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Re bore questions #747875
09/04/18 11:54 am
09/04/18 11:54 am
Joined: Aug 2015
Posts: 86
Gippsland, Vic, Australia
M
mickjmag Offline OP
BritBike Forum member
mickjmag  Offline OP
BritBike Forum member
M

Joined: Aug 2015
Posts: 86
Gippsland, Vic, Australia
Hi All,

Sorry if this topic has been done to death but its my first time attempting a re bore!
Have just got my self a new set of JCC pistons and Hastings rings +040 ready for a rebore, on my 65 thunderbolt rocket.
the old pistons were +020 and blowing a good amount of smoke from both cylinders under load, esp.. the rhs, this was due to corrosion marks low down on both bores, as this bike sat for a long time in the states before it was resurrected, also some scoring on both pistons that looks like it might have gotten a bit warm at some stage,valves & guides are good, no play evident no evidence on back of valves of oil! and only 1000 miles since I o/hauled the head.
My question is what would be a safe piston/ bore clearance for the JCC +040 set up also ring gaps, new pistons measure 2.988 at bottom of skirt 90 deg from pin and 2.983 under the oil ring groove
I ride the bike mostly on short trips and the odd long haul at no more than 65mph so its never under any major duress so fingers crossed this re bore will give me many happy miles smile

Cheers, Mick


Mick M, in OZ
1965 Thunderbolt Rocket.
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Re: Re bore questions [Re: mickjmag] #747928
09/04/18 9:54 pm
09/04/18 9:54 pm
Joined: Jan 2014
Posts: 4,099
Aus
N
NickL Online content
BritBike Forum member
NickL  Online Content
BritBike Forum member
N

Joined: Jan 2014
Posts: 4,099
Aus
4.5 thou piston clearance is the norm with a 10 thou ring gap.


No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Re: Re bore questions [Re: NickL] #748004
09/05/18 4:52 pm
09/05/18 4:52 pm
Joined: May 2013
Posts: 5,082
Rotherham - S. Yorkshire
Allan Gill Offline

BritBike Forum member
Allan Gill  Offline

BritBike Forum member

Joined: May 2013
Posts: 5,082
Rotherham - S. Yorkshire
Originally Posted by NickL
4.5 thou piston clearance is the norm with a 10 thou ring gap.


plus 1


beerchug
Re: Re bore questions [Re: Allan Gill] #748174
09/06/18 9:52 pm
09/06/18 9:52 pm
Joined: Aug 2015
Posts: 86
Gippsland, Vic, Australia
M
mickjmag Offline OP
BritBike Forum member
mickjmag  Offline OP
BritBike Forum member
M

Joined: Aug 2015
Posts: 86
Gippsland, Vic, Australia
Thanks Guys,
Once again this sites info has made a daunting task easy grin
Stuck the barrel in the mill and bored it out and finished of with a 180 grit bore hone .0045 clearance no dramas!
Dry assembled the pistons and rings as published in other threads reset valve clearances and am stoked to say that after the first 50 kms all is good, running just as good before strip down, but with no smoke no rattles and plugs are looking pretty good, maybe a tad on the rich side but will leave for the moment.
Will take it out for another blast after work today then do a re torque on the bolts drop the filter and get some fresh oil in it for a good ride on the weekend thumbsup.
Once again thanks to all for the info.

Cheers, Mick


Mick M, in OZ
1965 Thunderbolt Rocket.
Re: Re bore questions [Re: mickjmag] #748265
09/07/18 6:45 pm
09/07/18 6:45 pm
Joined: May 2013
Posts: 5,082
Rotherham - S. Yorkshire
Allan Gill Offline

BritBike Forum member
Allan Gill  Offline

BritBike Forum member

Joined: May 2013
Posts: 5,082
Rotherham - S. Yorkshire
Sounds great Mick!!

the barrel I'm running with now was bored to the later spec of .004", unlike the .0045 it would start getting fussy and wanting to cool down when running in, once run in it was fine but never had an issue with the .0045 and always try and keep to that value.


beerchug

Moderated by  Allan Gill, Jon W. Whitley 


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