Tips on reinstalling pistons

Spent most of today trying to replace rings on the pistons and reinstalling them. Broke the scavenger ring on one piston when I tried to get the jug on. Anybody got any tips to share on how to do this easily?

Thanks

Get yourself a ring compressor.

WTF is a scavenger ring?

the scavenger ring is the oil ring, if you're putting these in the 360 you have listed as your bike, the easiest helper is popsicle sticks, get the pistons lined up, lock the crank with a block or shop rags if you can, then gently work the block over the pistons, use the sticks to keep the rings in the ring grooves, also, what was your prep process on the block, pistons and rings before doing this?

Thanks for the feedback.

rockcitycafe said:

what was your prep process on the block, pistons and rings before doing this?

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Removed the pistons from the arm and removed the old broken rings. Cleaned the gunk out the ring grooves, checked the grooves for straightness and where out of line I sanded them smooth with 320/400/600. Polished the piston sides with 600 grit to make sure that they wasn't anything the would cause it to hang up or score. Cylinder walls were good, gave them a little polish with 600 grit. Washed everything with WD40 to remove any grit. Checked rings for fit and palm sanded as needed with 320/400/600. After installation of rings on piston, checked side gap and end gap. Then installed them back on crank arm and installed jug above. That's where the fun stopped.

I use an oil filter wrench to compress rings. But then, I'm too cheap to buy a ring compressor that probably does the job a lot better...

CLEAN the pistons WELL. Then use lots of lube and LOTS OF TIME, DON'T RUSH and don't FORCE THEM, the bottoms of the cylinders are tapered so you don't need a compressor, a cheap hose clamp will work though if you feel the need. Just go slow and work the rings into place as you go.

? you can't check end gap of rings on pistons
I usually polish the transition from lead at bottom of bore to bore, sometimes there is an 'edge'

already said, but hose clamps work magic!

Gratuitous use of assembly lube also helps.

Never use engine assembly lube on an engine that shares oil with a wet clutch. Some engine assembly lubes use heavy doses of friction modifiers like molybdenum. Bad mojo for clutches.

AlphaDogChoppers said:

Never use engine assembly lube on an engine that shares oil with a wet clutch. Some engine assembly lubes use heavy doses of friction modifiers like molybdenum. Bad mojo for clutches.

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Never had a problem with the stuff I use, but you make a good point. Good thing I read the labels on my shop fluids as much as I do the food I eat. Actually probably more so with the shop chemicals.

Molybdenum doesn't go into solution so it isn't a problem in small quantities.
It stays in suspension for a little while but ends up coating the bottom of sump
I use it on cam bearings and rocker pads without any problems (because they are high load area's and the oil is going to take a little while to get there, even if you kick it over for a while with the plugs out)

uhm... did you hone the cylinders?

also, as pj said, you don't check ring gap on the piston, you check it in the bore, about an inch down so its past any ledge caused by wear.

also, you did what to the ring lands??? you do realize that the ring lands bottom surface provides 100% of the sealing on the power stroke right? if it's not dead straight, toss the piston. unless you have access to some very good machinists instrumentation, you don't know if it's straight or not, and judging by your use of sandpaper, my guess is that you do not.

not to crap on your process first, but if you haven't put the engine back together yet, don't, go get some replacement oversize pistons and bring them and your block to a good engine machinist and have the work done right, there's no sense in putting it together and getting a bike that's unreliable

It's interesting that we all have our own habits which we swear by.

After a barrel is homed it should be washed out and dried with a clean rag. Wipe the bore with that clean white rag and if it comes out dirty, wash it again. repeat until all the ultra fine grinding debris is cleaned out of the microscopic pores on the metal.

I always use Redline assembly lube. It's not moly based, but in a pinch I'd use a Moly based lube. It's not like there's much being used.

Let's not open the How To Break In A Fresh Motor thread again, but let's just say we have a different approach. Swivel is right to avoid heavy loads on a fresh motor. I agree 100% on that aspect.

Back to rings. On a twin the trick is oil on the pistons to let them slide in, support the barrels on something and slowly ease one piston up into the bore. OR support the piston on a U shaped piece of metal across the crankcase mouth and slowly lower the barrels onto the piston. Hint: a set of pliers will also double as a piston support if your are lucky and turned on their side will hold up the barrels.

The key is to squeeze the rings in and take your time. It's fiddly and annoying, but think of it as a an exercise in remaining calm in difficult situations. A heavy barrel such as a 20 pound GT750 barrel is the same process but infinitely more annoying and tedious.

The wipe is to see how clean the surface is - not to clean it. It is an indicator not a guarantee. Let's look at it this way, if the white cloth comes out dirty, the bore is still dirty. What you are removing is any debris that has come loose in the last cleaning session and has adhered to the surface. Brush it with a toothbrush and good detergent to get the grit out.

I understand the rationale behind high speed low load. It just doesn't make a whole lot of sense, and neither does lugging a motor. That actually creates problems. Motors need to be run with increasing load and increasing revs. Race engines don't get a lot of running in though. A couple of heat cycles, a couple of laps at low load, reasonable revs, increasing revs and then load on the first session. Higher revs followed by more load on session 2 and go for it.

Race engines generally have a little more clearance than an engine that is built for long life, especially drag race engines.

Harley builds engines so tight these days, that they run hot and "feel tight" for 5,000 to 8,000 miles. An engine that is tight should not be run at high RPM even with no load, but that's just my opinion.

I know of no definitive study with regard to the relative merits of different break in methods. Fact is, it probably doesn't make much of a difference. Rings will seat no matter how the engine is run. Modern ring profiles and materials with precision bored cylinders mean they seal well right from the get go, and are probably fully seated within 50 miles. Pistons need a little more time to break in, IMO, and should never be stressed with high RPM, full throttle, or high temperatures until a 1,000 miles or so, but again, it's just my opinion and what feels intuitively right to me.

AlphaDogChoppers said:

Race engines generally have a little more clearance than an engine that is built for long life, especially drag race engines.

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All the info I have seems to contradict this. F1 engines, for instance, won't even turn over until they're heated up to 90°C. That seems to indicate VERY tight clearances. Differences between bikes and cars, maybe?

F1 engines are built for endurance, so it's an exception.

The longest race in F1 is Malaysia at just over 192 miles. There are 20 races in total plus practice and qualifying. So let's assume 192 * 20 * 2 (double the total distance to account for practice and qualifying laps) or 7860 miles in a season. F1 rules allow for eight engine changes per season and so that averages out to 960 miles per engine. That doesn't sound like endurance to me. Just sayin'.

That IS endurance when you factor how much horsepower they are generating. I think I read once that a typical NASCAR engine is completely rebuilt every 500 miles. AA fuel dragster engines are rebuilt after every 1/4 mile run, and the engine only turns over a total of 900 revolutions, including the burnout to heat up the tires.