1.01 cmb burning holes in pistons

[Tom Foley]

It seems to me the real matter at hand is if this is the powerplant we are dealt , RS - 101 , how can this engine be modified to be less of a spoiled brat like the VAC 91 which is capable of going just as fast with way less of a" re-invention of the wheel problem "

 

[Joe Warren]

It seems to me the real matter at hand is if this is the powerplant we are dealt , RS - 101 , how can this engine be modified to be less of a spoiled brat like the VAC 91 which is capable of going just as fast with way less of a" re-invention of the wheel problem "

Tom the Vac 91 does not have the power to the prop like the RS101 does. VAC 91 - you are limited to a 6.5 6.6 1667 Prop. Rs101 You can pull 7.2 - 7.5 1667 easily. I have had them both.... Maybe it is as easy as a T port? And the Brass Head Buttons allow you to Make Engine Heat and run faster on a Richer Needle.........

 

[Tom Foley]

Maybe so . All this discussion is a great thing though because unless you can look at what everyone else is doing and how they are solving problems it's hard to learn . Happy New Year guys !!

 

[Tom Foley]

As this conversation continues? a way to check your existing fuel system is set up properly? After you have gotton onto the lake and made a lap or two your fuel system should flow enough fuel to richen the boat up on a FAT Needle at High piston speed. If it cannot not? you better start to look at it. This means you cannot maintain a high piston speed & fatten the engine up too. This is going to be a Problem when you try to Run Wide Open Throttle Loaded with prop.... If you are Miling Rich and Happy And an medium increase in throttle position the engine seems to COME INTO ITS OWN NEEDLE?? STOP STOP !! ITS RUNNING OUT OF FUEL........... THIS is a Perfect example of its fixed to Burn Itself Up. This is a Must Test before you even think about leaning it down. A topic we had eariler in the week was about Reading the Plug........ I HAVE NEVER SEEN A ENGINE EAT A PISTON THAT WAS GIVING HAPPY PLUG READINGS. If this does Happen? Look for what changed?? Cracked fuel inlet line No pipe pressure or Cracked & Burnt header orings..... Normally the Glow plug would have been already Warning the driver that something was wrong with the boat!!

This is good info and this is what I look for everytime the boat comes back alive .Feel the engine temp , look at the plug ,look at and clean the fuel filter , look at the fuel and pressure lines . Maybe the 101 engine is sending signals that have to be carefully observed and corrected for . It's amazing at the difference between the 91 and 101 in terms of tuning acuity .

 

[SayMikey]

One thing for sure when she blows a hole you know right away. Sounds like a fart. A $200 one

 

[Joe Warren]

looks like there is soon going to be a CMB RS/EVO 91 according to Ians web site. Whatever that is?????

 

[Mark Bullard]

I have been watching this all day. Joe is dead on with the reason that you can hole a 101. I have never holed a RS 91 but the RS 91 does not move the fuel that the RS 101 does. The RS 101 will turn more rpm than the RS 91 or VAC 91. The reason is the RS 101 is over square or it's bore is larger than it's stroke. So this mean more rpm. This makes a cooler running engine by moving more fuel and air thru the motor. So you must get the temp up on this motor. And if you crank the needle down or cut the water off to build heat you will cut the motors fuel off or build heat that you can not control and it will then hole a piston if you allow it to. On the Turkey Day Record Trial on post 60 you will find three straight away passes with my twin. The day before I set the oval record with a heat racing setup just the way the boat was set from the last heat in Charleston. The boat ran 86 to 88 on many straight away passes with this setup and this is thru the traps. And of course we all know what the record is now. For the next day the only changes I made in the boat was to install a couple props that I had setup for the day. The record and recorded passes were on 50% fuel, 0.530 bore carbs, 189 exhaust, 130 boost and transfer, 64 degrees after TC with a total open duration of 212 degrees, my brass head buttons set a 0.010" on Octure 1667s. If you watch this video you notice that the rpm is up there but not like it was for the record. The props were Octure 2267s on the straight away passes and I was at the back door on 100mph. If I knew how to post the video on this post I would.

 

[Tim_Duggan]

Any relevance at all?

http://gallery.intlw...pos=235&uid=141

My RS101 is still in the box waiting for me to build the boat, so I don't have any personal experience with this piston issue. Please ignore if deemed completely irrelevant!

Also, are there better O-rings for the CMB header than the originals?

 

[dwilfong]

Any relevance at all?

http://gallery.intlw...pos=235&uid=141

YEP!!!!!

My RS101 is still in the box waiting for me to build the boat, so I don't have any personal experience with this piston issue. Please ignore if deemed completely irrelevant!

Also, are there better O-rings for the CMB header than the originals?

 

[julianconde]

good find very relevant

 

[dwilfong]

 

[dr gary turner]

Any relevance at all?

http://gallery.intlw...pos=235&uid=141

YEP!!!!!

My RS101 is still in the box waiting for me to build the boat, so I don't have any personal experience with this piston issue. Please ignore if deemed completely irrelevant!

Also, are there better O-rings for the CMB header than the originals?

So was the result of the angle change due to increased cross sectional area or redirection of the intake fuel flow going more across the piston for cooling instead of up into the combustion chamber?

