Bear with me as these might be very very basic questions…but is something I have not done before. My mechanical aptitude is relatively good for general kart items, but stops at the motor internals.
I had my engine torn down in tech after the last Stars race (good), but have not re-assembled one before (bad). Normally, I just send it to BBS as every other time it’s been due for at least a top end. However, I still have some time left before a rebuild is due and would rather not incur the bill for one more race weekend just for a re-assembly.
I’ve downloaded and printed the IAME KA100 overhaul manual and watched the Youtube videos (https://www.youtube.com/watch?v=EHKmalPMNks), but figured there is enough knowledge here to help me beware of any pitfalls or ill-advised attempts on my part.
-If I am just re-assembling the motor, would anything potential fall out of spec from before tear down?
-Any specific measurements that I should be making during re-assembly? I’m planning to check the piston ring gap and squish, at minimum.
-I was planning to replace, at the very minimum, the head o-ring and piston circlips (purchasing the appropriate tool). Are there any other parts (perhaps the wrist pin or roller bearing) that should be changed more frequently?
-I was planning to leave the base gasket(s) “as is”.
-Any other traps that I need to be aware of / questions I’m not asking?
Or, am I being an idiot and should just cough up the dough for BBS to go through it again?
What a wonderful question, almost existential! I know what I’d do - reassemble and make that a test of my skills! Trying something is the only way to know whether I can figure out something or not. Depends of course what you have too loose. Confidence in yourself.. your next race… money… But I know what there is to gain: Driving something you’ve fixed yourself is a great pleasure. Whatever you do, good luck!
Might sound silly, but ensure that the piston is re-installed facing the correct direction, and that the ring and bore are in good condition…no scoring on the bore and/or piston, no flakes/chunks of ring material or plating missing.
Wrist pin and small end bearing will go the life of the piston no problem. Changing any circlips that were removed is a good idea. If one side was not removed, then I would leave it as-is. Base gaskets that are in good condition can be reused, provided they haven’t compressed to the point that you would fail a squish test. Of course, be sure to torque the head properly.
As Evan noted replace any circlips that were removed. You’ll want the fancy tool to do that without wanting to murder someone. I’d only worry about the wrist pin and upper bearing if they show signs of abnormal color or wear.
Base gaskets obviously replace any that are torn, but also re-torque the head and check squish to see if any new ones are needed otherwise.
Coat everything with 2-stroke oil whole reassembling (put a little on the big end bearing while you’re at it) and pay very special attention that the ring stays aligned with the locating pin and doesn’t shift when installing the jug. Take your time and you’ll be golden.
Should have posted this a week ago…i was in Pitt for work and would have stopped out and put it back together for you and shot the shit vs. corporate BS I was doing.
While you can get creative with what to use for installing the piston pin, the appropriate tool is pretty cheap and comes in handy. Aarow on the top of the piston goes to the exhaust port as Evan mentioned. You can get a 14mm circlip installation tool through Mondo for about 1/3 of what the IAME tool costs..not sure what the import tax situation is with the most recent changes though. I think Fastech or Accellerated also had the generic (gold) tool for less than the IAME one.
I’ve gone both ways on the base gaskets, odds are you are ok to reuse and takes some of the guess work out of how much any of them may have compressed during use.
Get the proper solder for checking squish and make sure you’re checking both sides directly above the piston pin when measuring. If you completely clean the top of the piston and all the carbon off the head Brian’s motors usually measure .043 to .044 when they are fresh and clean,
Figuring out how to pinch the ring around the locating pin to install the piston the first time takes a minute to figure out but once you get it down it’s easy. Basically set the cylinder onto the studs then hold the piston with the ring compressed around it a bit with one hand as you lower the cylinder with the other. Tilt the piston slightly so that the exhaust side (away from the locating pin) enters into the bore before the front and you should be able to easily rock the piston while squeezing the pin into location with very little effort from there.
Make sure you’re working in a clinically clean environment and using lint free rags, I use maroon scotch brite pads for cleaning carbon off the top of the piston and head along with simple penetrating oil like WD40. Get a quart of Maxima 927 caster oil and lube everything with it as it’s going back together.
Torque values for the head and exhaust manifold are critical to bore deformation, follow the spec and you will be good. Re-Torque the head (cold) after the first couple sessions on the motor.
Evan, Chris, and Andy - thank you, gentlemen. This is exactly what I needed. Appreciate the thoughtful responses. I figured it is easy enough and that I was likely overthinking it, but would rather be safe than sorry and experience a failure. KartPulse community always comes through.
@Andy_Kutscher - let me know next time you’re in Pittsburgh! Even if I don’t have a motor for re-assembly, can always find the time to grab a beer downtown or hang in the garage.