Cruzin image ebay pistons

[bpupeza]

I got these pistons and they are a little different. The oil holes are smaller for one. On the pistons that were in the bike the top and middle rings are two different thicknesses on the new ones they are both the same width although one ring has an all over black coating and the other one has no coating on the outside diameter only on the flats. The manual says that there should be no side gap whatsoever on the oil rings. The new one I can shove a .004” shim in it.

 

[TwoManyXS1Bs]

The silvery-edged ring would be the top ring.
Are they marked to show which side is up?

The oil control rings, assembled on the expander, should measure 2.8mm (0.110") thick.
Yes, no side gap. Might consider returning these.
Measure/compare the groove widths.

You can put a wristpin halfway into the old piston, slide the new piston over the protruding half to line them up, then compare groove, skirt, and deck heights...

 

[xjwmx]

Several ppl here have used these pistons, and I haven't read any bad reports yet. The no gap vs .004", these are different pistons and rings from stock. I would probably research allowable tolerance on oil rings in general and not reject them if they fall into those broad guidelines.

 

[Ratranger]

I didn't check the oil rings when I put them in my bike. But the 1st and second rings showed up dead middle of the end gap specs, and about 1k miles no smoke, no extra blowby, and were very closely matched out of the box.

Are these stock size or oversize? Cylinder wear could be part of it.

 

[bpupeza]

The silvery-edged ring would be the top ring.
Are they marked to show which side is up?

The oil control rings, assembled on the expander, should measure 2.8mm (0.110") thick.
Yes, no side gap. Might consider returning these.
Measure/compare the groove widths.

You can put a wristpin halfway into the old piston, slide the new piston over the protruding half to line them up, then compare groove, skirt, and deck heights...

The rings are marked. Whats the purpose of the coating or lack there of on one ring?
The deck height looks good.

 

[bpupeza]

I didn't check the oil rings when I put them in my bike. But the 1st and second rings showed up dead middle of the end gap specs, and about 1k miles no smoke, no extra blowby, and were very closely matched out of the box.

Are these stock size or oversize? Cylinder wear could be part of it.

They are second over and I already had my bores done to match.
The end gaps are good on all of the rings. Side gap is good on top and second rings. Its just the side gap on the oil control rings that concerns me.

 

[xjwmx]

I might be pitting myself against a better mechanical mind here, but from what I can tell you all are wrong about zero side clearance allowed on the oil ring. First, it does not make sense -- things are manufactured with a tolerance. Also,, unless I misunderstand, it appears that you're taking the absence of a spec in the manual to mean zero allowance. I would actually sooner take it to mean any clearance is okay. But I think they just accidentally left it out of the manual. I did find this spec in a rarer international manual, although it looks a bit misprinted too.

 

[bpupeza]

I might be pitting myself against a better mechanical mind here, but from what I can tell you all are wrong about zero side clearance allowed on the oil ring. First, it does not make sense -- things are manufactured with a tolerance. Also,, unless I misunderstand, it appears that you're taking the absence of a spec in the manual to mean zero allowance. I would actually sooner take it to mean any clearance is okay. But I think they just accidentally left it out of the manual. I did find this spec in a rarer international manual, although it looks a bit misprinted too.

View attachment 145543

Your chart says that the side clearance is -.03 and + .01. I find it odd to have a negative clearance unless it is suggesting that it can have a force fit of .03 and .01 clearance. Either way I am well beyond .01 but I think I will take my chances considering that I already have my bores done. I am guessing many people didnt even check it before they installed them.

 

[GLJ]

I've got 850 miles on an engine with Cruzinimage 2nd over pistons in it. Very happy with them.

Whats the purpose of the coating or lack there of on one ring?

The one that looks like it has no coating is the chrome ring. It goes on top. It's chrome because of the higher temp at the top ring.

IMHO .004 side clearance on the oil rings is just fine. Keep in mind these are not 40 year old OEM pistons. So the Yamaha service manual may or may not be correct for all the specs. Cruzinimage piston/rings are clearanced per the ring manufacture.

