RB20 fit

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Grumpy225
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Sun Apr 19, 2020 3:19 am

Replaced my RB20 cylinder after my crank rod exploded and the new cylinder is having a hard time sitting all the way home on the case. I’m doing the initial dry build to set the port timings with the new 115/60 cranks. It looks like the upper kick side stud hole might be a hair off where it should be.

Old cylinder stamped # 95 fits no problem with all 4 studs in place.

New cylinder #630 gets super tight on the cylinder studs at around 20mm above the case but will drop right down with just 3 studs in place. Studs (MBD type) are straight.

Has anyone seen this on the RB20 kit before? No gaskets or piston in place at this stage. I think I can open up that stud hole enough to release the tension on it but wanted to see if anyone else had run across this.

Scooterdude
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Sun Apr 19, 2020 8:33 am

I’ve had the reed block contact the engine mount when fitting these that require a bit filing off the corner but guess it isn’t that or you would have noticed .

If you’re using the mb fat studs their a nightmare, best thing to do is bin them and fit either vespa or the long Scootopia studs that are now available.

holty
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Sun Apr 19, 2020 12:31 pm

I built an rb20 for a friend of mine and had exactly the same problem with those studs, he was advised by the person he got them from to drill the holes out in the brand new barrel, I advised him that I wasn't doing that and got some thinner studs, its also a well known problem for the 4 point seize so I would change studs no question

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kevspeed
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Sun Apr 19, 2020 1:27 pm

holty wrote:
Sun Apr 19, 2020 12:31 pm
I built an rb20 for a friend of mine and had exactly the same problem with those studs, he was advised by the person he got them from to drill the holes out in the brand new barrel, I advised him that I wasn't doing that and got some thinner studs, its also a well known problem for the 4 point seize so I would change studs no question
Same here 8-) 8-)

Grumpy225
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Sun Apr 19, 2020 3:31 pm

Thanks for the input. It’s crazy that on one kit there’s no problem but there is on the other with the same studs. I’ll see about finding some scootopia studs and at least start there.

Thanks

10 inch Terror
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Sun Apr 19, 2020 6:05 pm

When I built my RB20 a few years back I had exactly the same issues using the MB studs. From memory I ditched those and fitted some ‘standard’ ones and just used the nuts and washers that came with the MB studs. I hope this helps Pete.

10 inch Terror
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Sun Apr 19, 2020 6:27 pm


Adam_Winstone
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Sun Apr 19, 2020 6:43 pm

;)

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rosscla
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Wed Apr 22, 2020 12:30 am

Put the standard studs in
"Our dilemma is that we hate change and love it at the same time; what we really want is for things to remain the same but get better."

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garry inglis
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Wed Apr 22, 2020 4:19 pm

same here i used the standard studs from rayspeed as original 7.3mm thick rolled steel studs

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