RD-17 crank defects—-

[jethro]

Here is the crank from one the rd-17’s im working on. This is the lower crank surface where the lower main bearing rides.

I can see an area where the center of the needles would have been—- (area with red square arround it)
where it appears that the pins sat stationary and rusted just a tiny bit- leaving an tiny elongated pit about 1/2 the length of the needle.
I am going to try putting the crank in the lathe and clean it up a little with some 400 grit paper. I doubt if this pitted area will change
though- My old phone has pretty bad resolution—–
Do yall think this would eat up the needles ( the tiny pits that is —- ) in operation ? Do the pits ruin the crank for any further use ?

Tim

[20mercman]

I have a friend who is a racer, and he builds two stroke motors all the time at his professional shop. I have followed his advice as he has a lot of experience. Of course, any needle that has pits on it is junk. The crank can be another story. Each one is different. I can’t make out the damage in your photo too well, so what I will offer is that if the pits run in line across the journal, it is most likely not much good as the needles can fall into the groove. If there just a few pits, and they extend no more than 1/4th of the width of the journal, then the needle can bridge over them and not cause a problem. If I had one that had more than one or two small pits that could not be cleaned off with some emery paper, then I look for another crank. The idea here is that the needles will run over the top of a small pits and not cause a problem. The other factor is what is the expected service for the motor you are building. Are you going to run it WOT in Canada for an hour getting to the other side of big water, remote areas, or is just an occasional use motor for a cruise or two a season.

Steve

[jethro]

Thank you 20merc-
My phone is pretty bad a taking pics- not good resolution…..
The pits are more or less scattered all the way round- but they are only about 2 mm at most. I have not yet cleaned it up yet to see how much
it might clear up- but i will need new needles for sure. The needles have very tiny stripes of pitts- about 1/3 of them. so they need
replacing. I looked again at the lower rod to crank- I can "tip" the piston about 3/16 but I really cant feel any slop " IN-LINE" with the rod.
i am wondering if the slop in the flywheel I could feel might have been comming from the mains on the crank. The crank pins look pretty
good. The lower of the 3 mains is the only one showing pitts.
I will try putting it in the lathe and use some abrasive paper on the pitted area and see if it improves any.
Tim

[jethro]

Tried putting it in lathe—- low RPM
worked it with 320, then 400 then 600
That reducesd the area of the defects quite a bit. I think they are over a small enough area now that the (new) rollers might be happy.
I have now noticed that the piston pins are loose in the pistons. – enough that i can see wiggle. As I remember those are supposed
to be snug enough to be lightly driven out. Will try taking out the snap ring and see if they just fall out…..
Maybe new pistons. one is showing some scuffing on the side- and the rings are stuck in the grooves at that same clock position
on the piston. maybe an overheat…

Maybe I can use the crank …… I wont turn down a good one though I f I can find one……
Thanks
Tim

[frankr]

By tipping the pistons, are you saying they have side-to-side slop at the head end? That is quite normal. The pistons have considerable taper. Wrist pin is supposed to be a press fit in the piston at one end, and a slip fit on the other end. The slip fit end should be marked with an "L" or word "Loose" or something. Always press it out through the tight end, and install through the loose end into the tight end. Support the tight end while pressing the pin in and out.

I assume the motor had the lip type seal at the lower end of the crank? That seal was a BIG mistake that destroyed most of them early on. If you do rebuild it, replace the lower bearing with the type that uses a carbon seal, and install a carbon seal assembly. You can find the parts listed under 1956 30hp.

[RICHARD A. WHITE]

quote Jethro:

Tried putting it in lathe—- low RPM
worked it with 320, then 400 then 600
That reducesd the area of the defects quite a bit. I think they are over a small enough area now that the (new) rollers might be happy.
I have now noticed that the piston pins are loose in the pistons. – enough that i can see wiggle. As I remember those are supposed
to be snug enough to be lightly driven out. Will try taking out the snap ring and see if they just fall out…..
Maybe new pistons. one is showing some scuffing on the side- and the rings are stuck in the grooves at that same clock position
on the piston. maybe an overheat…

Maybe I can use the crank …… I wont turn down a good one though I f I can find one……
Thanks
Tim

My only concern would be using the course grit paper, did you mic the journals before and after? I only have ever seen anyone use 2000 grit when cleaning the journals, 320 will remove metal, 2000 not so much, but I am not an expert on motor rebuilding but I am Toolmaker by trade. Check the specs on the sizes of the journals to ensure they are not now too small.

Regards

Richard

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[fisherman6]

I’m not an expert on motor rebuilding either, nor am I a toolmaker but I have a little background in machining and I share the same concern as Richard here. Definitely mic the journals to ensure they are still within spec. I’d be pretty concerned with using anything coarser than 1500 grit, 2000 would be better. You can take a couple thou off a crank journal with 320 with a lathe turning the crank before you know it.
-Ben

OldJohnnyRude on YouTube

[jethro]

I DID notice that the bottom of the crank has a nasty deep trough cut into it where the lip on the oil seal would have been-
I have some Devcon Titaneium filled epoxy– dont know if that would stay in there if I filled the groove —
Does that big groove trash the crank all by its self ???????
I measured the rear section that had the rust pitts…. it is about .001 smaller than the other two. i kind of figured I had nothing
to loose by trying it. I will look in the sealock manual – but it may not tell me …. I would guess it might be like +- .0005 but I am just guessing….
the sealock manual seems pretty vague on some important things……

in the picture- one of the two dark rings on the right end is the deep groove the seal lip made……..

Tim

[fisherman6]

I agree with you on not having anything to lose by trying it. If it’s .001 under the other two it’s probably out of spec considering the other two likely have some trace of wear on them. The are needles though so that wear should be minimal. I too have myou doubts if the Seloc manual will give you the crank journal specs. They try to cover a lot of information in those manuals and give up some specifics for the sake of broad coverage. I’ll bet someone here does have those specs though. I’m thinking you are in the right neighborhood with the +/-.0005. In this case, if that’s all I had and the rest of the journals and throws are good, I’d try filling the groove from the lip seal and running it.

Take care when you finish the sealing surface to make sure it’s flat and smooth. A fine polish is probably not needed but a good finish without grinding marks is needed to prevent premature wear of the seal and leakage. I have never done this on a crankshaft journal myself, but have used lots of lip seals on rotating shafts in industrial machinery applications. Those get super critical, but on a 2-stroke outboard, that’s probably overkill.
-Ben

OldJohnnyRude on YouTube

[jethro]

Thanks everybody for the guidance—
i found on-line someones photobucket page that had a condensed maintenance manual that gave torques and clearances.
The total variation on the mains is .0005 and I am about .001 to .0015 small now. That may be small enough that it could move
enough to bump against the rollers and deform them (not sure how much I can get away with.) I may still try the titanium putty.
I may- as an experiment- try sandblasting the zone just outboard of the rollers but under the seal— to try to make the putty adhere….

I remember that aircraft cylinder barrels are routinely re-chromed on the insides to oversize and then hoaned back down to spec diammeter
so that nominal size rings and pistons can be used. I am wondering if that could be done to a crank ? It is a "hard chrome" process
which does not use soft copper and nickel layers underneath. It is also called "channel chrome" because as it is going on- it naturaly has
a convoluted surface (microscopicly) which tends to hold oil (so I understand). So I suppose it would have to be ground or lapped for a
needle bearing to run on maybe……
perhaps I can do some googleing on that…..

Let you know if I discover anything on that……

Otherwise i will be check with Dan Gano to see if he has cranks…..

Tim

[Author]

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