300rr topend

[GMP]

That difference in size is so small it's beyond the scope of the tools most guys and average shops have. I have some very accurate calibrated tools available to me and even then it's very technique dependent and varies with temperature. I'm just sticking with the Beta piston to retain the excellent balance of my particular motor if for no other reason.

[Hammer]

That difference in size is so small it's beyond the scope of the tools most guys and average shops have. I have some very accurate calibrated tools available to me and even then it's very technique dependent and varies with temperature. I'm just sticking with the Beta piston to retain the excellent balance of my particular motor if for no other reason.

+1 I have a big bucks bore gauge and it's all in the hand that holds it. BTW I install one size up piston at with no issue.

[GMP]

That difference in size is so small it's beyond the scope of the tools most guys and average shops have. I have some very accurate calibrated tools available to me and even then it's very technique dependent and varies with temperature. I'm just sticking with the Beta piston to retain the excellent balance of my particular motor if for no other reason.

+1 I have a big bucks bore gauge and it's all in the hand that holds it. BTW I install one size up piston at with no issue.

That's the plan. After many times measuring with said expensive tools it's still inconclusive in many cases and a safe bet to just go up size on a used cylinder. It cracks me up when I see guys trying to measure parts with cheap Chineese Harbor Freight tools .

[GMP]

OK here it is at 180 hrs. Looks half its age. Lots of oil coating all the parts. All I did was wipe the head with a rag, no BS. Ports clean and PV free. This is at 36:1 premix. Reeds surprised me, like new. Most VForce I'm had before were done with frayed and chipped edges at 75-100 hrs.

[twowheels]

Glenn: That thing looks fantastic! Good jetting and good lubrication, along with keeping the air filter clean help, and it looks like it could go another 180 hours.

If you do the math and make some reasonable assumptions, your piston has likely been up and down in that bore about 20 million times (I jest, but still). The underlying design is obviously solid.

[Jbeta300]

How long can you run a bottom end on these bikes without worrying?

[ian-cpt]

Glenn - do you remember what jetting changes you made bringing the mix down to 36:1?

[GMP]

Glenn - do you remember what jetting changes you made bringing the mix down to 36:1?

None, it means almost nothing if you do the math. Been running 36:1 in my bikes for 20 years for various reasons like sharing fuel with minis and cutting 50/50 with straight gas for a trials bike motor. As you can see, the myth about too much oil and fouling of components is bullshit. Most modern synthetic oils don't burn and go out the exhaust, why you get spooge from a spark arrestor. I just put the PV system back into the cyl last night and all it took to clean was a rag with contact cleaner. Its all in the jetting and how the motor is set up. Squish on this motor measured 1.87mm, a bit large by conventional wisdom but its obvious the burn in excellent with the current jetting.

[otpipe]

Glenn - do you remember what jetting changes you made bringing the mix down to 36:1?

None, it means almost nothing if you do the math. Been running 36:1 in my bikes for 20 years for various reasons like sharing fuel with minis and cutting 50/50 with straight gas for a trials bike motor. As you can see, the myth about too much oil and fouling of components is bullshit. Most modern synthetic oils don't burn and go out the exhaust, why you get spooge from a spark arrestor. I just put the PV system back into the cyl last night and all it took to clean was a rag with contact cleaner. Its all in the jetting and how the motor is set up. Squish on this motor measured 1.87mm, a bit large by conventional wisdom but its obvious the burn in excellent with the current jetting.

Educate me. Does cutting 32:1premix 50/50 with gas make it 64:1? Does that work on any premix ratio doubling it?
I'm outta coffee and my brain is not spooled up yet.

[DirtDogger300]

Educate me. Does cutting 32:1premix 50/50 with gas make it 64:1? Does that work on any premix ratio doubling it?
I'm outta coffee and my brain is not spooled up yet.

Technically no, but for normal mixing ratios (32:1 to 60:1 on avg.) that we use on dirt bikes the difference isn't significant enough to matter.

Remember the total volume of premixed gas would be 33 parts in this case where only 1 of those parts is oil. So if we add 33 parts of new gas thus doubling the total original volume to the already mixed gas we end up with 66 total parts where 1 of those parts is still oil giving us a ratio of 65 parts gas to 1 part oil (65:1).

Another way of looking at it is taking some originally quantity of gas mixed at n:1, cutting this volume exactly in half and adding the same amount in unmixed gas yielding the same results.

In either case:
For gas premixed 32:1 mixed 50/50 with unmixed gas: new mix ratio 65:1
For... 40:1... new mix ratio = 81:1
For... 50:1... new mix ratio = 101:1
For... 60:1... new mix ratio = 121:1

An equation expressed to determine this (doubling the original volume by adding unmixed gas):

Where an original mix ratio expressed as n : 1 (parts gas : parts oil)

New mix ratio = 2*n + 1 : 1

Ex. 32:1 originally mixed 50/50 straight gas:
[2(32)+1]: 1 = (64 + 1) : 1 = 65 : 1