Force 50hp with Bigend problems

[Super Dragpack]

Hi all,

We have just upgraded our old (and ultra reliable) Crysler 35hp with a circa '93 Force 50hp.

We ran it for a test today (first time its been run for a year) and it ran VERY well. Good speed and very quiet - but then things changed.

We lost power, the engine became too tight for the starter to turn and the day ended with us stripping the motor down.

We have found that one of the conrod bigends bearings has failed causing damage the rod bigend and the crank.

What we now need to know is, can we find a suitably sized bearing, get the rod repaired/reshaped and the crank machined? Does anyone have the original specs of the Force 50hp bearings and crank etc (i.e. size) so that I can find a slightly oversized bearing to get the crank machined to accept.

Thanks in advance. I normally work on car engines, and mainly classic Mustang hi-po engines - hence the username. Engines I know, 2 strokes . . . well I'm learning.

Mick

 

[Super Dragpack]

Re: Force 50hp with Bigend problems

I have now managed to find the factory specs for the crankpin and the conrod bigend, but I need to know what the tolorence is for the bearing (so I can spec a new size).

So if the crankpin is say 30mm and the conrod is say 36mm, what size should the bearing be? Exact 6mm (2x3mm) or slightly under or over sized to bite?

 

[jerryjerry05]

Re: Force 50hp with Bigend problems

Don't go thru all that(unless you really dig it)work.It's easier to get a smallblock or even a complete motor on Flea-bay.Then just plug and play.J

 

[Super Dragpack]

Re: Force 50hp with Bigend problems

Don't go thru all that(unless you really dig it)work.It's easier to get a smallblock or even a complete motor on Flea-bay.Then just plug and play.J

I don't mind it actually. I spend all my time working on engines anyway since I retired a few years back, so this doesn't worry me. The money does though!!!!

I have decided that one of the conrods is past repairing, so we are after a source for a second hand conrod from any 40-120hp Force/Chrysler outboard.

The piston is marked, but usable.

We have been advised to get the crank welded and reground. Its only .30mm worn, so won't need much. What are your thoughts.

Mick

 

[jerryjerry05]

Re: Force 50hp with Bigend problems

Those kind of parts aren't gonna be easy to get.I'd start looking at any Mercury dealer.They should be able to tell you what's available.
Like I said LOT"S of used stuff on flea-bay.J

 

[pnwboat]

Re: Force 50hp with Bigend problems

The cranks for 2 stroke outboards cannot be ground under size. The surface of the cranks are hardened in order to use the roller bearings. If you grind them, it removes the hardened surface. It's usually cheaper to get a good used crankshaft or purchase a re-manufactured one.

 

[Super Dragpack]

Re: Force 50hp with Bigend problems

The cranks for 2 stroke outboards cannot be ground under size. The surface of the cranks are hardened in order to use the roller bearings. If you grind them, it removes the hardened surface. It's usually cheaper to get a good used crankshaft or purchase a re-manufactured one.

I have heard this a lot about any cranks and other engine internals, and in most cases (with the exception of some modern production engines) this is simply not the case. The old method of hardening a crank is to peen the metal while heating it. This compresses the metal and therefore hardens it. Modern engines are specialy harden coated at high temperatures, something that can be redone, but in most cases - for example Ford Zetec engines - a replacement is a lot cheaper.

Land Rover TD5 heads were some of the first to be hardened which meant they could not be skimmed. But many places now replace the hardened surface after a skim.

I have a couple of sources for experts who can do the work, but am waiting for a price and am still trying to find a usable sensibly priced conrod too.

Thanks for all you help so far though guys - keep it coming!!!!

Mick

 

[Super Dragpack]

Re: Force 50hp with Bigend problems

I can't seem to find anywhere selling (even tried Ebay.com) the parts I need - namely a conrod and maybe even a crank if its cheaper. Anyone got parts kicking around?

 

[Super Dragpack]

Re: Force 50hp with Bigend problems

Does anyone know if a Force 70hp conrod (and piston) is the same as a Force 50hp one. The part numbers are the same, so I assuming 'yes' but would like to check before buying them?

Thanks again

Mick

 

[pnwboat]

Re: Force 50hp with Bigend problems

Connecting rods are the same. Looks like they used two styles of pistons, same diameter (3.375 in. std.). They used both pressed wrist pin and full floating wrist pin pistons.

Here is a good source for re-manufactured crankshafts. I've been running one in my motor for over 3 years now. I done several other motors over the years and have not had any problems with them. Prices are reasonable compared to most places. They also have connecting rods.

http://nwoutboard.com/