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Post by chrisg on Apr 13, 2020 11:48:47 GMT 1
Hi, My 4L0 crank has slipped. Took me a while to come to the conclusion. It wasn't running on the RH pot. I swapped ht leads, cleaned carb numerous times, checked exhaust, new plug; you name it , I tried it. However when I "timed" the bike on the RH pot (normally its timed on the LH pot with a dti) the bike runs fine on the RH pot but not the LH.  My first thought was to get the crank re-built, but I'm concerned that this can happed again. I understand that back in the day, production racers used the aircooled crank inner webs to prevent slipping as they are splined. Is there any other way of preventing this in the future? Any thoughts welcome. Thanks |
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Post by muttsnuts on Apr 13, 2020 12:02:27 GMT 1
weld the crank pins after rebuild
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Post by 4l04ever on Apr 13, 2020 13:12:24 GMT 1
You can verify your findings by marking TDC for left and right cylinders on your flywheel, then measure round the flywheel from one mark to the other both ways round. If the measurements are different, then your crank is not at 180 degrees anymore.
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Post by chrisg on Apr 13, 2020 14:14:54 GMT 1
weld the crank pins after rebuild Will this hold. I'm worried it may crack, due to the heat affected zone. Would loktite do the job ? |
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Post by steven on Apr 13, 2020 14:20:13 GMT 1
...as above, or you can use two DTI,s , one down each plug hole.
Did it slip in use ? or has somone been over zealous when tightening up prim drive nut / alternator rotor ? etc ?
Paul at PJME told me there is more chance of it slipping/moving if the crank has been rebuilt a few times.
Paul said after being pressed in and out a few times, you loose a bit of the interferance fit.
Did I not read somewhere, that some places wont touch a crank that has been welded up ?
Steven.
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Post by chrisg on Apr 13, 2020 14:24:31 GMT 1
I purchased the bike like this, however I did get the bike cheap and with the intention of completing a full resto.
Is this a Achilles heel of the LC range ?
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Post by steven on Apr 13, 2020 15:54:41 GMT 1
Hi Chris, No, I would say it is just something to be aware of. As far as loctite goes, im not a big fan of "glue" ... it does have its uses, but as I said, im no big fan. I have seen LOADS of folk using loctite, thinking it will be a wonder cure. Lots of people just slap it on greasy/oily threads etc and think "jobs a good un." To use loctite properly, you should de-grease all threads before use.... and the first thing I say to people when they use loctite is......"what do the numbers on the arse of the bottle say?" Loctite has a shelf life, and the date is usualy on the bottle somewhere, usualy the arse end of the bottle. Lots of people get a bottle of loctite and keep it for years as it doesnt get used too much at home, which then usualy puts the shelf life out of date. I wouldnt use out of date stuff on Elsie, she deserves better than that ! :-) Mr Brunel never used it once ! :-) en.wikipedia.org/wiki/Isambard_Kingdom_BrunelSteven. wdarc.org/Loctite%20Guide.pdf |
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Post by chrisg on Apr 13, 2020 18:43:56 GMT 1
Hi Chris, No, I would say it is just something to be aware of. As far as loctite goes, im not a big fan of "glue" ... it does have its uses, but as I said, im no big fan. I have seen LOADS of folk using loctite, thinking it will be a wonder cure. Lots of people just slap it on greasy/oily threads etc and think "jobs a good un." To use loctite properly, you should de-grease all threads before use.... and the first thing I say to people when they use loctite is......"what do the numbers on the arse of the bottle say?" Loctite has a shelf life, and the date is usualy on the bottle somewhere, usualy the arse end of the bottle. Lots of people get a bottle of loctite and keep it for years as it doesnt get used too much at home, which then usualy puts the shelf life out of date. I wouldnt use out of date stuff on Elsie, she deserves better than that ! :-) Mr Brunel never used it once ! :-) en.wikipedia.org/wiki/Isambard_Kingdom_BrunelSteven. wdarc.org/Loctite%20Guide.pdf I have been in contact with Martin at Taymar and I'm thinking of getting the inner webs from an A/C bike and getting him to make a Hybrid crank. I'm not a big fan of loktite, however I have been to factories where they "glue" cars and even aeroplanes together, so it does have its uses. |
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Post by dougw on Apr 21, 2020 9:38:38 GMT 1
It was never a big problem back in the 80`s when I used to ride LC`s on the road and race them.
Things might be different now , as mentioned the cranks may have been apart a few times.
I spread an LC crank after some pretty horrific overrevving of the poor thing racing at Three Sisters , seeing if it still misfired at stupid revs ( It did , I just broke it, misfire traced to loose connection on ignition pulse coil)
Terry Shepherd rebuilt the crank and tack welded the crank pins, also supplied some straight cut primaries, apparently kinder to cranks when being abused by oafs.
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Post by chrisg on Apr 21, 2020 18:20:48 GMT 1
The bikes 40+ years so anything could have gone on. It may have even been a track but, who knows. I just want to make it reliable and useable. |
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Post by Tobyjugs on Apr 21, 2020 20:12:33 GMT 1
Ive had two crank problems.
One cranked had slipped and was out of phase, the other just started to spread. The slipped crank i just adjusted and spot welded, that one is in my 400cc YPVS block with pinned valves. The other was rebuilt with new bearings etc and spot welded.
These sort of repairs might not be for every one, but i just think if i can get another life out of them before they are scrapped i will do it. Its all about weighing up the pros and cons and what are you prepared for. It could be a short service life.
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Post by bare on Apr 22, 2020 19:06:15 GMT 1
Just weld it. There are only a finite # of times that a crank can be pressed.. 3 times 'maybe' on an OEM crank ..
.. before the friction fits become unreliable.
A decent welder can make it redo able .. one more time
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Post by Tobyjugs on Apr 24, 2020 7:55:03 GMT 1
I would Just like to add it's not just a question of welding it. It has to be held down in the correct fashion. When you weld it the area that is welded will shrink a very tiny amount and this will cause it to deform slightly, the trick is trying to keep it within Yamaha's tolerances.
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Post by chrisg on Apr 24, 2020 21:01:21 GMT 1
I have just pulled the crank out this evening. OMG, its slipped about 20 deg and clearly visible.
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Post by steeley on Apr 25, 2020 4:56:51 GMT 1
Years ago i had a thought about having the parts in that area machined for a key way then pressed up .
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Post by marrcel on Apr 25, 2020 7:29:14 GMT 1
Any pictures of the welds on cranks guys?
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Post by Tobyjugs on Apr 25, 2020 8:50:08 GMT 1
Any pictures of the welds on cranks guys? This is from my +4 4LO crank (MK2) If you look carefully you will notice two welds.  |
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