Power head change for a 1980 V4

spybot

Chief Petty Officer
Joined
Jul 4, 2016
Messages
504
I have the chance of getting a 135 block OMC part number 387750
Will this fit on my lower unit and can i use the internals ie crankshaft pistons, timing ect.
My block is a 1980 V4 85hp part number 0389912 the guy reckons it will fit but dont know if he is just saying that so i will buy it.
I also have the chance of 90hp but dont know the age probably late 80s
Would this be a better choice ?
 

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Pertaining to your 1980 85hp....................

The 1973/74 135hp power-head will NOT interchange... different everything.

The 1980s 90hp power-head would most likely match up to your adapter plate that sits upon the long exhaust housing... same crankshaft, rods, pistons, etc
 

spybot

Chief Petty Officer
Joined
Jul 4, 2016
Messages
504
Thanks for that Joe here are the two blocks hopefully this will help

By block is on the right.
 

Attachments

  • photo283891.jpg
    photo283891.jpg
    152.9 KB · Views: 0
  • photo283892.jpg
    photo283892.jpg
    1.1 MB · Views: 0

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Sorry, that really does nothing for me. However, to eliminate a choice... the 135hp block is of no use to you.
 

spybot

Chief Petty Officer
Joined
Jul 4, 2016
Messages
504
Thanks for that Faztbullet. If i got the crank with it does my fly wheel and end bearings Fit ?
Was it only the main centre bearing that was different ?
Cheers
 

spybot

Chief Petty Officer
Joined
Jul 4, 2016
Messages
504
Just checked and crank main are the same size on both blocks.
My block must be a late 1980 one
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
The 135hp uses a smaller main bearing but you wont gain anything going to the 90hp block as it is a crank rated flat back motor. Its 88hp at prop.
 
Last edited:

spybot

Chief Petty Officer
Joined
Jul 4, 2016
Messages
504
Has the 90 not got the same size ports as the 115 Hp
My 85 was cranked rated i thought after 85 the were prop rated ?
Am i getting everything muddled up ?
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
The 115/110/112/140 have the same porting. The 90s, crank and prop rated are smaller.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
The old pot belly 140hp became the 115hp. The flat back 115hp became the 90hp and 88hp.
 

spybot

Chief Petty Officer
Joined
Jul 4, 2016
Messages
504
So was i correct in thinking that the 90 would have the same ports as the 115 ?
I know it may not have he cut out on the bottom rib to take the potbelly but i can figure how to cut that out.
I was banking on it have the 115 ports
 

spybot

Chief Petty Officer
Joined
Jul 4, 2016
Messages
504
OK so its a case of enlarging the ports on my motor. I have the size of both inlet and exhaust.
I have a drill press but to mill. Is it possible to enlarge these ports by 2 mm using a drill bit?
I don't have access to a mill and dont have the cash to buy a complete bigger engine.
I suppose i will soon see but any advice on this would be good
 
Top