Balancing an 80mm 650 crank

plumbbob · Feb 8, 2014

Back on the scales, the piston is 270g and the rings 13g.

Here's a few pics of the piston,

[attachment=2:h0u2vnju]piston base.jpg[/attachment:h0u2vnju]

[attachment=1:h0u2vnju]piston side.jpg[/attachment:h0u2vnju]

[attachment=0:h0u2vnju]piston top.jpg[/attachment:h0u2vnju]

And even got the pics to show :cheers:

Taffy · Feb 10, 2014

I'd have gone for the taller and I guess heavier piston and got the squish right. those 2002s are miles away. look at the dished piston. it needn't weigh a helluva lot more...

regards

Taffy

plumbbob · Feb 10, 2014

Taffy said:
I'd have gone for the taller and I guess heavier piston and got the squish right. those 2002s are miles away. look at the dished piston. it needn't weigh a helluva lot more...

regards

Taffy

I'm just measuring what's in there, not changing anything that doesn't need changing.

Carl

berglsmerg · Feb 12, 2014

plumbbob said:
Taffy said:

I'd have gone for the taller and I guess heavier piston and got the squish right. those 2002s are miles away. look at the dished piston. it needn't weigh a helluva lot more...

regards

Taffy

Click to expand...

I'm just measuring what's in there, not changing anything that doesn't need changing.

Carl

Interesting ! perhaps you can measure the squish height for us all ? It's not difficult.

plumbbob · Feb 12, 2014

berglsmerg said:
Interesting ! perhaps you can measure the squish height for us all ? It's not difficult.

Can it be measured with the engine in bits?

Carl

Taffy · Feb 12, 2014

with the piston on the rod, in the liner, in the left case you can be reasonably close. with both cases together then you're good. in a knackered state...no. get the P & B and little end done first.

anyway, even a tall piston still misses the head by 2mm. this is with the 134mm C to C rod coded '164'.

regards

Taffy

bushmechanic · Feb 21, 2014

Crank Butchering

machining with carbide was painfully slow so i used a thin 5" cutoff disc $3.50 and all done in about 15 min. gotta love grinders

Dummy pin with a nice centre pivot to hang the bob weight, lead weight triangle substitues makes up the total weight of the real pin + rod + bearing, the bit of metal with holes in it is the bob weight

lighter rod.. a massive 30% lighter and its stronger as well ! I had hoped for more than 20gm but I chickened out with the grinder

Plumbob, Weed has let me know his 644 at 70% BF works fine and reckons 10% either side would also be OK

bushmechanic · Feb 21, 2014

this is Contimans crank

82mm stroke and welded pin.

plumbbob · Feb 21, 2014

Cheers Bushie,

I'm going to bolt it all up with the cb out (spacer instead) and see how it goes with my balance factor.

Carl

bushmechanic · Feb 21, 2014

sounds good

check out weeds spacer

with the smaller one he broke a lip off the bearing inner

second one has full support for the lip

bushmechanic · Feb 21, 2014

the old "fat" cranks of weeds and mine,

no problems with the welded weights about 200 hrs on mine .. weed even more I think.

so if you don't have a spare $800 to spend on Mallory or have fancy carbide drills a little preheat and some stainless weights work very well.

various lightened KTM RFS cranks, GWR DJH and others

and mine again, not quite as radical but not much work either and no expensive mallory

bushmechanic · Feb 23, 2014

lighter conrod ?

http://flashbackfab.com/how-to-build-a-racer/

lots of old school machining :cheers: :cheers:

Ghost · Feb 24, 2014

I wish I had a lathe. I do have access to one but since the owner is a sub contractor to Öhlins I'm not so sure they'd let me use it! :lol:

bushmechanic · Feb 24, 2014

lathes are amazing machines, It always spins me out how people where making reasonably accurate lathes and mills in the 1700s by hand, and with those machines they produced better ones... and so it went on until today when you can buy a computer controlled "mill" robot with less than 0.001mm resolution for less than the typical operators yearly salary 8O 8O

drive side pressed in and welded (more on how to weld later)

press the other side on 10mm or so and get both halves parallel by measuring in 3 spots and pressing more as needed

if you need to open it up somewhere use wedges

when its parallel check for twist between centres, mark the high spot on either side

take the crank out hold it by your rod and hit the un-welded (free) flywheel to twist it into the right place

recheck parallel and look for high spots again

when it not twisted your high spots will line up

happy with the twist, press it together. use a feeler gauge to help stop at 0.1mm bigger rod axial play than you want to have at the end. im going for 0.7mm so i set it at 0.8mm here

bushmechanic · Feb 24, 2014

welding the pin

the ignition side weld needs to be flush to clear the bearing and the bearing mount in the case

so grind a fillet out

make sure the crank is as true as possible at this point then put 4 tacks in

make sure the crank isn't twisted before you tack it. after tacking you can't correct the twist

preheat to 150C then use the weld shrinkage to keep the crank true as you weld, fill in a bit at a time and check how its going between centres

after the welding starts is is pointless to use force (press or wedges) to true the crank, you have to use the weld shrinkage only.

before checking the crank each time take a hammer and tap the crank around a bit to let it settle

I use a TIG welder with a foot pedal ER7OS2 filler rod and pulsed DC

welds on this one pulled the flywheel up.. sometimes they go down ..need to be aware

so if one side needs to come up (or down depending on its mood) just go over it again, nice big fillet with good penetration .. doesn't look very pretty

I keep a bucket of diesel ready and if I reckon its getting too hot i drop it in there for a while, you want to minimize the blueing if possible

ground down to clear the bearing and case

tourist · Feb 25, 2014

THANKS! I'm learning a ton of stuff here!

bushmechanic · Feb 25, 2014

me too

everytime i do this something new comes up, this crank wanted to open up with the weld shrinkage usually they close up. :?

maybe something to do with the different type of timing marks i drew.. opposite behavior of the rockets

berglsmerg · Feb 25, 2014

bushmechanic said:
maybe something to do with the different type of timing marks i drew.. opposite behavior of the rockets

There's ya problem right there.

tourist · Feb 26, 2014

So one thing that I've been mulling over - what if adjustment is needed later? Or if the conrod needs replacement?

Re. adjustment/change afterwards: Someone posted a picture of a cracked weld on a crank here - do you just grind out the weld and start over?

And if you need a new conrod? The same, or could the conrod be sawed or ground off without damaging the crankshaft? and then replaced with a conrod with a bolted big end? (correct term?) Or are the welds ground out like when you're preparing for the weld job on the ignition side?

bushmechanic · Feb 26, 2014

Hi tourist

yes you are on the right track

I grind the welds out of the ignition side then press the flyweel inwards so the rod axial play is zero

the end of the pin now protrudes a bit more so I grind the sharp edge off and then press it out as normal

same the other side if the pin needs replacing

or yes if the rod and pin are toast just cut the pin through the rod, much easier

my other crank in the 700 is on its 3rd pin

Cheers
Bushie

Balancing an 80mm 650 crank

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