Piston siezure 100cc w/c Reedjet

Just at first glance the reed jet is too clean no carbon or burnt oil residue. The maxter piston looks like it should, the reed either leaned out or didnt have enought oil. Suprised it wasnt bunt on top by the exhaust. Which tells me it almost has to be a lack of lub problem not leaned out. I have never used the oil your using so dont know anything bout it, but i would be questing it if the ratio was 16-1 thats very high. Keep us posted on what you discover
 
Pete_Muller said:
What was the temperature in the shop when you honed the cylinders? (and measured the clearance)
Click to expand...

Yeh I was thinking about that but don't forget everything was at the same temp when I was honing. Shop temp was 12-15 deg C.

I checked it against the maxter the next day after the honing was done and they were pretty close to the same clearance. The Maxter was actually about .0005 thou tighter than the Reedjet. And the Maxter also started the racing colder than the Reedjet by about 5 deg C. Maxter at the green was 35C and Reedjet was 40C.

Here's a pic of my hone.

http://imageshack.com/a/img836/6413/fme0.jpg
 
Do you check the shape and taper of every piston you install?

Many people assume that all pistons are created equal -- grab one out of the box, measure the largest spot at the skirt 90° to the wristpin, and set the clearance.

Unfortunately, there is very much more to it than that. Pistons are cam-shaped and tapered as you know, however it's not unusual for pistons of the same size and from the same manufacturer to have subtle differences in shape.

As an example, a piston could *easily* have .001" less taper than an "identical" counterpart, but will go un-noticed by 999 out of 1000 people. That piston with slightly less taper will somewhat "act" like it has .001" less clearance. (after all, pistons never seize at the end of the skirt... the typical point of measurement).

Understanding how the subtleties of piston tolerance variations effect performance, reliability and setup are quite important (arguably one of the most important and overlooked items in the engine).

As food for thought -- required piston shape is absolutely related to the exhaust pipe. (I'll let you think about that one). :)

"Never assume...! "

Pete
 
Pete_Muller said:
Do you check the shape and taper of every piston you install?

Many people assume that all pistons are created equal -- grab one out of the box, measure the largest spot at the skirt 90° to the wristpin, and set the clearance.

Unfortunately, there is very much more to it than that. Pistons are cam-shaped and tapered as you know, however it's not unusual for pistons of the same size and from the same manufacturer to have subtle differences in shape.

As an example, a piston could *easily* have .001" less taper than an "identical" counterpart, but will go un-noticed by 999 out of 1000 people. That piston with slightly less taper will somewhat "act" like it has .001" less clearance. (after all, pistons never seize at the end of the skirt... the typical point of measurement).

Understanding how the subtleties of piston tolerance variations effect performance, reliability and setup are quite important (arguably one of the most important and overlooked items in the engine).

As food for thought -- required piston shape is absolutely related to the exhaust pipe. (I'll let you think about that one). :)

"Never assume...! "

Pete
Click to expand...

Thanks Pete. I assume you mean the pipe holding more heat closer to the piston in regards to piston expansion.

When I measured the piston for clearance I did notice that the taper didn't really start from the bottom of the skirt. It was almost parallel to the wrist-pin area and then tapered in a bit more progressively.

FWIW, it was basically a 4 corner stick on both engines. I'm going to the dyno with fresh top ends next week using the same pistons, so I'll let you know.
 
I've found that pipes that produce a big spike of peak torque (heat), like what we run in the U.S., require more piston taper. The crown of the piston simply gets hotter than a "mild" tuned pipe (ala direct drive).

In this country, we have a bit of a "historically-driven" problem in that piston shapes were evolved many, many years ago when exhaust pipes generally had a milder state of tune. IMO, the shape of pistons has not evolved along with exhaust pipe technology.

To put his into very simple terms: if it's necessary to run .004" or .005" piston clearance in order to prevent a seizure, then the shape of the piston is not correct. Period.