 

[bpupeza]

View attachment 145516 View attachment 145510 View attachment 145515
I got these pistons and they are a little different. The oil holes are smaller for one. On the pistons that were in the bike the top and middle rings are two different thicknesses on the new ones they are both the same width although one ring has an all over black coating and the other one has no coating on the outside diameter only on the flats. The manual says that there should be no side gap whatsoever on the oil rings. The new one I can shove a .004” shim in it.

Thanks everyone for your advice.
The only thing that I am still wondering about is the smaller oil holes than original. Does the oil just slosh around in there and basically leak through the holes or is the oil under pressure and squirt through the holes?

 

[xjwmx]

There's no way for pressurized oil to get to the holes.... I would think the size and number of holes is fairly arbitrary.
Oiling diagram.

 

[GLJ]

I am still wondering about is the smaller oil holes than original.

Never thought about why they are there. Did a little searching and the best I can tell is they create a easy path for oil to return to the crankcase during the downstroke.Why Cruzinimage pistons have a smaller hole I have no clue. Have not read a bad thing about them here. The ones I have installed have had no problems.
Install and enjoy.

 

[Ratranger]

I agree that it should be fine. Plenty of people running them with no issues. I've got 2nd over in my bike, I checked them over with micrometers and a scale that went to .01 grams. They were matched within .0005" and .1g with pins and rings. Overall from my experience and reading others they are very good quality for the price. I've even got a set sitting here to go 466 big bore on a cb400f and they are just as good on tolerances.

 

[TwoManyXS1Bs]

...The only thing that I am still wondering about is the smaller oil holes than original. Does the oil just slosh around in there and basically leak through the holes or is the oil under pressure and squirt through the holes?

Yup, basically just leaks thru the holes.
It falls under the catagory of "splash oiling".

Can't tell from your pics, but you'll want to ensure that there's also oiling holes in the oil control ring grooves, like this pic.


A manual snippet explaining those oiling holes.

The size of the holes isn't critical, just so they're there.

The side clearance callouts for the top 2 rings is part of the sealing science of piston rings, to resist high-pressure blowby of combustion pressures, but allow a tiny amount of that pressure to get behind the rings and press them against the cylinder wall. But, not so big as to allow ring "flutter", battering of the piston ringlands.

The side clearance callout for the oil control rings is just to ensure confining the oil to between the 2 rails, and to avoid the same flutter/battering.

The manual snippet of ring side clearances, showing zero for the oil control rings.

The springy expander spacer ring is supposed to gently press the 2 rails up/down to get that zero clearance.

Another snippet, describing the expander spacer.

So, those are the manual explanations, from 40-50 years ago.

If the oil control rails aren't being pressed up/down against the piston lands by the expander ring, I would expect a loss in oil control. Could get a little smoking, or not enuff to detect.

As far as I can tell, you're the first to notice this. Everybody else has had good results with these piston kits, maybe you will too. If not, please let us know...

 

[bpupeza]

Yup, basically just leaks thru the holes.
It falls under the catagory of "splash oiling".

Can't tell from your pics, but you'll want to ensure that there's also oiling holes in the oil control ring grooves, like this pic.
View attachment 145580

A manual snippet explaining those oiling holes.
View attachment 145581

The size of the holes isn't critical, just so they're there.

The side clearance callouts for the top 2 rings is part of the sealing science of piston rings, to resist high-pressure blowby of combustion pressures, but allow a tiny amount of that pressure to get behind the rings and press them against the cylinder wall. But, not so big as to allow ring "flutter", battering of the piston ringlands.

The side clearance callout for the oil control rings is just to ensure confining the oil to between the 2 rails, and to avoid the same flutter/battering.

The manual snippet of ring side clearances, showing zero for the oil control rings.
View attachment 145582

The springy expander spacer ring is supposed to gently press the 2 rails up/down to get that zero clearance.

