run just fine, with the window of prop pitches normally easily available,....
You can run either the MC-1, or the Alpha 1 outdrive, in the ratios noted above,.....
Be forewarned, the yer set-up requires the shorter input shaft on the drive, not the standard longer shaft on many MC-1s, 'n on All of the Alpha 1s,....
Only the GM in-line motors on only the MC-1s uses the shorter in-put shafts,.....
If you end up buying an Alpha 1 drive, you can swap the shorter input shaft from yer MC-1 onto it, so it'll fit properly,....

::: I have a lot to learn :::
??
Do you think there is any chance of repairing or replacing the lower section ?

 

[Bondo]

Ayuh,.... If the case is split, it's replacement time, not repair time,.....

 

[racerone]

Post pictures of the damaged / cracked housing.----Only way to get accurate opinions on repairs.

 

[Scott06]

Ayuh,.... If the case is split, it's replacement time, not repair time,.....

Yeah probably easier to get a SEI lower

 

[kenny nunez]

If the crack runs parallel to the prop shaft it would not be worth trying to repair it. Get a SEI unit and be finished with it.

 

[redneck joe]

But also check compression and floor condition. Old boat can have rot

 

[Ptr.Torch]

1969 IMP "Thunder" 165HP 20 Ft.
This is the boat. I know I bit off a huge big bite, going from the 10' aluminum to this is... crazy?!
So I started with purchasing the Mercruzer Repair manual.. Now I'm taking stock of what I really have to work with. The manual is of little use here. It is not very helpfull in identify the model and engine.

 

[Ptr.Torch]

I'm told it is 165 HP. I think Im looking at a GMC in-line 6 (250 c.i.?)

 

[racerone]

That is correct.----A GM inline 6 model.------Many ( not all ) had issues with structure under the floor.----Boat appears to have been looked after.

 

[Scott06]

I'm told it is 165 HP. I think Im looking at a GMC in-line 6 (250 c.i.?)

View attachment 404539

Yes it is a Chevy 6. Merc used several sizes over the years ,most common was the 250 cid 165 hp. was also available in earlier 230 cid/150 hp and later taller deck 292 cube models. Very common reliable engine. GM stopped using them in the US in 1982…had the 150 hp version in my grandfathers 1966 Penn Yann. Ran very well for almost 40 years.

biggest thing to look for is transom and stringer rot. Do this before you get too far into it and spend money on parts. The mc 1 outdrive can be bolt in replaced with later R/MR/ alpha gen one drives. The best way to determine exactly what you have is with the mercruiser serial numbers On engine drive and transom. Older boats like this tend to be a mix and match of parts.

 

[kenny nunez]

Try to post a picture of the crack on the gear housing. IMP boats were well built as I had a customer who had one. This being a “sweet water” boat the engine and manifold might be good enough for the time being. Your main issues will be with the drive shift cable system and possible hydraulics. Hopefully the pump in the drive will only be needed to be replaced. The fuel tank might be gummed up however.

To find out which gear ratio drive you have just remove the 4 bolts on the top of the upper gear housing, remove the cover and look at the gears, if they look like both gears are the same tooth count then it is the correct drive. If the input gear looks smaller then it is for either a 120 or a 140 engine. Sometimes serial numbers on the drive can be confusing if at sometime in the past the housings have been changed using original gears. Tooth count will be the most accuarate. All mercruiser lower gear housings were 1.65 to 1 just by conincidence, the ratio was changed in the upper.

 

[kenny nunez]

Try to post a picture of the crack on the gear housing. IMP boats were well built as I had a customer who had one. This being a “sweet water” boat the engine and manifold might be good enough for the time being. Your main issues will be with the drive shift cable system and possible hydraulics. The fuel tank might be gummed up however.
To find out which gear ratio drive you have just remove the 4 bolts on the top of the upper gear housing, remove the cover and look at the gears, if they look like both gears are the same tooth count then it is the correct drive. If the input gear looks smaller then it is for either a 120 or a 140 engine. Sometimes serial numbers on the drive can be confusing if at sometime in the past the housings have been changed using original gears. Tooth count will be the most accuarate. All mercruiser lower gear housings were 1.65 to 1 just by conincidence, the ratio was changed in the upper.

 

[Ptr.Torch]

The drive has two serial numbers. One on the upper/inside, one on the lower/outside.
Inside I see #2825276
Outside I have #2824078

Online parts stores don't go back that far and can't (haven't) found them.

Here I gets confusing to me. What is this? Or more to the point, what should it be? I think I'm looking at a Type 1, Model 160 (?)

 

[Ptr.Torch]

The damage is on the right side, nose of the Lower Unit. I put it in gear (Forward) and it engages. The dog clutch works when turned by hand. Of coarse that means nothing if the specs and clearances are off, it might whine or chatter to beat the band. But I'm thinking there is a chance this crack might be okay to have welded up. Any thoughts?

 

[racerone]

Looks like it had water in it and froze.------Gear housing needs to be replaced.

 

[redneck joe]

Have you read up on finding rot in an old boat? If not, please so so before investing any money or your life before tackling mechanicals

 

[Bondo]

Looks like it had water in it and froze.------Gear housing needs to be replaced.

Ayuh,...... That lower unit is Junk,.....
I suggest you pull the entire drive off, as all that sillyseal says it was probably installed without the gasket,....
'n it'll be easier to determine the gear ratio, manually with it off,....
If it is a 1.98:1, it's not the right ratio for that I-6 motor anyways,....