Pete
 
Many years ago, when I raced Mc's, I was trying to break in a Mc on the track. I really wasn't pressing down hard and it stuck. I was scratching my head. The next week I rebuilt the engine, went to the track, same thing all over again.

I'm thinking, something is wrong. I pull a fresh piston, mic the skirt than the top. The taper was the wrong way. I had a whole batch of bad Pistons. Problem solved. I learned my lessons; never take anything for granted, mic the whole piston.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
As I mentioned brfore, a 4 corner stick is always indicative of a cold stick/lean condition, with the excellent cooling of the wet engine, and the good air, the lean condition got heat into the piston which expanded faster than the steel liner.. on my wet engines I normally start out with only one duct tape width of rad. showing if any, we don't run on a sprint track with a lap or two of warm up, so where firing one lap after leaving the grid, not much time to get heat into a wet engine.. I also overdrive my pump.
 
azrcr said:
As I mentioned brfore, a 4 corner stick is always indicative of a cold stick/lean condition, with the excellent cooling of the wet engine, and the good air, the lean condition got heat into the piston which expanded faster than the steel liner.. on my wet engines I normally start out with only one duct tape width of rad. showing if any, we don't run on a sprint track with a lap or two of warm up, so where firing one lap after leaving the grid, not much time to get heat into a wet engine.. I also overdrive my pump.
Click to expand...

When you have a lean stick with no detonation does the top of the piston appear dry with a black anodized look?

Just find it hard to believe at .012 thou it was a cold stick when the 2 maxters from the other guy that I modified the port timing for was starting the races at 35C and wasn't having any problems. He was a bit lighter and had less rear drive so maybe that was enough to reduce some fast heat soak.

Probably worth mentioning that the maxters were running cold egt at 460-480C while the reedjets were at 550C when they grabbed. Perhaps that explains why the Maxters had no problems.
 
azrcr said:
As I mentioned brfore, a 4 corner stick is always indicative of a cold stick/lean condition, with the excellent cooling of the wet engine, and the good air, the lean condition got heat into the piston which expanded faster than the steel liner.. on my wet engines I normally start out with only one duct tape width of rad. showing if any, we don't run on a sprint track with a lap or two of warm up, so where firing one lap after leaving the grid, not much time to get heat into a wet engine.. I also overdrive my pump.
Click to expand...

This is very true. I have my dad's water cooled K30 engine and a few years back we ran it at Daytona. Made it about 2 laps on the dirt track and it stuck. Pulled it apart to find out that it was a cold stick. I am now working on the resolution to the problem. Maybe less water flow or less air. That day it was about 40* F the morning it stuck. I had the rad completely covered but still stuck. I believe piston clearance was 6 thou. Now working to figure problem out. Engine works good in FL on hot days but it doesn't like cold days.

Frankie
 
Can you verify that the fuel was PULP? It's telling that the issue occurred when the fuel supply was changed, maybe he accidentally filled from the wrong bowser and got some e10? In any case, pump fuel is often all over the place when it comes to burn rate, and can play havoc with ignition timing settings.
 
the 2nd engine was also warmed up prior to racing and from memory started the race at around 50deg with the radiator taped up as first thoughts was a cold seize.
egt on the first engine never exceeded 600degC (in first race and plug had no indication of being lean) and was under 550degC when it blew in the 2nd heat first carby was a l2 on what should normaly be a slightly rich setting with 1 1/4Low 1 1/4 high and 1/2 on 3rd jet and plug check after first race confirmed this
2nd engine was running a beroni carb that had been used 3 weeks earlyer on a differant engine which had no issues at the settings used but was warmer but under 20degC but egt from memory had only reached 500DegCor maybe a touch under it
 
arc100 said:
Probably worth mentioning that the maxters were running cold egt at 460-480C while the reedjets were at 550C when they grabbed. Perhaps that explains why the Maxters had no problems.
Click to expand...
550 seems really low, 1022f. It's possible, just a guess, that the engine was lean. If it was, that would explain the low EGT.

