1978 Chrysler 85HP Powerhead Swap

[The Force power]

Thanks.....appreciate the thought. Am in no hurry now that winter is here and the holidays are coming up. Do you know what year models would be compatible for LU swap? It is a one piece with single exhaust.

I'm not sure if the two piece drive-shaft LU can be swapped for an one piece, hopefully the experts will tune in

 

[tg3690]

I'm not sure if the two piece drive-shaft LU can be swapped for an one piece, hopefully the experts will tune in

I'm not sure either.....by just looking at some parts diagrams on marineengine.com......looks like the LU on 85HP 1977-1982 use the same gear case. As well as the 105, 115, and 120HP models in the 1978 year model. Am sure there are others that would work. May try to have my LU repaired instead.....it was still shifting ok and the prop was still turning, although with resistance and making metal. Don't think I will be attempting a LU rebuild myself.....need special tools and know-how.

 

[Nordin]

Topgun and The Force, all 1 piece gear case from I believed 1977-78 when it was introduced up to about 1994 when Mercury started to put their Mercury LU on.
You can put a 2 piece drive shaft LU on, it will fit. The 2 piece drive shaft LU came at Force engines in 1989.
I think there was three different ratios 1:73, 1:93 and 2:1.
If you look for a replacement LU watch out cause there was both 20 in and 25 in LU.
A 25 in 1 piece drive shaft would not fit.

 

[tg3690]

Topgun and The Force, all 1 piece gear case from I believed 1977-78 when it was introduced up to about 1994 when Mercury started to put their Mercury LU on.
You can put a 2 piece drive shaft LU on, it will fit. The 2 piece drive shaft LU came at Force engines in 1989.
I think there was three different ratios 1:73, 1:93 and 2:1.
If you look for a replacement LU watch out cause there was both 20 in and 25 in LU.
A 25 in 1 piece drive shaft would not fit.

Thanks Nordin.....good info.

 

[tg3690]

"If you look for a replacement LU watch out cause there was both 20 in and 25 in LU." Nordin, are you talking about the length of the driveshaft? I haven't dropped the LU yet but plan to do so Wednesday. " I think there was three different ratios 1:73, 1:93 and 2:1." Is the ratio stamped on one of the gears inside or how do you know what the ratio is? Thanks.

 

[Nordin]

Topgun, yes I am talking about the length of the drive shaft.
No there are no stampe or other marks for the ratio.
Best way to check it in my opinion if the LU is not apart is to turn the drive shaft one turn and check how much the prop shaft turn.
If ratio 2:1 the prop shaft turn half a turn when the drive shaft turn one turn.
If the LU is apart just count the tooth at pinion gear and the forward or reverse gear. For example pinion gear 13 tooth and forward gear 26 tooth then the ratio is 2:1 (26 divided to 13).

 

[The Force power]

"If you look for a replacement LU watch out cause there was both 20 in and 25 in LU." Nordin, are you talking about the length of the driveshaft? I haven't dropped the LU yet but plan to do so Wednesday. " I think there was three different ratios 1:73, 1:93 and 2:1." Is the ratio stamped on one of the gears inside or how do you know what the ratio is? Thanks.

I think that is mentioned in my service manual, I'll report back

 

[jerryjerry05]

On the older stuff the gears aren't usually marked(unless your real lucky).
You'll need to count the teeth
Chrysler/Force used different gear ratios on all motors until about 90 or 91
Then they used the same gear sets on everything from 90hp-150hp including the L-drive.

 

[tg3690]

Nordin, Jerry, Force P......thanks for the great responses.

 

[tg3690]

I think that is mentioned in my service manual, I'll report back

Going out to the shop tomorrow.....will check my service manual too.

 

[tg3690]

Nothing in the manual about gear ratios.....did as Nordin suggested....one full turn of the drive shaft moved the prop shaft 1/2 turn....so it seems to be a 2:1 gear ratio. Found a rebuilt LU with one year warranty from Franz's marine. B.O.A.T.

 

[Nordin]

Okey, there you are. Franz Marine is the best source but not the cheapest.
I do not know where you somewhere else can get warranty (but I am in Sweden so I do not know all suppliers in the US), maybe Mastertech Marine.

 

[tg3690]

Okey, there you are. Franz Marine is the best source but not the cheapest.
I do not know where you somewhere else can get warranty (but I am in Sweden so I do not know all suppliers in the US), maybe Mastertech Marine.

Yeah, Franz aint cheap but it is pretty safe buying from him. Mastertech is good too but they didn't have anything. Bill Kelly has his business up for sale and Franz is trying to retire.....guess you could say I am doing my part to help Franz get rid of his inventory. Lol

 

[The Force power]

Found a rebuilt LU with one year warranty from Franz's marine. B.O.A.T.

Just out of curiosity, how much did cost you (trying to compare US vs Canada)

 

[tg3690]

Just out of curiosity, how much did cost you (trying to compare US vs Canada)

B.O.A.T plus shipping.....lol

 

[tg3690]

Now that the holidays are over....getting back to work on this motor. The rebuilt LU is here and getting it ready for mounting. Was looking at a diagram of the water pump housing and noticed a part I don't recall seeing before, and it was not included in any of the water pump kits I have bought before. Is called a "water pump locating disc" part#12-F480388 and item #62 in the diagram. Is it mounted under the water pump seal on top of the housing? Thanks.

 

[jerryjerry05]

It's under the seal, did you remove the seal?
I never saw that either. But I've never removed that seal.

 

[tg3690]

Well, I've never replaced that seal before either so I not sure if it under there or not...but I did buy a replacement seal and was wondering what it was.....thanks. If I get that seal out I will let you know.

 

[tg3690]

It's under the seal, did you remove the seal?
I never saw that either. But I've never removed that seal.

Jerry.....that locating disc is in fact under the water pump seal. It's just a plastic washer. Decided to leave the old seal alone since it looked in good shape, but you can see it in there. Got a new seal and new locating disc and will probably change them the next time I service the pump.