advice on rebuilding 1989 force 85 powerhead

[BWSmith]

Hi, everyone,

I am thinking about rebuilding the PH on my Froce 85hp. It's currently inoperable due to (that I know of) a blown head gasket and water pump/impeller. As far as I recall, there is no further damage to the engine. I am unaware of when it was last run and how it was running at the time.

I am undertaking this as a winter project. I wish to have the cylinders bored. Would +.040" be pushing it? Or should I try .030? Should I consider the Wiseco forged pistons, or can I get by with the cast ones? I have not opened up the motor, so I'm not sure what I will find. I am interested in maximizing power output without blowing a cylinder wall in the process. I know I should shoot for reliability above all else.

Thank you and I look forward to your responses.

Bryan Smith

 

[roscoe]

Re: advice on rebuilding 1989 force 85 powerhead

?????

Why?

A head gasket and water pump are a Saturday afternoon repair.
Do the fuel pump, and the carbs if you need something to do on Sunday.

Why do a rebuild?
Why bore?

What am I missing?

 

[Scallywag1]

Re: advice on rebuilding 1989 force 85 powerhead

1st off get a manual for this motor. It will help you with whatever you are going to do. Put a new impeller in it, get it to turn over, check compression and for spark. This will let you know if it needs rebuilt and if the electronics are in working order. If you have low compression on two cylinders next to each other it may just need a head gasket.
I just had my 1989 85HP force rebuilt, bored,new pistons,bearings,carbs rebuilt,lower unit gone over, at a cost of $2300. Is it worth putting this much into a 20 year old motor?? It may be better to look for a good running used motor.
You can also find remanufactured powerheads for this motor for around $1500 and core exchange if you have the equiptment (and a manual) to remove the power head.
Hope this helps.

 

[newbie4life]

Re: advice on rebuilding 1989 force 85 powerhead

1st off get a manual for this motor. It will help you with whatever you are going to do. Put a new impeller in it, get it to turn over, check compression and for spark. This will let you know if it needs rebuilt and if the electronics are in working order. If you have low compression on two cylinders next to each other it may just need a head gasket.
I just had my 1989 85HP force rebuilt, bored,new pistons,bearings,carbs rebuilt,lower unit gone over, at a cost of $2300. Is it worth putting this much into a 20 year old motor?? It may be better to look for a good running used motor.
You can also find remanufactured powerheads for this motor for around $1500 and core exchange if you have the equiptment (and a manual) to remove the power head.
Hope this helps.

I concur 100%. I spent $2400 last year to have my power head rebuilt.... then my midleg went out on the drive. I finally decided to break down and part it out. It's a sick feeling having a powerhead with around 10 hours on it that I can't use.

What happens next year when something else goes wrong, and you can't get parts for it?

 

[timdan94]

Re: advice on rebuilding 1989 force 85 powerhead

I know a place that has a whole 85 hp force rebuilt that they want $1500 for

 

[jerryjerry05]

Re: advice on rebuilding 1989 force 85 powerhead

Take the head off and check the cylinder walls for damage.If not to bad then just replace the head gasket.
If you bore it out only go .010 .040 then you will need to re-jet the carbs.Jerry

 

[Frank Acampora]

Re: advice on rebuilding 1989 force 85 powerhead

You have several conflicting statements: You say it has a bad head gasket and water pump but no other damage, then you say you need to re-bore it.

First, pull the head and see the condition of the cylinder liners. If they are fine, then you only need to replace the head gasket and water pump impeller.

If only pistons are damaged, and the cylinder liners are not scored, they can be replaced through the reed openings without dismantling the block.

If the cylinders are scored, then it is time to re-bore. Only go the minimum necessary to clean them up and only do the scored ones. It is not necessary to re-bore all three if only one is damaged. Overbore .010, .020, or .030 as necessary.

Do not bore more than .030 over. Although .040 pistons are available, I have in the past seen recommendations from the factory that no more than a .030 overbore should be done. I suppose this is because of cylinder wall thickness.

Boring usually costs about 65 per cylinder here and WISECO pistons are about 125 complete with small end rod bearing sets. That's direct from Wiseco. I have heard some people have gotten them cheaper on line. Wiseco is definitely the way to go because they are much easier for the average home garage mechanic to install on the rod. Plus, the pistons are forged, not cast, and they sell head gaskets cheaper than stock too.

So, even if you bore all three cylinders, if you do all the other work yourself, then parts for a complete rebuild will cost about 800 bucks.

Now, you also want to increase power. If you do rebuild, before you have the engine bored-out, PORT the bypass and exhaust on each cylinder. Squaring and trumpet shaping the ports will gain you between 5 and 10 horsepower per cylinder on these three cylinder engines. It also gives better low end torque and, believe it or not, slightly better gas mileage at part throttle because of increased engine efficiency. At full throttle you will use more gas because you are making more horsepower. To do this, you need a Dremel and a couple of carbide bits. It is not necessary to re-jet the carbs with port work.

Just be aware that although I port most of my engines, I will not do it for others when I rebuild for them. While I have not yet had any problems related to it, porting does increase the chances of rings catching and major engine damage, thus I do not want to take a chance with other people's engines.

However, it is possible to just trumpet shape the ports and still gain a bit of useable power without any adverse consequences.

If you wish to see an example of porting on a three cylinder Chrysler/Force, go to The Chrysler Crew, join, go to the questions forum and on the left, click on photo albums. look for the album "Frank's Boats."

Boyeson reeds are supposed to give an increase in power but I have never tried them. I have seen them on some engines and was unimpressed by their design and material. They do recommend jets one step richer.

 

[BWSmith]

Re: advice on rebuilding 1989 force 85 powerhead

Thanks, everyone,

I guess "rebuild" was not the best term I could have used to describe what I want to do. I just want to maximize power from the engine. I was attempting to find the Chrysler Crew page as Frank instructed. I was unable to locate it. Tried everything from looking on iboats to google to no avail. I have read of trumpet shaping in several of Frank's posts and am intrigued by it. Could someone please direct me or send me a link so I may see what this looks like? Thanks again.

Bryan

 

[Frank Acampora]

Re: advice on rebuilding 1989 force 85 powerhead

I think I got it attached.

With fluid dynamics, and air is a fluid, a tapered or rounded port on either side of the port will pass more fluid than a straight drilled port.

The factory mills the ports in for ease ond cost of machining. At a minimum, you can round the outside edges of the ports and they will pass more fuel/air mixture.

However, squaring them first, and making the webs between them airfoil shaped, then rounding the bottoms to ease and direct gas flow will significantly improve volumetric efficiency of the engine.

If the photo has attached, it is obvious what I have done. Left side is before and right side is after on the bypass side of the block. Exhaust side is similar. This was, however, my first attempt and the work is a bit irregular. I have improved quite a bit since then.

Do not attempt to port the exhaust side of a 4 cylinder Chrysler/Force. Because of timing and port overlap, you will end up with less horsepower than stock.

Also understand that Chrysler/Force engines are VERY old school. The design is about 50 years old. This type of porting will not gain anything on newer or other type ported engines--for example older Mercs with boost ports or loop charged engines. They have already been maximised. (to a degree)

 

[kandil]

Re: advice on rebuilding 1989 force 85 powerhead

I know a place that has a whole 85 hp force rebuilt that they want $1500 for

Hi I don't mean to high jak the thread but can you please post the # for this place? thanks

 

[Reboot11133]

Re: advice on rebuilding 1989 force 85 powerhead

Frank, could you try to repost the picture. It is just a thumbnail and my eyes are not that good