One of the things people need to learn is that a low EGT can mean two things. It could be low because of being rich, or being lean. Both are possible. Another thing people need to learn is, on the low-end, the EGT is going to be lower than on the top. A two cycle builds more heat and pressure at peak torque than at the top end. This means you have to run richer to hold down the detonation. Detonation is caused by excessive heat and/or pressure. Whenever we saw the EGT go down, or not reach its peak, we would always enrichen the mixture first. If it went down further, that would tell us we were rich. If it went up, that would tell us we had been lean. Tuning with the EGT is a lot easier with the WB3 than with a fixed jet carb. But even with a fixed jet carb, if you have an air density gauge, things are a little easier.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
alvin l nunley said:
550 seems really low, 1022f. It's possible, just a guess, that the engine was lean. If it was, that would explain the low EGT.

One of the things people need to learn is that a low EGT can mean two things. It could be low because of being rich, or being lean. Both are possible. Another thing people need to learn is, on the low-end, the EGT is going to be lower than on the top. A two cycle builds more heat and pressure at peak torque than at the top end. This means you have to run richer to hold down the detonation. Detonation is caused by excessive heat and/or pressure. Whenever we saw the EGT go down, or not reach its peak, we would always enrichen the mixture first. If it went down further, that would tell us we were rich. If it went up, that would tell us we had been lean. Tuning with the EGT is a lot easier with the WB3 than with a fixed jet carb. But even with a fixed jet carb, if you have an air density gauge, things are a little easier.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
Click to expand...


Thanks for the info Al but I think you realise that I know when a low egt can mean lean or rich mixture. Its not my kart and I haven't seen any data logging info to support an egt going cold (I haven't seen any data logging at all) after peaking egt during the acceleration pull. Maybe it was. It seems that way.

Also on dirt ovals its very difficult to watch the egt as the short straights go by in what feels like a blink. That's why I always datalog my own stuff and look at it on a laptop after the race. And I always advise that others do the same.

IDK, I always run on the richer side with my own engines. I never see the point in sticking an engine when the gains are very little running so close to the edge and also ends your race.
 
As I mentioned earlier, a 4 corner stick is indicative of a cold/lean stick., checking plug burn without doing a plug chop, is really not a good indicator.. also different engines have different pumping capability's and setups so comparing them isn't always good either..

On my wet engines, I only run one width of duct tape open on the rad., till I get heat in the engine., I also overdrive my pump so the coolant doesn't stay in the rad as long..

If you can get the data, I bet you find your egt went up and was on the way down.. with a lean condition, the piston doesn't get enough incoming cooling charge to cool bottom of piston. (hence the cold stick)

You see this alot in the spring and fall..
 
will hoefully have the data off it this weekend if the bloddy thing plays ball
pump is overdriven as well
i more go off the egt rather then the plug but check the plug for just incase as well
 
FWIW, a few yrs. back I found that my Sudams would stick real easy if the C.C. in the head were less than around 12.5, then Augusto told me that where he lives a Sudam comes with 2 head gaskets, 1 for sea level and the other for altitude. Think "Denver Heads" for the old Ford flatheads.
 
jack burroughs said:
FWIW, a few yrs. back I found that my Sudams would stick real easy if the C.C. in the head were less than around 12.5, then Augusto told me that where he lives a Sudam comes with 2 head gaskets, 1 for sea level and the other for altitude. Think "Denver Heads" for the old Ford flatheads.
Click to expand...

I always run 8.0-8.5cc in the head. Have done so for years. The Maxter was 8.0cc and so was the Reedjet. All engines running PVL and 2.0mm and one Reedjet running Selettra. Maxters were fine Reedjets stuck. FWIW I run 8.3cc in my ARC 100cc piston port watercooled, have done for years as well. Never have any problems. This is all on pump premium 98 RON petrol/gas no ethanol.
 
You must log in or register to reply here.
Back
Top