Chrysler 70 & 85 verses 75 & 90

[VivaLaMigra]

Curious about specifications on these pairs of 3-cylinder engines. It seems they started out with a 70 and an 85, then bumped each motor by 5 ponies. The 90 HP had problems, I'm told, with a thin upper ring land and they kept blowing rings. Word is that the dealer "fix" for the problem was to install the 85 hp pistons and rings. Was there an actual power output loss involved there? Now, I know by the time US Marine took the outboard line over there was an 85, no 90. I don't recall whether the lower output 3-banger went back to 70 hp but I suspect it did; I seem to recall seeing a 'gap" in 70 HP model numbers for a few years that was filled by the 75. All these motors had the same bore and stroke, right? Were there porting or compression differences? Carb jetting would clearly be different. What would the diff between the 70 and 75, or a 75 and an 85?

 

[Nordin]

Chrysler brand up until 1984 and then Force from 1985 and until the end in 1999.

Chrysler 70, 75 and 85Hp had same bore and displacement but the difference were in the jets and the porting.
All of them had std. bore 3,312 in, 2,80 stroke and 72,4 cu in displacement.

Later when Force brand, they introduce a 90Hp with 3,375 in bore but same stroke 2,80 in and 75,1 cu in displacement..
This was the same bore as the later 4 cyl. Chrysler 140Hp (150Hp racing model too).
The 120 and 150Hp Force (1990 and up) had 3,375 in bore too but 4 and 5 cylinders instead of 3 cyl for the 90Hp.

These engine had intake ports in the pistons too, soo the port timing was different.

Force also introdce in late 1980:s a 70Hp 3 cyl. engine with only one carb!!!
Whole different engine then the other 70-85Hp engines.

It had 3,375 bore but 2,87 stroke and it had some problems with the design.
The compression was different between the number 1 and 2,3 cyl.
I think it was problem to feed three cylinders equel with only 1 carb.


I am not so familier with these so I do not really know about all the problems, have not worked with one ....yet!

 

[jimmbo]

If the HP numbers dropped in the mid 80s, it might have something to do with going to Prop Rating

 

[Nordin]

Yes, as jimmbo says and I forgot to mention, Chrysler started to rate the Hp at the prop instead of the crank in the late 1970:s.

For example the 105Hp 4 cylinder Chrysler was down rated to 90Hp when rating at prop.

Also forgot to mention in my previous post that there was a 90Hp Chrysler in this 70, 75, 85 and 90Hp range.
The Hp rating of these engines was a mix of jets, porting (timing and size of the ports) and crank vs. prop rating.

All of them had the same bore and stroke.

 

[VivaLaMigra]

I know they all had the same bore and stroke, but the 3-cyl 90 had a top ring that was a rip-off of the OMC "power backed" ring. The land was too thin and they kept popping rings. That engine was only out for a couple of years. My father had the misfortune of having bought one new. He went back to a Chrysler 70. He thought about going with a new OMC but the dealers wouldn't give him anything in trade on a Chrysler 90. The 70 gave good service for quite a while until he ultimately sold that boat. I wasn't aware that Force had bored the motor to get 90 ponies out of it but that makes sense. Also didn't know about power-porting the pistons. Yeah, I knew about the 150 being a 5-banger - stay away - word is they break cranks and throw flywheels like frisbees! But, Bayliner needed a bigger motor so they lengthened the block for a fifth slug. Clearly going with a V6 was too much of a redesign and tooling issue for them.

 

[VivaLaMigra]

Nordin, I know the 3-cyl 70 isn't the greatest outboard around; a friend of mine had one that came on a 17 ft Starcraft CC and it blew up last year. Compression was low on #1 but I got it going with a new trigger. It ran for another few months. When it quit #1 was real bad so I pulled the head and it was detonated. Right now I have a '93 70 HP that has 120 psi in all cylinders and it purrs. How long it'll stay that way is anyone's guess. Motor was laid up for a whole decade - a miracle it didn't seize or at least rust the cylinders. It's on a Bayliner 17 bowrider. Going with one big carb was a cost-cutting move for sure. How well they could balance induction flow to three holes with one carb at all engine loadings is anybody's guess, but if we had to guess, I'd say "Not very!." But, this motor does run and it has power trim, courtesy of the one that blew up last year so somebody witll get a few relatively cheap seasons out of it. But, as for compression on #1 being intentionally lower than the other holes, I'd have to say, "No, not at all, or maybe a couple of pounds at most." My gauge gave same number on all three.

 

[jimmbo]

Chrysler, never Prop Rated their engines, US marine may have started to in the Mid to Late 80s