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Discussion Starter #21
Yeah and still not able to get ahold of AZ Quads who sells the custom kit. I ended up putting it together as-is and she started right up. The added displacement and compression sure gave it some more grunt down low.
 

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Discussion Starter #22
CP didn't want to offer much more info than .028" could be okay. I asked them some further questions but they advised to ask AZ Quads instead. We'll see how it breaks in during the upcoming season. I assume I'll notice excessive blow by out of the crankcase vent as one symptom of excessive gap?
 

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I always thought CP supplied the rings with the piston when ordered. So it would be CP to make it right. UNLESS, the seller already gapped the rings and took to much off.
They do, but not always packaged with the pistons. Sometimes it’s bulk packaging with pistons seperate from rings. Seller may have grabbed wrong rings. This is still all assuming the kit was all done properly, which maybe it was.

In this specific application maybe it requires larger gap than cp general guidelines, which is what the op went off of. That is very plausible and actually likely from what I’ve learned the past couple years.
 

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They do, but not always packaged with the pistons. Sometimes it’s bulk packaging with pistons seperate from rings. Seller may have grabbed wrong rings. This is still all assuming the kit was all done properly, which maybe it was.

In this specific application maybe it requires larger gap than cp general guidelines, which is what the op went off of. That is very plausible and actually likely from what I’ve learned the past couple years.
Yep, you have a good teacher. I just thought CP would have been more helpful.
 

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So
I always thought CP supplied the rings with the piston when ordered. So it would be CP to make it right. UNLESS, the seller already gapped the rings and took to much off.
Sometimes they are packaged in bulk, with the pistons and rings seperate instead of in single retail kits. That would require whoever is doing the kits to put the correct rings and pistons together.
Also it’s entirely possible that the ring gap needs to be bigger in that application than what cp general guidelines state. These are reasons why youde need to talk to whoever designed the kit.
I say that because that’s exactly what I dealt with last year.
 

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Didn’t realize that posted first time I typed it out. Cp isn’t the greatest to deal with sometimes. For example they repeatedly produce batches of wrist pints that arrive with small nicks and scratches in them. When the issue is brought to their attention, they promptly send out more bad pins. So on and so forth without addressing the issue.
So it could still absolutely be CPs fault, entirely.
 

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Got to check everything twice. A few years back I bought a BB kit for a 250R dirt bike and it came with a standard size head gasket. The seller said it would be fine to run it. I sent it back as fast as I could. Your ring package should have a part# on it, did you look it up to make sure it was not for a 105.5 piston?
 

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Discussion Starter #28
Yeah. A 105.5 would have a much larger gap since circumference
(Gap) = pi x diameter which mean it would be +.120". I did give CP all the part numbers to cross reference as well. It wasn't until then that they figured out it was a private custom kit and sropped helping. I was hoping for a bit more support from them but I'll keep trying to get ahold of AZ Quads who sold me the kit. Funny how they replied instantly to every email and phone call up until the purchase and now nothing!
 

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Aw man that’s such a bummer to hear.
Have you tried doing a compression check on her yet while hot? I wonder if that would give you a good idea of how the gap is working out.

T web, how come you needed a gap outside of spec on the diamond piston, and how would you know if you needed to over gap one again?
 

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I run thin rings in my race car and they do not require wide clearance. For my car most of the rings butt up out of the package, they have no clearance. On bikes and quads the ring packages I have used come too tight, but have some clearance, all have required some material removal.
 

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Discussion Starter #31
I do have a compression tester but didnt do a test since the auto decompression mechanism will skew the results. Although if i had taken a baseline with the 11:1 setup, i would have had something to compare to. As far as ring thickness and gap, the top ring on the CP 11:1 102mm piston has the same 1.0mm thickness as the ring on the 12.5 106.5mm setup yet it came new at .012" and had to be opened up. Unless they mean width as the 106.5mm top ring is skinnier. I tried to ask CP this but thats when they shut down any further discussion.
 

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Thinner material gets hot faster, which means it could expand more.
They build pistons to suppliers specs. Whoever is putting the kit together is who should be responsible to ensure the parts work together.
Cylinder could be too big or not round. Supplier could’ve spec’d wrong size piston for correct wall clearance. Supplier could’ve sent wrong rings with piston. Too many variables to jump on CP for doing anything wrong.
Yes, thinner gets hotter faster, as there is less material.
But you are insinuating that less material grows larger under the same temperature.
 

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Metal also will only expand to a point at a given temperature.
So, a ring gap spec is designed to close up(or close to it) at operating temperature.
A wider gap isn't going to continue to grow until it closes and meets resistance, and shrink the ring's thickness to compensate for it.
And, in theory, if there was any measurable difference in the temperature across the entire ring(s) surface in a running engine, the coolest point would be the gap.
As the gap is not exposed to friction(other than it's outer edge), and it would be the point where heat could "escape".
 

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Aw man that’s such a bummer to hear.
Have you tried doing a compression check on her yet while hot? I wonder if that would give you a good idea of how the gap is working out.

T web, how come you needed a gap outside of spec on the diamond piston, and how would you know if you needed to over gap one again?
It’s a custom application with not very many in use, so it was a learning curve. The material used grew more than expected, went to zero gap and scored the cylinder. Rebuilt top end only change being larger gap, looked perfect when I pulled head off this time.
The experienced person selling the custom parts is who would know.
 

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Motorman
I do have a compression tester but didnt do a test since the auto decompression mechanism will skew the results. Although if i had taken a baseline with the 11:1 setup, i would have had something to compare to. As far as ring thickness and gap, the top ring on the CP 11:1 102mm piston has the same 1.0mm thickness as the ring on the 12.5 106.5mm setup yet it came new at .012" and had to be opened up. Unless they mean width as the 106.5mm top ring is skinnier. I tried to ask CP this but thats when they shut down any further discussion.

Motorman455 can you give me an update on the 745 bb. I'm looking to buy a 734 bb kit but ran across the 745. Is the 745 kit reliable
 

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Discussion Starter #36
I just got the kit and have only ridden back and forth down my road for a few 100 yards so i can't comment on durability. I did end up getting ahold of AZ Quads by calling several times and inquired about the 0.028" ring end gap on mine. As expected, they had no idea what worked but did go measure other kits they had in stock. They said those all measured around 0.018" so i guess im just unlucky. They were contacting CP to see about sending me another set of rings but never heard back from them. No surprise.
 

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I just got this same kit, looking for more feedback ? Don’t know if you’ve had enough ride time on it but would be interested in seeing how you like it. I’ll be running a +2 head with it as well
 

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Discussion Starter #38
I have only been able to put about 15 miles on the 745 due to the COVID lockdown. I also went from 11:1 to 12.5:1 at the same time. The gains feel big to me and I'm still dialing it in with autotune. Especially in the low end response amd midrange. I should have just done this when i did the porting and cam in the first place. She's gonna be a handful in the trails for sure but i put a 2 position map switch on the bars to go between mellow and aggressive. How did your ring gap end up?
 

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I just got the 745 kit from the same place and my ring gaps are about .028" too. The thin oil rings have a few thou clearance and should be .015". I'm a little hesitant to use them and this is the first time I've messed with the top end on any motor.
 

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Discussion Starter #40
Interesting. I called them about the ring gap and the guy claimed to go in back and measure a few kits and claimed they were all 0.018". I've been running it at 0.028" so far and haven't noticed any issues like blow by. Seems to be running great. However, i didn't notice the oil ring gap issue that you mentioned. If you have time, i would ask them for another ring kit and hope they fit better but I'm starting to wonder...
 
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