spents obr 57 twin dragon hammer,

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bit more of an update (y), not had much workshop time lately cos of various reasons :LOL:,
but milled the fins on the new top ends so they fit the rcmk case ,
only three sides need machining , flywheel side for clearance, and between the two to bunch em up a tad ,



then the ribs on top need taking down so the heatsink fits,



took the ribs off, and bare minimum into the surface,,
i could have done with spinning em in the lathe to get perfect, but would take an age to set up with 4 jaw chuck etc,
so theres a 0.15mm square that needs dealing with around the plug holes,



tops are perfectly flat and even, but gonna do two 0.15mm or 0.2mm square pockets in underside of the heatsink so it sits flush to the heads (y),
then need to mark then drill and tap the four mounting holes for the heatsink,

 
Looking good Paul, can't wait to see it rip!
thanks ryan (y) , yeh i wanna see it rip again an all (y) :D
So your next jig is gonna be one that you can bolt the heads onto in the lathe to turn head ribs off then.
Looks good spents
yeh in hindsight i shoulda centralised everything on this jig kev,
only a couple mm out, and could use this one with 4 jaw independent chuck (y) ,
plug holes dead centre so i've also modded an old piston stopper for a live centre to run in on the lathe
 
right, so back at doing some stuff, easing back into it after yet another injury thats taken around 6 weeks to get sommat like good again 🤦‍♂️:ROFLMAO::ROFLMAO:,
anyways, the twin bottom end,
bit of a story but stick with it :D,
now this engine has always tightened up when not used, then when its fired up again its slackened off,
this time when i renewed the crank bearings and the seals it was tight from the get go,
new bearings are correct as are the seals for size and dimension s etc,
i always assumed it was just the crank seals getting tight on the crank after it was sat a while,
but looked a bit deeper and took some very precise measurements of the bottom end well as precise as i could with what i have available,
now there was zero end float on the crank, and it seemed to be nipping the crank ever so slightly when cases were torqued up fully,
so disassembled bottom end, centre bearings and centre seals are smooth as you'd want (y), so the centre section was left assembled,
but i have removed 0.3mm material from the outer bearing seats so thats 0.15mm each side so the outer mains sit a liitle deeper,
this leaves just under 0.5mm of bearing protruding into the case, it was just over 0.5mm before,
reassembled the bottom end without the seals at first and torqued the casings down proper, smooth as ya like and have 0.1-0.15mm end float now,
so going off my calculation that means that the crank was super tight and side thrust was being applied to the outer main bearings making it tight,



disassembled again and refitted the seals and made sure bearings were fully seated etc,
then back together again and torqued fully again and its buttery smooth with the 0.1-0.15mm end float on the crank,
so i'm gonna take that as a win and will see what happens down the line if it does go tight again,
i'm now 100% certain it was putting side thrust on the outer bearings now and that was part of the reason for the tightness, no notchiness felt when pulling over, was just tight, plus seals gripping the crank when left a while as well,
and going off the condition of the old bearings it does seem side load was on em with how they were worn,
so am back to where i was with it again with the bottom end assembled, but nice and smooth now (y):D,

 
Good detective work Paul 👏 glad you got it sorted
yeh its sommat thats always bugged me ryan, and tbh with the amount this engines been ragged across fields i'm surprised nothing broke before now,
but its way better than it ever was from new with how smooth the bottom end is now,
i've always had suspicions that sommat wernt quite right with this engine from new though, but just assumed it was normal for the twin bottom ends,
it always ran great once it was running, but always had issues starting it if it had been left a while, but tehen would start first or second pull once it had been run,
if sean sees this will see if he agrees maybe sommat wernt right or not (y):D
 
Glad you caught it and im surprised it didn't show itself earlier with some sort of heat color building up somewhere
thanks ryan (y) , and yeh i thought the same, but no heat colouring found anywhere on the bottom end,
all i can think is the old bearings wore a bit with side load and when i fitted new bearings it went super tight again,
the old bearings are worn that way as well,
i must have got very lucky is all i can think (y):LOL:
 
Definatly need a bit of end play. Good catch spents. Had to be hard as fek on the bearings. Bet she will get a few more r's as well.
yeh the old bearings had plenty play in em sean :ROFLMAO:,
but side play not verticle play if that makes sense,
hopefully it runs better than ever when its back together again,
i also have new carbs that just need modding on the throttle shafts etc t take the carb to carb linkage,
so the engines gonna be freshened up proper (y)
 
little bit more done today,
i reworked the milling jig so it would centre in the lathe as well,
then spun the final left over bits of the stubs off ,
then marked, drilled and tapped the holes for the heatsink (y),



heatsink fits bob on, had to take my time with the mounting holes cos there aint much room for error :LOL:,
its a case of heads on off on off at the moment,
pistons are next job, gonna cut the relief same as the original obr ones,



 
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