Break in Cart
- Thread starter rainman
- Start date
Compu-kart
Member
Jaguar in the background looking good Rainman!
rainman
Member
Thanks. that's my baby, for sure.
Attachments
Pete_Muller
Moderator
As an aside to this thread (and Rainman: I have zero issues with people breaking in engines, and what you've built is an ideal solution)....
After I had been in karting for a good number of years, I came to realize that "break in" was essentially "wear in". My conclusion was that if I could figure out all the things that needed to be "worn in" before an engine would really run well, maybe I could make an engine run as good as it's going to run from the first moment it's started.
It took me a while to figure out what had to be done to accomplish this (my testing was primarily on a Yamaha, because they are cheap and it's one of the classes I was racing at the time). Essentially, understanding how to ...
- distort the bore of the cylinder for honing EXACTLYl the way it's distorted on an assembled engine
- understand the shape of the piston for a given application (how much cam and how much taper)
- how the ring needed to be prepared (flatness, fit to the bore, end gap, tension)
- how to assemble the engine exactly the same every time so all the above could apply
Once I was able to predictably and consistently do the above, I was able to go to a road race and the first time the engine would start was when the green flag dropped. Zero "break-in", no need to run it rich or easy. Note that this was not accomplished by running things "loose" -- quite the contrary: I ended up running less piston clearance than I had ever run.
If there is interest in discussing this... we can start a new topic.
PM
After I had been in karting for a good number of years, I came to realize that "break in" was essentially "wear in". My conclusion was that if I could figure out all the things that needed to be "worn in" before an engine would really run well, maybe I could make an engine run as good as it's going to run from the first moment it's started.
It took me a while to figure out what had to be done to accomplish this (my testing was primarily on a Yamaha, because they are cheap and it's one of the classes I was racing at the time). Essentially, understanding how to ...
- distort the bore of the cylinder for honing EXACTLYl the way it's distorted on an assembled engine
- understand the shape of the piston for a given application (how much cam and how much taper)
- how the ring needed to be prepared (flatness, fit to the bore, end gap, tension)
- how to assemble the engine exactly the same every time so all the above could apply
Once I was able to predictably and consistently do the above, I was able to go to a road race and the first time the engine would start was when the green flag dropped. Zero "break-in", no need to run it rich or easy. Note that this was not accomplished by running things "loose" -- quite the contrary: I ended up running less piston clearance than I had ever run.
If there is interest in discussing this... we can start a new topic.
PM
moebiusgold
Member
Ramble alert. I'd be interested in a discussion for sure as modern designs, materials, surfaces finishes, lubricants..... have evolved such that most everything new consumer related doesn't seem to require a "break in" any more. So I'm a fan of what Pete has done and is proposing. Get most of the way there with the build technique and get that last little bit of wear when the thermal loading and cooling is under the same your race conditions. For most of us those conditions can only be economically achieved by racing for the break in period. A dyno cell has to get really fancy before it duplicates the real thing. The engine operating conditions while racing are not achieved at anything less than everything the same as for racing. So if break in is occurring at non race operating conditions things are loaded thermally and mechanically slightly differently so the bits and pieces will be shaped slightly different. Things like less power, RPM, less heat, or more heat (from non optimum mixture or spending less time at WOT) will cause the bore and piston profiles to be different (than the shapes under "Race" conditions) which can cause wear or sealing issues. This affects some engines more so than others btw. The right modern lubricants have made little or no break in easier to achieve too. You can get really scientific about lubricant testing and that is another can of worms....
rainman
Member
I am sure you can do it that way and is better, but that's for people with your knowledge and talent, and I am afraid I am not so talented or have acquired that knowledge and what is worse I don't have the time to try. Wish I could. Thanks for your post, there is always something to learn from your posts.
Pete_Muller
Moderator
Rainman,
It's not complicated -- there are just a few key things that make a significant difference. We can start with one item:
1 - Piston taper (or let's say: how much taper is required/ideal) is primarily determined by a few things:
> How radical the exhaust pipe is
> How heavy the kart is, and what the gear ratio is (in other words, how fast it goes through the rev range)
The more radical the exhaust pipe is, the more power is produced over a narrower rpm range (typically). More power means more heat, and more heat means the crown of the piston gets hotter, so the piston grows more at the top. Consequently, the piston really needs more taper (at least ideally).
Ditto on gear ratio and weight -- the heavier the kart is, and the taller the gear is... the slower the engine is going through the peak power range, which means, once again, more heat into the crown of the piston, so the piston needs more taper.
sidenote: The main reason for carb "triggers" (in road racing) isn't to lean the engine out at the top... it's to flood the engine with fuel through the mid-range to keep the piston alive.
An example of the extremes:
- A very light, direct-drive go kart, with a mild/wide-range exhaust pipe, and a really low gear.
- A very heavy Yamaha enduro kart, with a crazy tall gear, running at Daytona, with an exhaust pipe that puts out a ton of power over a narrow range.
