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88 or 91

mixd

mixd

Contributing Member
"I have two motors one is an 8

"I have two motors one is an 88 force,the other a 91 us marine.They look virtually identical.Should the parts be interchangeble?How much has really changed?"
 
"Mike depends what horsepower.

"Mike depends what horsepower.

Force motors are the most cobbled together outboards in history.

Force was a creation born at Bayliner when they bought out what was left of the bankrupt Chrysler outboard division.

Bayliner was then bought out by Brunswick (who owns Merc), so Force motors kinda come in three flavours:

1) discontinued Chrysler parts
2) a mix of discontinued Chrysler and Merc parts, or
3) discontinued Merc parts

In some model years there was over 50 different models of the same horsepower. As they were rolling down the production line if they ran out of part "x", they would grab something else off the shelf and keep building. If the change was significant enough they gave it a new model number.

So, some parts (if the same horsepower) will swap right out, others may be completely different, it really depends what you have..."
 
"They are both 50hp.I will try

"They are both 50hp.I will try to exchange the lower unit and see what happens.I am also interested in the ignition components,such as the stator cdi components etc."
 
"The 88 and 91 50's shared

"The 88 and 91 50's shared a number of major parts - as you note, most importantly the ignition (blue prestolite) which can be major dollars for components - and they do go bad regularly.

Likewise, the lower units should swap right out.

There were 40 different 1988 models (yes all 50 horse) and 22 versions of the 1991 model.

1991 was the last model year that was based solely on Chrysler parts. In 1992 they switched the model to Merc parts.

So these two motors should be good donor's for one another (mostly)
"
 
"Thanks alot Graham.This very

"Thanks alot Graham.This very good news,ill get to work on this right away.I hear there are a few days of summer left with-out rain.It would be good to go boating."
 
There is at least one more thi

There is at least one more thing bothering me.What is the difference between the old style plugs and the ones without the top pin?Are they interchangable?
 
Not sure what you mean Mike. T

Not sure what you mean Mike. Top pin where? on the end that goes into the cylinder? (surface gap plugs don't have that little metal finger thingy)...
 
"Yeah, ok Graham.I was a littl

"Yeah, ok Graham.I was a little lost for words.I was on my fifth beer.But,yeah, the little thingy.Is there a significant difference between the two types of plugs?"
 
"In general, the surface gap p

"In general, the surface gap plugs (no thingy) are recommended for "sustained higher speed running".

The regular gapped plugs will let her run better if you are doing alot of trolling or running in no-wake zones.

The current listing I have for both those motors is a Champion UL18V surface gap plug as the one recommended for "all round" use and don't see any cross ref to a "gapped" plug.."
 
Thank you very much Mr Graham.

Thank you very much Mr Graham.I will chose my words much more carefully in the future.Just how do these surface gap plugs work?I understand the arc jumping from the electrode in the center to the ground pin(thingy)which ignites the fuel mixture but how does the surface gap plug create the necessary arc?
 
"The arc on a surface gap goes

"The arc on a surface gap goes from the electrode to the closest surface that is grounded when the plug fires (in the case of these, the metal shell of the plug itself - so the closest metal on the bottom of the plug separated from the electrode by the little insulation ring surrounding the electrode - so just arcs back to the base of the threaded part).

The "intended" benefit of surface gap plugs is that they don't have a heat range, never overheat (because none of the plug is extending into the cylinder so they run at the same temperature as the cylinder wall or head itself) which in turn will never cause pre-ignition. A definate plus when running higher speeds and the motor is generating alot of heat that needs to be disappated.

So the gap is (set) by the actual design of the plug itself instead of you having to gap a plug that could otherwise be used on multiple applications at different gaps.

On the downside, a surface gap requires a higher power ignition than a gapped plug to fire properly.

That is why, in general, a gapped plug is recommended for "sustained" lower speed operations, where regardless of whether or not your particular ignition has high and low speed windings (common on Merc's - with only the low speed producing power below about 2500 rpms) or common windings that produce less power at lower rpms, since the ignition my not produce optimum power to correctly fire a surface gap plug.

For myself, on my motors, if I have a cross reference to a "gapped" plug I will run that instead of a surface gap simply because that better suits my style of boating (lower speed the majority of the time), however not every motor has an "optional" plug - could be because the engineers never considered it or because there may be clearance issues that prevent safely running a gapped plug..."
 
"So,for my application,since i

"So,for my application,since i will be doing somefishing and sightseing i should either go to a gapped plug or buy a kicker motor for trolling.Ok that makes sense,thanks Graham."
 
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