Hey guys...
What an interesting day it has been... Not in a totally pleasant way either...
I unpacked the crank at around midday, at quick glances, it appeared a tad "rough" ... nothing like the finish on the original, not that that was very good to start with....
After about 2 hours of filing and de-nubbing, this is what it looks like,
http://www.warriorpaintball.co.za/private/Replacement Crank 20151223 .... Not great, but usable.... I wish I had a larger lathe to smooth down those terrible cuts that were made... overall, everything was in basic spec, but the finish was atrocious... The big end journal was coarsely ground, way too rough for my liking, but slightly over size thank goodness... after a few hours with 1000 grit water paper and a buffing/polishing wheel, it is now almost ready for installation... A point to note is that whilst assembling and testing clearances, I kept on picking up swarf in the bearing shells, no matter how clean I made them. I eventually tracked the problem's cause... the lube hole was badly cut, with swarf chip welded to the inside of the passages... I reamed the exit hole with a sharp 7mm drill and then discovered that the entrance hole, while starting at 10mm, narrowed down to a 5mm pilot hole after about 15mm... this would have effectively negated the ring feeders action as the oil would have to flow "uphill" against centrifugal force, to exit into the big end bushing.... this might be something to check on if you have a similar oil feed system...
I have 2 x .1mm shims on one side of the conrod bearing half, and one .1mm shim on the other... with one shim in each side, when torqued to spec, the bearing locks solid in all positions... my thinking is that putting in one shim extra on one side, gives me half of .1 clearance overall, ie, .05 mm final bearing clearance... this equates to less than 3 thou, so it should be OK... What concerns me a tad, is that there is a TINY bit of ovality in both the journal and big end... at 2 points of rotation, there is a slight bind, easy to overcome with mild hand force, but a bind nevertheless... I will take alook at it tomorrow if I have the inclination, but it its so slight that I might just leave it and run it as is.... your thoughts gentlemen?
I also noted that the removal of the old main bearings was, shall I say, somewhat tedious.... I estimate about a .10 -.15mm interference fit, judging by the effort to get them off... I definitely am going to check and mic the seat areas before I refit them to the new crank....(yes, I did keep the inner/outer bearings as matched pairs and have marked them as such to keep them so) .... That amount of interference is totally over the top for this or any application like this.....
Next step is to install the crank and set up the end float, once the mains are in place, I will be looking at around 3 thou cold float, it should be adequate and not too excessive... Previous float was....duh... none.... after 1600 hrs of runtime, it was still tight to turn, almost too tight to turn by hand without conrod or flywheels on... So much so, that when I stripped the trumpets off, I checked them for cracks.... I see some creative scissor work in my immediate future, making additional spacers from paper....
I eventually got the sh!ts with trying to find Torque and Clearance settings in the piles of notes I have dotted around the workshops... I put together this "cheat sheet" for my own reference, help yourself if you want a copy, it is a "concentration" of all my scraps of notes that I have on this engine and a couple of others, use at your own risk etc etc etc.... If you spot something that I have cocked up or left out, don't hesitate to shout... you can find it here
http://www.warriorpaintball.co.za/private/Cheat SheetAnyways, again I ramble on, I hope u guys are getting some entertaining reading if nothing else from my mutterings and ramblings...
Keep it spinning..
Regds
Ed
PS... I also took some weight measurements of the crank, remember, this is a 12hp idi cbw engine, so if yours ain't the same, well, nuff said...
Crank with cbw and conrod installed - rotary mass, 700g, under balanced
Oscillating masses:
Gudgeon pin and circlips - 500g
Piston, aluminium, - 1645g
Rings - 210g
Small end mass - 1000g
Top ring(additional to be installed) - 25g
So my guess at counterweights to be added would be:700+(500+1645+210+1000+25)/2= 700+3380/2=2390g at crank throw radius to give 50% balance throughout the rev range... cmon Chris, does it look about right to you from a calculation POV?(also, my flywheels have no built in balance weights...)
PPS - Cheat sheet has been updated - Copy available here:
http://www.warriorpaintball.co.za/private/Cheat Sheet