The general solution is to just measure the piston, and change the clearance until the engine doesn't seize.
The problem with that approach is, in the "high load, radical pipe" setup, the typical piston has to have a lot of clearance, and that beats the crap out of the piston skirt. That causes the piston to get "barrel shaped" fairly quickly, and the more the piston rocks, the quicker the ring wears. It goes downhill quick -- the most the piston rocks, the quicker it wears even more, then rocks more, etc.. That why a "fresh" piston is usually better/faster, but doesn't last very long (probably just one 45 minute road race).
We'll continue..... if you'd like. I can dump this in a new thread if you'd prefer -- I like you're break-in cart idea, and don't want to hijack that in any way.
PM
It's not complicated -- there are just a few key things that make a significant difference. We can start with one item:
1 - Piston taper (or let's say: how much taper is required/ideal) is primarily determined by a few things:
> How radical the exhaust pipe is
> How heavy the kart is, and what the gear ratio is (in other words, how fast it goes through the rev range)
The more radical the exhaust pipe is, the more power is produced over a narrower rpm range (typically). More power means more heat, and more heat means the crown of the piston gets hotter, so the piston grows more at the top. Consequently, the piston really needs more taper (at least ideally).
Ditto on gear ratio and weight -- the heavier the kart is, and the taller the gear is... the slower the engine is going through the peak power range, which means, once again, more heat into the crown of the piston, so the piston needs more taper.
sidenote: The main reason for carb "triggers" (in road racing) isn't to lean the engine out at the top... it's to flood the engine with fuel through the mid-range to keep the piston alive.
An example of the extremes:
- A very light, direct-drive go kart, with a mild/wide-range exhaust pipe, and a really low gear.
- A very heavy Yamaha enduro kart, with a crazy tall gear, running at Daytona, with an exhaust pipe that puts out a ton of power over a narrow range.
The general solution is to just measure the piston, and change the clearance until the engine doesn't seize.
The problem with that approach is, in the "high load, radical pipe" setup, the typical piston has to have a lot of clearance, and that beats the crap out of the piston skirt. That causes the piston to get "barrel shaped" fairly quickly, and the more the piston rocks, the quicker the ring wears. It goes downhill quick -- the most the piston rocks, the quicker it wears even more, then rocks more, etc.. That why a "fresh" piston is usually better/faster, but doesn't last very long (probably just one 45 minute road race).
We'll continue..... if you'd like. I can dump this in a new thread if you'd prefer -- I like you're break-in cart idea, and don't want to hijack that in any way.
PM
rainman
Member
No problem at all. What you say makes much sense, and I certainly use the KT100s to experiment some things, since they are way cheaper. I don't take many chances with my reed 98 TSL PCRs, for example, or the rotary Ital, but I rarely have issues with them, other than changing piston when it is due. Most work with my 131 stroker Sudam is usually done by Buller, though I am planning on selling this engine torun a 250. 2 engines that have surprised me regarding reliability are my Aixro XR 50 (aka Wankel), with over 10 years without any issue at all other than some carb issues I fixed, and the 125 Modena KZ shifter I have in Europe, which is very fast and I expected it to be unreliable but it has been bullet proof.Rainman,
It's not complicated -- there are just a few key things that make a significant difference. We can start with one item:
1 - Piston taper (or let's say: how much taper is required/ideal) is primarily determined by a few things:
> How radical the exhaust pipe is
> How heavy the kart is, and what the gear ratio is (in other words, how fast it goes through the rev range)
The more radical the exhaust pipe is, the more power is produced over a narrower rpm range (typically). More power means more heat, and more heat means the crown of the piston gets hotter, so the piston grows more at the top. Consequently, the piston really needs more taper (at least ideally).
Ditto on gear ratio and weight -- the heavier the kart is, and the taller the gear is... the slower the engine is going through the peak power range, which means, once again, more heat into the crown of the piston, so the piston needs more taper.
sidenote: The main reason for carb "triggers" (in road racing) isn't to lean the engine out at the top... it's to flood the engine with fuel through the mid-range to keep the piston alive.
An example of the extremes:
- A very light, direct-drive go kart, with a mild/wide-range exhaust pipe, and a really low gear.
- A very heavy Yamaha enduro kart, with a crazy tall gear, running at Daytona, with an exhaust pipe that puts out a ton of power over a narrow range.
The general solution is to just measure the piston, and change the clearance until the engine doesn't seize.
The problem with that approach is, in the "high load, radical pipe" setup, the typical piston has to have a lot of clearance, and that beats the crap out of the piston skirt. That causes the piston to get "barrel shaped" fairly quickly, and the more the piston rocks, the quicker the ring wears. It goes downhill quick -- the most the piston rocks, the quicker it wears even more, then rocks more, etc.. That why a "fresh" piston is usually better/faster, but doesn't last very long (probably just one 45 minute road race).
We'll continue..... if you'd like. I can dump this in a new thread if you'd prefer -- I like you're break-in cart idea, and don't want to hijack that in any way.
PM