Is this normal after a rebuild?

[arudeseal]

http://dl.dropbox.com/u/16615716/20120811_165904.mp4

It's making me nervous. New pistons and rings. About 50 miles after top end rebuilt. It's the breather tube. I put it up against the black part of the engine to show contrast.

 

[teazer]

Short answer. No. I could make the argument that it takes time for new rings to bed in, but my new car didn't smoke at all so why should a rebuilt bike. Is the noise normal? It almost sounds like a broken piston ring, but could just be the microphone on that camera distorting the sound.

What was done in that "rebuild"?

 

[neevo]

Teaser wouldn't incorrect gap or wrong placement of ring gaps also cause this?

If the bikes been run for 50 miles you would expect the rings to be run in enough unless the motor was completely babied.

 

[teazer]

Good questions.

If ring gap were huge, it would pump like that. Ring gaps alignment is a bit of a myth though. I read a while ago that rings rotate in service, so they line up from time to time anyway and then rotate back so they no longer align. It's smart to assemble the engine with the gaps at 120 degree spacing though.

It really depends on what was done when it was rebuilt. If it was tripped and then reassembled with the same parts and maybe with rings upside down, that's possible. Could be the bore is out of round or pistons are re-used in a bore that's worn or... So many things to speculate about. I'm sure when the OP tells us what he did and didn't do, we should be able to work out what's up.

 

[elbes14]

sounds to me like your pistons tapping a valve. You sure your timing isn't slightly off?

 

[neevo]

Ring gaps alignment is a bit of a myth though. I read a while ago that rings rotate in service, so they line up from time to time anyway and then rotate back so they no longer align. It's smart to assemble the engine with the gaps at 120 degree spacing though.

Ah I assume the pistons don't come with gap pegs then. All the pistons I've put into modern bikes did which meant ring rotation wasn't a thing to think about.

 

[teazer]

All two strokes have pegs to stop the rings from getting trapped in the ports. It's unusual to have pegs in a 4 stroke piston ring groove.

 

[neevo]

All two strokes have pegs to stop the rings from getting trapped in the ports. It's unusual to have pegs in a 4 stroke piston ring groove.

Well I did not know that. Thanks teazer, I am now a little wiser as of today

 

[AgentX]

Good questions.

If ring gap were huge, it would pump like that. Ring gaps alignment is a bit of a myth though. I read a while ago that rings rotate in service, so they line up from time to time anyway and then rotate back so they no longer align. It's smart to assemble the engine with the gaps at 120 degree spacing though.

From performance guru Tom Lyons of Ace Engineering, LLC:
---
We normally make sure that the gaps are not aligned when installing, and try
to keep the gaps to the sides, away from the thrust faces of the bore when
assembling.

This is to help reduce any possibility of scratching the bore on initial start
up. The rings will rotate in use, and the issue of gap alignment is not an issue
after the engine is going. We are just trying to prevent potential scratches in
the initial start up procedure

---

Anyone who's been in the military has had the alignment myth pushed about the gas rings on his M-16, as well.

 

[elbes14]

This a 2 stroke or a 4 stroke bike?

 

[arudeseal]

New gaskets, new cam chain and tensioner, cylinders honed, new piston rings and pistons. Cylinders were well within spec, so no bore was needed. Valves were all true and within spec. Carbon cleaned from combustion chamber.

Warm compression is 195 on both cylinders. The smoking starts after about 15 minutes of riding. Valves and timing were just set.

 

[arudeseal]

Bike is a 70 cb350. The confusing part is that I have great compression. Wouldn't a broken ring, cylinder out of round, hole in piston also cause the compression to drop?

 

[surffly]

Isn't 195psi over spec? Check the manual.
Did you change the valve guides or seals? Valves lapped and installed correctly?

 

[SONICJK]

195 is way high.....

 

[surffly]

Yup just checked my manual, Honda wants 170psi
So something is defiantly wrong

Unless you are using a cheapo gauge, and then its anyones guess

 

[SONICJK]

Yup, 170 is about perfect

Did you leave out a gasket? Forget the base gasket?

 

[arudeseal]

All gaskets are in and brand new. Used copper sealer on the head gasket. The only servicing done to the valves was lapping. Everything else was well within spec on them. Had a buddy bring over his professional compression gauge (mine was from harbor freight) and got 175 on both cylinders. So to recap....new rings, new pistons, honed cylinders, piston to cylinder clearance was good, ring gap clearance was good (measured by placing new rings into cylinders and using a feeler gauge), valves freshly lapped, new gaskets, valves set and timing set. Compression good. I am freaking stumped. Any other ideas of what I should check?

 

[elbes14]

The ticking and the high compression let me to believe your timing was out a tooth either way, but now that you have checked it and its bang on i'm kinda stumped as well...

 

[ktriple]

how was it "broken in"? if it was eased in, do the opposite and run it hard. put a heavy strain on the engine, vary the rpms, as in get them up high (under load) and then drop back down, preferably coasting the bike at high speed back down to lower speeds. if the rings havent been seated properly, this may do it if it isnt too late.