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View Full Version : Could I have a bad barrel?



HONDARACER
03-16-2009, 10:19 AM
I have 2 2009 RS125 with different serial numbers. THey are quite a few numbers apart actually. One of the bikes seems to have more power than the other. The one I am riding at the moment seems to just plain lack power and has since day 1. When the engine revs to the point of where the PV opens, one of the bikes doesnt seem to care while the other seems to take off like a scared rabbit. You can hear it in the exhaust as well when the PV opens the motor changes tune and gets a ringy noise. I had to install a LED on my bike to let me know the PV is actually open.

First thing I am going to do is inspect the casting numbers and production dates cast and stamped into the barrels and will report back with my findings. There is a lot of talk on the Karting forums about differences in barrels and hao Rotax actually recalled all the 2008 engines and are replacing the barrels with new CNC machined 2009 barrels.

Hearing this I seriously think I may have a pour quality barrely. Perhaps some adjusting or tweaking can fix it?

Micah / AF1 Racing
03-16-2009, 10:37 AM
Start with taking a compression measure of each cylinder, if one is radically different it makes sense to look deeper.

kanerdog1x1
03-16-2009, 02:30 PM
at what rpm do you get the 'ringy' noise, at w/o throttle i presume?

PJ ENGINEERING
03-16-2009, 05:38 PM
First thing I am going to do is inspect the casting numbers and production dates cast and stamped into the barrels and will report back with my findings. There is a lot of talk on the Karting forums about differences in barrels and hao Rotax actually recalled all the 2008 engines and are replacing the barrels with new CNC machined 2009 barrels.

Hearing this I seriously think I may have a pour quality barrely. Perhaps some adjusting or tweaking can fix it?

The Rotax kart engine is not the same as the one in your RS125 :rolleyes: so dont waste your time with that one.

HONDARACER
03-16-2009, 05:48 PM
I realise the motors are not identical, but I am suggesting there is a possability I have a bad casting!!!

Micah / AF1 Racing
03-16-2009, 06:21 PM
Bad in what way? Honest question? Out of round or excessive piston to bore clearance will show up in a compression test, for horribly cut ports you need to remove the head and take a look. I think your casting is probably fine. While I do not have piles of experience with the Rotax 122 engine I do have a few hours of two stroke time behind me and I suspect there are other issues at play.

Please, a compression test will let us all know where your bike is at on a baseline compared to others, while you are there measure the squish clearance and report that as well, with this little bit of information a lof of things can be considered.

I too now have had a few of the new bikes on the dyno and over the years even here in the USA I have managed to own at one time or another 3 old model bikes. Yes, there is a difference in how each one runs on the dyno and the seat of the pants but, most of these differences are down to carburetion or timing or squish setting or fuel type...etc.

I have only seen one Rotax 122 assembled incorrectly from Rotax and in that case it was the lower of the two compression rings that was not completely located on the locating pin, causing a seizure. That was well over a year ago, one of the bikes Steve and I set up for the delaer only track day in Houston. Anything is possible, a compression test is step one, squish measurement is step two.

HONDARACER
03-16-2009, 07:28 PM
I did a compression test for future refernce in case of problems. It is 130ish if my gauge is reading correctly.

All I am considering is there may be difference cores used to cast the barrels and core shifting and wear can occur. As well as the cores get older the tollerances can increase. I have 3 spare barrels and have been measuring port heights from the top surface and have found what I consider to be a large variation. I may document the differences.

HONDARACER
03-16-2009, 07:29 PM
Also I know the rings are fine because I inspected them when I installed the pipe and reed valve.

FUERA.....1
03-17-2009, 12:13 AM
The Rotax kart engine is not the same as the one in your RS125 :rolleyes: so dont waste your time with that one.

I was under the impression the barrel was identical to the the rotax fr125 max kart engine but everything else was diffferent?

FUERA.....1
03-17-2009, 12:26 AM
I did a compression test for future refernce in case of problems. It is 130ish if my gauge is reading correctly.

All I am considering is there may be difference cores used to cast the barrels and core shifting and wear can occur. As well as the cores get older the tollerances can increase. I have 3 spare barrels and have been measuring port heights from the top surface and have found what I consider to be a large variation. I may document the differences.

I believe u would have found massive differences in the barrel with the port heights. Im an ex karter and now play around with motorbikes instead, we used to have massive issues with the rotax barrels. You could buy 10 engines and only 1 or 2 of them would measure up to be a competitive race engine...

PJ ENGINEERING
03-17-2009, 05:14 AM
I was under the impression the barrel was identical to the the rotax fr125 max kart engine but everything else was diffferent?

Totally different. The FR125 cylinder is around 10mm shorter and the porting is vastly different, you got to remember that the RS125 has 6 gears to keep it in the power band V the Rotax Max that has no gears!

PJ ENGINEERING
03-17-2009, 05:16 AM
Also I know the rings are fine because I inspected them when I installed the pipe and reed valve.

So you have only "looked" though the Ex and the in let port ? if so how do you know they are fine ?

You will need to remove the cylinder and check the end gap and also look the surface of the ring to check them right.

Micah / AF1 Racing
03-17-2009, 08:57 AM
I was waiting patiently for someone else to say it, thank you PJ.

HONDARACER
03-17-2009, 09:30 AM
Theres no scoring in the cylinder and the rings are still free. The problem was there from day 1 [maybe should have been caught on the PDI road test?] But with 130 compression and excellent starting I doubt the rings could have any issues.

HONDARACER
03-17-2009, 09:30 AM
Oh and the engine has 1300kms on it now. If it had a buggered ring it should have done some damage by now.

HONDARACER
03-17-2009, 09:33 AM
I believe u would have found massive differences in the barrel with the port heights. Im an ex karter and now play around with motorbikes instead, we used to have massive issues with the rotax barrels. You could buy 10 engines and only 1 or 2 of them would measure up to be a competitive race engine...

So did you ever figure out what made a "competetive" engine? A particular port height , size or shape?

FUERA.....1
03-18-2009, 12:42 AM
A competetive engine relies on certain port heights in the barrel, in relation to the angle/degrees that certain ports are opening