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engine blow-by questions

mystryman said:
I tore down the top end on both cyls and taking them to shop to be bored and order new pistons. When I put it back together, do I need to use conventional oil for the break-in period?
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I Would use a Dino oil for the first run of 250 miles. Synthetic takes a LONGER time to do the Ring break-in IMHO and many builders...

250 miles is where I First change oil and filter Then back to MY Synthetic.
(this is on the New piston N ring replacement not a total NEW rebuilt motor)

Some will say 50 miles drain,chg filter...... some say 100 miles drain, new filter

BUT I say 250 miles Total,,change oil and filter and you are done... Back to the regular oil and changing oil and filter @ mileage U normally use...
ALSO, THEN, run it normal AFTER 500 miles on it total...

REMEMBER
Just My Way

signed....BUBBIE
 
mystryman said:
I tore down the top end on both cyls and taking them to shop to be bored and order new pistons. When I put it back together, do I need to use conventional oil for the break-in period?
Click to expand...

I have had the best results with quick ring seal with Shell Rotella 15W40. Lots of accel and decel for the first 50 miles, keeping rpms under 3500 and the rings should be seated. You can pick your own interval for the first oil change but I would not wait longer than the 250 miles per Bubbie's post; dump the oil but keep the filter. You can run the Shell Rotella for the first 1000 miles and when you can change to synthetic if synthetic floats your boat.

The machinist will need the pistons to fit them to the cylinders and the rings to gap them so when you get the parts back, all you need do is clean them up and put the motor back together. When you get the parts back, give the cylinders, pistons and rings a good bath in hot soapy water; they may look clean but there will be fine grit from the machine work which you must remove; cleanliness in assembly is often overlooked by the DIY guys. Wash the cylinders until you can wipe the cylinder walls with a white cloth and it comes away clean. Any smudging means the grit is still there. The liners will rust rather quickly so wait until you are ready to assemble to clean then coat the liners with some WD40 to stave off the rust until you get the top end assembled.

Do not use assembly lube on the pistons and rings; a light coat of oil is all that is necessary. One or two heat cycles after assembly for less than a minute just to listen for funny noises and check for leaks. I don't buy in t the 10 heat cycle program; riding the bike is the best way to seat the rings. Heat and compression under load is what seats the rings. As usual, JMHO.:D:hii
 
That's what I had assumed, but wanted to make sure. My repair book left that little detail out. It'll be about a week b4 I get the jugs back from the shop. I'm betting i'll be logging back on here when I start putting her back together.
thanks for all the advice.
 
mystryman said:
Sent original pistons with the jugs to the shop. ordering new set to match oversize when they're bored.
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Be sure to get the piston manufacturer's cylinder wall to piston clearance specs; don't leave that to the machinist. H-D pistons are cast hypereutectic and fitment is pretty tight. If another manufacturer, or forged, fitment specs will be different.
 
Machinist is doing what he calls a rough bore, which would be about .005 smaller than target oversize. Then he'll let me know what oversize to order and wait for the parts to finish up. I will be getting forged pistons.
 
I also photocopied a couple of pages from my service manual showing factory specs for pistons, rings, cylinders, etc. and took it to the shop.
 
After market pistons usually have different specs than OEM. If after market they should come with their specs as Dolt has stated. If you use OEM oversize then your manual specs would work. I have found that OEM piston/rings are usually cheaper than after market. You may want to compare prices.
tourbox
 
mystryman said:
Machinist is doing what he calls a rough bore, which would be about .005 smaller than target oversize. Then he'll let me know what oversize to order and wait for the parts to finish up. I will be getting forged pistons.
Click to expand...

Sounds like the machinist knows what he is doing. His rough bore will be whatever is required to achieve a true and round cylinder bore and he will hone for final piston fitment. I assume he is also using torque plates.

You really don't need forged pistons for your application. The OEM .010" O/S cast hypereutectic pistons are more than adequate, cheaper and can be setup at .0006"-.00015" IIRC. Forged pistons will setup at .002"-.004" depending on manufacturer and will typically be noisy on cold starts but quiet down when up to operating temps and everything has expanded. Of course, piston choice is your call. :hii
 
got the cylinders back. cleaned and oiled them. got bike put together today and went to fire it up. Now it seems like it wants to run on just the front cyl. front gets hot, rear barely gets warm. thought maybe I adjusted the pushrods wrong so I did that again...no change. hooked up timing light, its getting even fire. did a compression test, 105 front, 130 rear. huh?... so I did it again, same numbers....I don't get it.....I am really stumped now.
 
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