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Post by dcdirtrider on May 6, 2024 2:55:45 GMT -5
Hello all, I just finished installing a Motoforce reinforced crankshaft on my SR50 Minarelli. After mating the block halves, I spun the crank and noticed a "wobble" on the stator-side of the crank. There is a smaller wobble on the variator-side as well. I wanted to know if this is gonna be an issue at 11k rpms? The engine spins freely, if that matters... I'm in the US, so parts are either STUPID expensive (relative to Europe), or 3 weeks out for a replacement. I don't have the tools or expertise to "true" the crank, nor do I know who or where can do this work. This scooter has been such a PITA to work on, it may end up as a range-target if it keeps asking for more money. So any advise would be greatly appreciated, for it's sake  I also designed and 3d printed a crankshaft puller, similar to Yamaha's 9089001274. It's essentially a tool that pulls outwards on both sides of the crank to make sure the bearings are seated properly... I think. Will this help at all? |
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Post by aeroxbud on May 6, 2024 3:01:44 GMT -5
I would say that's no good. It will shake its self to bits.
I had a crank way better than that. you could hardly see a wobble, and it just kept eating crank seals.
How did you fit it?
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Post by dcdirtrider on May 6, 2024 3:27:29 GMT -5
Like a professional, or, so I thought. Bearings in the freezer (for a week) and heat on the case... which didn't work. So I used a perfectly-sized socket and rubber mallet to tap on the outer races of the bearings. Heated the bearings with a torch, froze the crank (for a week)... and again, didn't go in. So I put the nut on the end of the crank and wacked it into place with a mallet. Did the same when installing the block-halves except tapping around the case down onto the other half. ALL OF THIS was in a video I watched of a dude working on an Aerox. And after watching more videos from other people, I want to throw some loud-azz crickets into that dude's car because it was so incorrect. Also, none of the videos share the target-temperature for heating the case. So I used about 60-seconds with a propane torch, which was clearly not enough. I just now spent an hour looking for an online service manual, and I found a 1997 Aerox manual that says 150C (?). Now, assuming I f'cked up the install (probable), what's the next move? Find somebody to true the crank? Who the hell does that kind of work? Or buy some dial-indicators, print a crank-truing tool, and start whacking it straight? Or just buy a new crank? I have no idea what to do. I guess I can reinstall the stock crank, since the BBK I'll be using is only an aluminum "sport level" Athena kit. |
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Post by 190mech on May 6, 2024 4:12:51 GMT -5
Crank is bent! NEVER hammer a crank!! They need to be handled very carefully.. Can possibly be trued, lots of vids out there on how to do it..I am a busy man,but can give it a shot if you cannot find someone or be willing to give it a try yourself.. I always heat the cases with a heat gun till the oil starts to smoke (or spit fries) then drop the bearings in.
While the case is still hot.heat the inner race a bit more and drop the crank in..If it sticks, pull it in using the inner race as a support (not the case or outer race)..
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Post by dcdirtrider on May 6, 2024 4:25:38 GMT -5
Crank is bent! NEVER hammer a crank!! They need to be handled very carefully.. Can possibly be trued, lots of vids out there on how to do it..I am a busy man,but can give it a shot if you cannot find someone or be willing to give it a try yourself.. I always heat the cases with a heat gun till the oil starts to smoke (or spit fries) then drop the bearings in. While the case is still hot.heat the inner race a bit more and drop the crank in..If it sticks, pull it in using the inner race as a support (not the case or outer race).. Yep, I just didn't want to warp the entire case. It's happened to me welding steel body panels together, so I was a bit cautious with the heat... which ended up f'cking me more than it helped lol I've seen some of those videos, and there's also a 3d file out there for the crank-rolling tool, but it might still be cheaper to buy a new crank or install the original one for now. Do you know what kind of shops do this "truing" work? Would a general machine shop be the ticket? I live in a state with LOTS of dirt bikes (Colorado), but most motorcycle shops I've found seem to be of the bolt-on work only types  |
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Post by aeroxbud on May 6, 2024 7:49:49 GMT -5
Get a cheap infrared thermometer. They a very cheap and take the guess work out of fitting bearings and cranks.