I have thought cutting a window in the piston and sleeve would help cool the underside of the piston and decrease the chance of burning a hole, but it is a pain to do.

I have ran the 101's since they came out. After going to brass head button and getting the needle away from the carb, ie more fuel like a surge tank, no holes. Previously holes were from lean runs, motor sounded rich all of the time and turn the "NOB" got the motor to sound better for about 1/2 lap and a burned hole in the piston. BTW we have been running brass headbuttons for 3 yrs in the 101,s.

 

[dwilfong]

Make the top of the port flat and change the angle to intersect at the middle of the piston.

This is a band aid to the problem.

 

[julianconde]

david let us know how it runs and what results you have

 

[stan simpson iv]

Make the top of the port flat and change the angle to intersect at the middle of the piston.

This is a band aid to the problem.

Ta Daa...but at least it works. Good work David,good to see you are not sitting on your bottom side.

 

[RodneyPierce]

I have been watching this all day. Joe is dead on with the reason that you can hole a 101. I have never holed a RS 91 but the RS 91 does not move the fuel that the RS 101 does. The RS 101 will turn more rpm than the RS 91 or VAC 91. The reason is the RS 101 is over square or it's bore is larger than it's stroke. So this mean more rpm. This makes a cooler running engine by moving more fuel and air thru the motor. So you must get the temp up on this motor. And if you crank the needle down or cut the water off to build heat you will cut the motors fuel off or build heat that you can not control and it will then hole a piston if you allow it to. On the Turkey Day Record Trial on post 60 you will find three straight away passes with my twin. The day before I set the oval record with a heat racing setup just the way the boat was set from the last heat in Charleston. The boat ran 86 to 88 on many straight away passes with this setup and this is thru the traps. And of course we all know what the record is now. For the next day the only changes I made in the boat was to install a couple props that I had setup for the day. The record and recorded passes were on 50% fuel, 0.530 bore carbs, 189 exhaust, 130 boost and transfer, 64 degrees after TC with a total open duration of 212 degrees, my brass head buttons set a 0.010" on Octure 1667s. If you watch this video you notice that the rpm is up there but not like it was for the record. The props were Octure 2267s on the straight away passes and I was at the back door on 100mph. If I knew how to post the video on this post I would.

This one?

 

[stan simpson iv]

I have been watching this all day. Joe is dead on with the reason that you can hole a 101. I have never holed a RS 91 but the RS 91 does not move the fuel that the RS 101 does. The RS 101 will turn more rpm than the RS 91 or VAC 91. The reason is the RS 101 is over square or it's bore is larger than it's stroke. So this mean more rpm. This makes a cooler running engine by moving more fuel and air thru the motor. So you must get the temp up on this motor. And if you crank the needle down or cut the water off to build heat you will cut the motors fuel off or build heat that you can not control and it will then hole a piston if you allow it to. On the Turkey Day Record Trial on post 60 you will find three straight away passes with my twin. The day before I set the oval record with a heat racing setup just the way the boat was set from the last heat in Charleston. The boat ran 86 to 88 on many straight away passes with this setup and this is thru the traps. And of course we all know what the record is now. For the next day the only changes I made in the boat was to install a couple props that I had setup for the day. The record and recorded passes were on 50% fuel, 0.530 bore carbs, 189 exhaust, 130 boost and transfer, 64 degrees after TC with a total open duration of 212 degrees, my brass head buttons set a 0.010" on Octure 1667s. If you watch this video you notice that the rpm is up there but not like it was for the record. The props were Octure 2267s on the straight away passes and I was at the back door on 100mph. If I knew how to post the video on this post I would.

This one?

http://www.youtube.com/watch?v=IhO6fyNs-is&list=PL5DjBE9c-zSkApUVofU1Umr1o5EFuIn2J&index=10

SWEET!!!

 

[dr gary turner]

Make the top of the port flat and change the angle to intersect at the middle of the piston.

This is a band aid to the problem.

Have you tried piston porting the piston and sleeve?

 

[Buckshot]

No secret.....

http://www.intlwaters.com/index.php?showtopic=54523#entry514446

a lot of guys have been doing it for a while.

As well as flat roof int. ports.

 

[Tim_Duggan]

So was the result of the angle change due to increased cross sectional area or redirection of the intake fuel flow going more across the piston for cooling instead of up into the combustion chamber?

Good question, one I've pondered myself! Unless one has the ability to make a sleeve from scratch or has the ability to accurately map the port T/A's, it's a bit hard to know for certain.

I have thought cutting a window in the piston and sleeve would help cool the underside of the piston and decrease the chance of burning a hole, but it is a pain to do.

I had a conversation with a well known pylon racing engine builder about this subject, and he suggested it wasn't worth the effort and adds other factors into the equation. I'm not saying that is the case or not - I'm just repeating what he said was his opinion. I have not been able to find anything to prove / disprove that piston ports make any significant difference to the temp of the piston crown and if there was a variance, how much is attributed to less friction due to less contacting surface area between the piston and the sleeve? One thng it would do is make an already fragile piston even more so by introducing extra points where a failure could occurr.