ST90 help/advice

T

Thumper1500

New Member
I wanted to start a somewhat generic thread that can be used to ask questions without cluttering up the forum with a lot of separate threads. Hopefully this is a good approach and I'll get started with my two immediate questions.

Currently I'm working on fixing up a '73 ST90 and have gotten some excellent advice on several things (I'm a noob to all this). Today I split the cases apart and the gears, surfaces, bearings etc. all look to be in great condition. However, I noticed a piece laying in the bottom of the case that appears to be possibly snapped off of something. Besides the fact that it's concerning that something might be broken, I really don't have a clue what it is. See attached pics - sorry they are out-of-order, the last pic shows it up close - the small, curved, flat piece of metal with the 90 degree tab at the end. Would love to know where this could have come from.

Second, when removing the kick starter mechanism, I noted that there is actually a hole punched through in the bottom of the right side crank case where the spring likely hit against it. In the picture, you can see light through it down at the bottom. I don't know if it's serious or not because 1) it's at the bottom, presumably below the oil line, and 2) all it does is open a hole between the center case and the clutch side, which already has oil in it too. I don't know whether I should do nothing, fill it in with liquid metal or if I need to scrap the right side crank case for some reason.
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Mystery piece.jpg
 
I have no idea what that piece of stray metal in the second picture could be. I'm really scratchin' my head on that and there's no telling through all the years and previous owners what it could be. The closest I can come up with is a chunk from a bearing race???

The engine case picture is a little blurry but it should not have any holes to the outside as you describe the situation and I would not attempt a repair. I did a quick search on Ebay and there are plenty of low cost ST90 engine cases there that are ready for cleaning and rebuild.

I'd scrap that holey engine case.

Rick
 
Is that scrap piece metal? It looks like plastic to me. Steel or aluminum? I'm betting it's just trash, dropped into the dipstick hole.

I think that hole is supposed to be there. It just allows oil to flow from the left side of the engine out to the right/clutch side. So oil isn't trapped in the center cases.
 
Thanks both for the input/replies and sorry for the poor picture quality. The piece of metal is steel and I tend to agree with you - something that got dropped down in there in the past because I can't find anything that remotely looks like that piece. Think I'll ignore it, whistle a tune and carry on :)

As for the case, that hole is jagged, so either not supposed to be there or chipped out more than any original hole, but I don't think it's a problem because there's another hole further back that goes between the cases anyway - look to the far left side down at the bottom, the same level as the hole and you can see light comiing through it too. Obviously the oil should be on both sides anyway. Since the case is in good shape, I'm leaning towards just cleaning everything out (obviously) and using it as is unless anyone thinks that's a big mistake for some reason.
 
Yes, I know exactly what that is - just saw it today again and it's brass and mine's intact. That is about the closest I've seen to the shape tho.
 
I finally figured it out!! When getting around to reassembling my clutch pack, I spotted it. It is a piece that broke off the end of the part closest in the pic below (copied from another thread on the site here).

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Part #38 in this diagram I believe:

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