Topic: Where to position piston ring gap?

[timtune]

CB750 - Where do I position the ring gaps prior to installing the jugs?

[CycleRanger]

From page 45 of the service manual.
If you don't have a copy of the Honda 750 service manual you can get one from the link in my sig. 

[Tracksnblades1]

This is similar to an oil thread. But I’m a Chevy/Smokey Yunick Fan so the:

top ring end gap goes 12:00 to the major thrust side (not 45*off to the side but 0* major thrust)
Chevy and Smokey wants the piston ring lands to cover the top ring’s end gap when the piston is forced to the major thrust side..

Second ring 6:00 minor thrust side just the opposite 180* from top ring..

Oil ring end gaps 90* apart and facing away from crankshaft’s rotational sling oil…

Several OEM engine manufacturers used to recommend the same. The most unusual were the D50 dodge with the Mitsubishi engine.
Top and second ring gaps were both aligned…? Always wondered about that…but we’re taught that rings rotate aren’t we…?

The 180* apart will yield the best leak down tests, but the time slip is real world….
A lot has changed in performance ring gaps. The second ring used to have a smaller end gap than the top ring because it ran cooler and expanded less and was less prone to butt ends. Look at Honda’s old specs. But modern technology says to gap the second ring larger than the top ring so the second rind doesn’t trap any compression that can unload the top ring and cause top ring flutter..again the time slip is the tell tale…but everyone I know hates to see an engine that can sweep the track clean from blow-by..

Never the less, follow PEWE’s recommendations on properly preparing rings end gaps by correctly chamfering so you don’t score your cylinderswalls  regardless where your end gaps end up…😁



 

[PeWe]

Yes, chamfering the inner end corners of the oil rings (rails) make it easier to not pinch them. Sharp inner corners can hook into the expander and a ring will not compress.
I have seen new rings with small  burrs on the outer ends that could have scratched the bore.
Not low tech, Wiseco. 240-400 grit paper fixed that. Part of the installation.

From Dynoman's tech pages.
Bore size does not matter.

[timtune]

Thanks All

[willbird]

A lot has changed in performance ring gaps. The second ring used to have a smaller end gap than the top ring because it ran cooler and expanded less and was less prone to butt ends. Look at Honda’s old specs. But modern technology says to gap the second ring larger than the top ring so the second rind doesn’t trap any compression that can unload the top ring and cause top ring flutter..again the time slip is the tell tale…but everyone I know hates to see an engine that can sweep the track clean from blow-by..

The bigger gap in second ring was explained for boosted applications by a guy I watch on Youtube, he does about zero zilch nada normally aspirated stuff. There is a guy from total seal piston rings that does some pretty good videos. Lots of interesting info on his channel.

https://www.youtube.com/results?search_query=total+seal+piston+rings

[Tracksnblades1]

A lot has changed in performance ring gaps. The second ring used to have a smaller end gap than the top ring because it ran cooler and expanded less and was less prone to butt ends. Look at Honda’s old specs. But modern technology says to gap the second ring larger than the top ring so the second rind doesn’t trap any compression that can unload the top ring and cause top ring flutter..again the time slip is the tell tale…but everyone I know hates to see an engine that can sweep the track clean from blow-by..

The bigger gap in second ring was explained for boosted applications by a guy I watch on Youtube, he does about zero zilch nada normally aspirated stuff. There is a guy from total seal piston rings that does some pretty good videos. Lots of interesting info on his channel.

https://www.youtube.com/results?search_query=total+seal+piston+rings

Good vids…

It’s interesting they still push their gapless second ring. Even though it’s counter intuitive to their new tech recommendations..

I’ve ran the total seal gapless second rings with good results. I never had a top ring flutter that I knew of, but only turned them 7800…However Ive never compared them to a standard wider gapped 2nd ring in the same app either…Which total seal claim they have and there’s a hp advantage way up on top…I’m a Missouri type guy so “show me”..

I will say I’ve never seen a lower leak down test than a Yunick style prepared block with the gapless second ring..Loosen or tighten any head stud off the torque plate torque and the leak down will increase..

Yes, blown, turboed, and nitrous engines have always ran larger end gaps. They used to say if you run them too loose nobody knows, too tight everyone knows…Wiseco recommends the larger second ring gap on there stuff now regardless of boosted or NA apps…I have a new set of 71.25mm wisecos for a 750 that’s recommending the larger 2nd ring gap from a NA app too..

[willbird]

A lot has changed in performance ring gaps. The second ring used to have a smaller end gap than the top ring because it ran cooler and expanded less and was less prone to butt ends. Look at Honda’s old specs. But modern technology says to gap the second ring larger than the top ring so the second rind doesn’t trap any compression that can unload the top ring and cause top ring flutter..again the time slip is the tell tale…but everyone I know hates to see an engine that can sweep the track clean from blow-by..

The bigger gap in second ring was explained for boosted applications by a guy I watch on Youtube, he does about zero zilch nada normally aspirated stuff. There is a guy from total seal piston rings that does some pretty good videos. Lots of interesting info on his channel.

https://www.youtube.com/results?search_query=total+seal+piston+rings

Good vids…

It’s interesting they still push their gapless second ring. Even though it’s counter intuitive to their new tech recommendations..

I’ve ran the total seal gapless second rings with good results. I never had a top ring flutter that I knew of, but only turned them 7800…However Ive never compared them to a standard wider gapped 2nd ring in the same app either…Which total seal claim they have and there’s a hp advantage way up on top…I’m a Missouri type guy so “show me”..

I will say I’ve never seen a lower leak down test than a Yunick style prepared block with the gapless second ring..Loosen or tighten any head stud off the torque plate torque and the leak down will increase..

Yes, blown, turboed, and nitrous engines have always ran larger end gaps. They used to say if you run them too loose nobody knows, too tight everyone knows…Wiseco recommends the larger second ring gap on there stuff now regardless of boosted or NA apps…I have a new set of 71.25mm wisecos for a 750 that’s recommending the larger 2nd ring gap from a NA app too..

Indeed larger ring gaps when any power adder is used, but Steve Morris was quite specific about the second ring gap being larger than  first especially in boosted applications specifically to prevent a buildup of pressure between the two rings. The latest total seal video covers cylinder wall finish and skirt clearance, and some other progressive improvements that resulted in being able to pull more crankcase volume using a vacuum pump. On our engines with air cooling I have pondered what the bore size ends up at operating temp, and more important what is the piston skirt clearance when engine is at operating temp. Also if we roll into WOT does that temperature rise then stabilize ? Does the piston warm up more quickly or does the cylinder ?

The line2line sacrificial coatings look pretty cool, and can be combined with coatings on the piston dome that prevent some heat transfer. There is potential there to put a modern "perfect" finish on the bores, making them round again in the process,  then coat the stock pistons up in dia so that they self clearance when the engine is broken in. We will only gain some small % of total HP so one might never feel it seat of the pants due to our bikes being heavy and our HP sparse LOL.

Hmm picking up two flywheel HP on a 600lb bike, going from 50 to 52 might shave .15 seconds off the 1/4 mile time. So going from a high mile engine to one that was freshened up with a modern bore finish, best choice rings that will fit the stock pistons, and the Line2Line coating might be really interesting in a bike like the guy was building over in the High Performance section to run a mostly stock engine to start with.