Force 75 Woodruff Key Problems & Lapping Compound Question.

[catsnjags]

I have now sheared 5 woodruff keys. There is no kick or abnormal engine activity when this happens. I have thoroughly read all of the posts in the forum on both the Force and other manufacturers. Learned a lot ! Here's my question: The best advice I have seen relates to cleanup before installing new key. They talk about using LAPPING COMPOUND. I'm game. But I have never used it. Just read some other stuff about it and see that there are several types (Aluminum Oxide, Silicon Carbide, Boron Carbide, etc.) and "grades" (320, 500, 600, 700, etc.) Before I get frustrated with something too weak (or worse, over scoring and creating real problems) which of the experts out there can tell me the type and grade to use? THANKS IN ADVANCE!!

 

[pnwboat]

Re: Force 75 Woodruff Key Problems & Lapping Compound Question.

Your best bet would be to get some "valve grinding compound" at your local NAPA store. It's specifically formulated for metal. I believe it's silicone carbide. Not sure about the grit.

A sheared key can be caused by improperly torqued flywheel nut. If the key way slot on the crankshaft has been damaged/enlarged, you may not be able to prevent it from happening again.

 

[john from md]

Re: Force 75 Woodruff Key Problems & Lapping Compound Question.

As PNW boat told you, the key slot size can cause shearing if it is oversize.

Additionally, if the key slot in the shaft or flywheel has a burr, this will cause a stress riser on the key causing it to fail. Run a piece of cotton over the slots and see if it snags on anything. If it does, dress out the slot with a fine stone or fine cut jewlers file. You can find the files at a Harbor Freight store. Files, Stones and lapping compound can also be found at www.brownells.com.


John

 

[Frank Acampora]

Re: Force 75 Woodruff Key Problems & Lapping Compound Question.

YES, BUT: Are you torqueing the flywheel nut to about 95 foot pounds? You can not do this with a hand wrench--maybe a breaker bar, but not a hand wrench. You can not hold the flywheel by hand. I don't even think a strap wrench will do. You need to put something like a massive screwdriver or a prybar into the teeth of the flywheel and a web on the block to hold it and then tighten the nut.

 

[catsnjags]

Re: Force 75 Woodruff Key Problems & Lapping Compound Question.

Thanks for the advice guys. I pulled the flywheel and worked it over with valve grinding compound and a rag. (It was nasty in there). I can now see that the slot has enlarged in the flywheel. Fortunately, it appears that this part of the flywheel can be punched out and a new one pressed in. I'm taking the flywheel over to a very reputable independent marine repair shop today to get his opinion. The shaft is NOT enlarged (YEA!!) so it looks like I may get this puppy up and running at a relatively low cost.

Again, Thanks. I'll post a followup on the outcome.

 

[john from md]

Re: Force 75 Woodruff Key Problems & Lapping Compound Question.

It may be cheaper to find a used flywheel. They are always on ebay and, if you don't see one listed, ask the various parts sellers if they have one. Many people part out marine engines when they blow a cylinder or lower and the other parts are still good.

John

 

[Frank Acampora]

Re: Force 75 Woodruff Key Problems & Lapping Compound Question.

Don't bother taking it to the machine shop! The flywheel hub is NOT pressed in, but cast in. It can not be pressed out and replaced.The whole flywheel must be replaced.