Another snippet, describing the expander spacer.
View attachment 145583

So, those are the manual explanations, from 40-50 years ago.

If the oil control rails aren't being pressed up/down against the piston lands by the expander ring, I would expect a loss in oil control. Could get a little smoking, or not enuff to detect.

As far as I can tell, you're the first to notice this. Everybody else has had good results with these piston kits, maybe you will too. If not, please let us know...

That is certainly an in depth manual!
Its clear that there shouldn’t be any side clearance on the oil ring.
I have not assembled the rings on the second piston yet. I think I will check that one and then message the seller. If he is of no help I will probably just go for it based on the success of the many other users.

 

[xjwmx]

What manual do you guys have with that oil ring info? Not saying you're wrong, saying I want all the manuals Mine I think is for '78 with supplement books up to '81. No mention at all of the oil ring side clearance, so might mean it's not very important in practice.

 

[Ratranger]

Clymer has way more info than haynes. I have both and the clymer is way better and has specs where haynes doesn't.

 

[xjwmx]

What I'm seeing though has that weird font and bad pictures of a factory manual pdf.

 

[TwoManyXS1Bs]

What manual do you guys have with that oil ring info?

You'll find it in the early manuals, 70-74 combined and the '75 manual.

As 5twins has mentioned in other threads, best if you can get as many manuals as you can, factory and aftermarket. Plus membership in this forum.

A re-posting from an older thread:

I've seen a disturbing trend in the evolution of manuals and schematics spanning from the '60s to the 2000's. Motorcycle manuals for asian imports back then were often oddly translated renditions similar to the strange Chinese instructions found with import gadgets. Automotive manuals, on the other hand, provided a lot of 'theory of operation' for various components, like a complete description of how the internals of a Delco alternator worked, or the hows and whys of setting the critical advance curves of distributors. Folks back then seemed to have a better grasp of how and why things worked.

I've found the modern manuals omit these 'theory of operations', and have supplanted them with endless repetitions of "disconnect battery negative ground" plus other idiot-proofing disclaimers of safety, to satisfy an ever-increasing litigious business environment.

Schematics can be classed in three systems:

Logical - Where the circuit layout reveals the logic and functional understanding of how things work.
Physical - The wiring layout for specific vehicle regions or zones. Attuned for factory assemblers and techs trying to find connectors and such.
Harness - The actual loom layout, attuned to harness manufacturing.

Older manuals showed 'logical' schematics, which greatly aids understanding in diagnosis. You're on your own to find the connectors.
Newer manuals show the 'physical' schematics, you can quickly find the connectors. But, unless you know what's the problem, or successfully follow the cookbook troubleshooting charts, about all you can do is replace parts until it's fixed. Parts departments love this, sells more parts.

Newer automotive manuals have to include an ever-increasing array of ancillary systems that don't relate to the primary purpose of the vehicle, like emissions, air-bag safety equipment, exotic convenience gadgetry, 12-speaker sound systems, security, ...etc. Today's tech has a much higher taskload on these newer vehicles.

But, the trend I've been seeing here is a move away from 'understanding and repairing' to automatons that simply replace parts. A shrewd business strategy.

 

[TwoManyXS1Bs]

...Mine I think is for '78 with supplement books up to '81. No mention at all of the oil ring side clearance, so might mean it's not very important in practice.

Could be.
A lot of the Asian bikes, up to the early '70s, used a 1-piece cast-iron oil control ring.
Then the 3-piece ring started supplanting the 1-piece ring. During that transition, our manuals covered those in detail. It *is* a better design, as many folks were breaking those 1-piece rings during install. Maybe they were introduced to help with the new EPA requirements, by putting tighter controls on oil burning and consumption, and pass smog sniffer tests.

Being a new thing, it needed to be covered in the manuals, including predictive failure, like measuring the side clearance. But, I've never heard of any side clearance failures. So, maybe that prediction doesn't happen, and now can be ignored, left out of the manuals. Dunno, a lot of that stuff is long ago, on the other side of the "proprietary wall"...