I guess most motorcycle shops won't true a crank. You probably need an engine builder to do it. I'm guessing that won't be cheap. Probably better off just getting a new crank.I
You are not the only one who wrecked a crank fitting it. I was watching a video the other day of someone hitting the crank web to fit it. 🤦
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Post by dcdirtrider on May 6, 2024 15:49:35 GMT -5
Get a cheap infrared thermometer. They a very cheap and take the guess work out of fitting bearings and cranks. I guess most motorcycle shops won't true a crank. You probably need an engine builder to do it. I'm guessing that won't be cheap. Probably better off just getting a new crank.I You are not the only one who wrecked a crank fitting it. I was watching a video the other day of someone hitting the crank web to fit it. 🤦 Yep, picked one up over the weekend. Not sure it works properly on reflective surfaces (like a bearing), but we'll have to see. Also found a new Athena Racing crank for under $100, so guess that'll be the route I'm going. How is a person supposed to split the crankcase without hammering on the end of the crank? Are there access holes in the block to separate the two halves using a bolt? |
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Post by aeroxbud on May 6, 2024 17:39:43 GMT -5
Get a cheap infrared thermometer. They a very cheap and take the guess work out of fitting bearings and cranks. I guess most motorcycle shops won't true a crank. You probably need an engine builder to do it. I'm guessing that won't be cheap. Probably better off just getting a new crank.I You are not the only one who wrecked a crank fitting it. I was watching a video the other day of someone hitting the crank web to fit it. 🤦 Yep, picked one up over the weekend. Not sure it works properly on reflective surfaces (like a bearing), but we'll have to see. Also found a new Athena Racing crank for under $100, so guess that'll be the route I'm going. How is a person supposed to split the crankcase without hammering on the end of the crank? Are there access holes in the block to separate the two halves using a bolt? I use one of these tools. www.scootertuning.ca/en/crankshafts/39104-crankcase-splitter-separating-tool-buzzetti-4051272154188.html |
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Post by dcdirtrider on May 7, 2024 3:17:10 GMT -5
I've seen these, and their Chinese counterparts on Amazon. From what I can tell, the arms bolt onto the crankcase, and a screw pushes on the end of the crankshaft towards the block? Basically putting constant tension on the crank, rather than whacking the crank with a mallet. If that's how it works, I might just be able to make one in CAD and print it (TLDR explanation lol). But I thought the rule was to not touch the crank with anything at all? I know some Audi and BMW engines have threaded on one side of their engine blocks which are used to split them, I wish they had done that with these engines. |
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Post by 190mech on May 7, 2024 3:39:15 GMT -5
Constant centered pressure is fine, it does side load the main bearings though so they should be replaced when pushing a crank out, again heat helps with that operation also..
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Post by dcdirtrider on May 7, 2024 4:02:26 GMT -5
Constant centered pressure is fine, it does side load the main bearings though so they should be replaced when pushing a crank out, again heat helps with that operation also.. So no instant transfers of energy, got it. Well, I'm 90% done with the printed case-splitter design, it'll be interesting to see if the plastic will hold up, especially on the treads... lol Probably a bit less stress on the tool since the block hasn't been mated together for the last 25 years. Thanks for the help, fellas. Appreciate it! |
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Post by aeroxbud on May 7, 2024 7:09:04 GMT -5
I will be interested to see your case splitter tool in action.
As a rule I would always replace the crank if I split the cases. There has to be a good reason for doing that.
The splitter allows you to split the cases evenly, so you don't damage them.
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Post by dcdirtrider on May 7, 2024 10:29:32 GMT -5
I will be interested to see your case splitter tool in action. As a rule I would always replace the crank if I split the cases. There has to be a good reason for doing that. The splitter allows you to split the cases evenly, so you don't damage them. So far, looks like it'll work. It'll even work for pulling the crank through with a female threaded bolt swapped in. Still no word on whether the plastic will hold up, but it'll be much harder to bend the next crank with this kit.  Is this how your ScooterParts crank tool works? Bolts to the block and screws the crank out? |
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Post by aeroxbud on May 7, 2024 14:55:05 GMT -5
Pretty much. But the position of the bolts can slide and be adjusted for each side.
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Post by 90GTVert on May 7, 2024 22:14:40 GMT -5
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