Vespa SS180 Crankshaft Problem?
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Molto Verboso
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: 16 Apr 2011
Posts: 1547
Location: Siam
Sun Nov 22, 2020 3:08 am quote
I've put my SS180 motor together with new bearings and new seals. The old crank shaft that was in it was toast. The threads and bearing seats were thrashed. So, I found an original one that looks to be in great shape.

There is problem. When the flywheel and flywheel hub are tightened down on the crankshaft, it will turn freely about half way through the revolution and then the fly wheel rubs badly on the top edge of the aluminum motor case. To me, it appears the crank is not straight. There are no binding issues with the cylinder head and piston.

The SS180 flywheel is two parts, a flywheel and a steel hub bolted in the center of the flywheel. If I remove the flywheel from the steel hub leaving the steel hub in place and rotate it with a ratchet, I can see that the hub oscillates irregularly instead of spinning straight. I have another flywheel and tried it and it's the same problem

Is this an indication that this crankshaft is bent and a serious issue?

My GS160 flywheel is not like this at all. It spins straight, nice and smooth.

The last thing I want to do is get it all done, start it and watch it all get chewed to oblivion before my eyes.

If anyone has any thoughts, I'd appreciate it.
Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1257
Location: Rochester, Minnesota
Sun Nov 22, 2020 6:24 am quote
Sounds like it is bent or the face the flywheel bolts to is off. Guessing bent as it had to of worked at some point. Try this search has a few videos that should help get you pointed in the correct direction.

https://www.google.com/search?q=vespa%20checking%20crankshaft%20run%20out&ie=utf-8&oe=utf-8&client=firefox-b-1-m#sbfbu=1&pi=vespa%20checking%20crankshaft%20run%20out
Molto Verboso
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: 16 Apr 2011
Posts: 1547
Location: Siam
Sun Nov 22, 2020 6:48 am quote
Thank you for the link with the information. Unfortunately, I don't have the equipment or expertise available to do something like that. I'm starting to think that the crank I have is not in-line. I bought it from Peter in Denmark, who is very reliable, but I have a suspicion that the local mechanic who has built my engine "installed" it using a mallet instead of a proper puller, but I can't be sure.

These kinds of things have a bright side. Now I will order a new crank and the right tools from SIP to split the cases, remove the crank, re-install the new one, and learn from it. Next month I have a month off work to do it.
Molto Verboso
Joined: 03 Nov 2011
Posts: 1104
Location: Racing Capital of the World
Sun Nov 22, 2020 7:48 am quote
nomadinsiam wrote:
Thank you for the link with the information. Unfortunately, I don't have the equipment or expertise available to do something like that. I'm starting to think that the crank I have is not in-line. I bought it from Peter in Denmark, who is very reliable, but I have a suspicion that the local mechanic who has built my engine "installed" it using a mallet instead of a proper puller, but I can't be sure.

These kinds of things have a bright side. Now I will order a new crank and the right tools from SIP to split the cases, remove the crank, re-install the new one, and learn from it. Next month I have a month off work to do it.
take it to someone with a lathe and have them chuck it up with a dial indicator; they can measure the run-out for you for probably a drink or something. i suspect it is out of true.
Molto Verboso
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: 16 Apr 2011
Posts: 1547
Location: Siam
Sun Nov 22, 2020 8:10 am quote
Iíll try to find a machine shop to do something with it and keep it as a spare. Itís frustrating when I pay someone I believe to be competent and this happens. Now I have to open the thing up again. I should have just done it myself. Itís getting to a point where Iím not willing to let anyone touch it now as I slowly begin to figure out how to do the things I wasnít capable of before.
Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1257
Location: Rochester, Minnesota
Sun Nov 22, 2020 9:57 am quote
nomadinsiam wrote:
Iíll try to find a machine shop to do something with it and keep it as a spare. Itís frustrating when I pay someone I believe to be competent and this happens. Now I have to open the thing up again. I should have just done it myself. Itís getting to a point where Iím not willing to let anyone touch it now as I slowly begin to figure out how to do the things I wasnít capable of before.
Thereís a lot of things that I wonít let people touch. I find it better to do it myself for the same reasons. Thereís been to many times, Iíve run out of the tools to continue troubleshooting using the tools that I had. Took my car to a garage, to have them replace good parts until they figure out what is wrong and charge a premium for parts and labor. Mechanic tried charging me for hundreds of dollars in parts, I told him those parts were all good I tested them and told you that itís on the work order. Itís the broken wire that you found that was the issue.
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