Piston siezure 100cc w/c Reedjet

A

arc100

Member
I'm beginning my investigation into 2 Reedjets that I mandrel honed and installed a fresh top end piston kit.

I will try and post some pics in next few days.

The weather is cold here now and during the race weekend was about 6-10 deg C.

It appears that the middle of the sides of the piston is where the seizure has tightened up on the fron and back of the piston that would indicate to tight in the clearance but it was .005" or 0.127mm.

My hone job was perfect in both cylinders and I have very accurate measuring equipment. 0.001mm micron accuracy Mitutoyo bore gauge and a 3-point internal mic to confirm measurement all with calibration rings.

Both engines were properly run in for 20 minutes and one engine lasted a heat race then the guy swapped to fresh fuel with Shell Advanced M castor oil which he mixed in in the cold late afternoon weather. Somewhere around 7-8 deg C presume. The second engine fitted to the same kart expired after half a lap of racing. Both have ignition set at 2.0mm. Everything is as per normal. And no sign of a very lean condition and next to no damage on the ring apart from the ally that was stuck to the cylinder walls passing over the ring sealing surface.

The other guy I build engines for had no problems, he was mixing his oil in a jug each time he refuelled his tank. He alerted me on day 2 of the race that he had been getting an oily slurry at the bottom of the mixing jug. He also used the same Shell castor oil.

Now I work for a chemical company and did some oil ratio tests from his fuel tank on the kart to check that the oil was not still in the 20 liter fuel drum that he had premixed 16:1 using premium grade 98 octane fuel from the local petrol station same as most other racers on the weekend.

The tests I performed in the lab are accurate and shows the correct amount of oil in the tank as it did with the fuel drum.

Can anyone help me out here. I'm lost as to what has happened. No other engines I built in the past for Mx bikes or karts have ever seized under normal use.
 
Castor and cold weather do not go together well, the castor tends to separate, I used to add some acetone for a catylist to keep them mixed, but I now use different oil.
 
One engine lasted a heat race so it must not have been a cold stick, it obviously wasn't from lack of clearance at .005, it seems to me it comes down to two possibilities assuming that the engines were sealed up good and had no intake leaks and that would be either an oil issue, which you may have already ruled out, or the carb's settings were a tick lean because of the really good air density of the cold air. How much richer were the needle settings than what you ran before the weather cooled off ? What kind of engine temps did you see before it seized? You probably won't get a good answer from the other side of the world with us just knowing you had a stick, but from your posts I'm sure you have the knowledge and technology to figure it out, let us know what you find. Jon
 
The air density had to be way up there. If you had any information on the exhaust temp, you might see a reason for the stick.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
Yeh I'm thinking oil separation too because all the seizures happened after he switched over to his new batch of fuel. Also his stock KT that he was running in another class also run really bad. His KT didn't seize but was very slow compared to how he normally runs in the KT stock class and he was running the same fresh batch of fuel. Just got me puzzled because when I tested the fuel for oil content it tested ok @ 16:1

The top of the piston and head show no signs of lean mixture. The top is not damaged at all. Even the ring looks ok. Just half way down the piston it gets a bit nasty. I haven't checked under the piston yet.

Its got me paranoid now.

Water was at 43 deg C when it happened but the other guy running my engines was @35 deg C at the start of the race and he didn't have a problem all weekend although he did tell me about the fuel oil mixing problem on day 2 of the race weekend which most likely would have saved both engines. So glad I never finished the fit-up on the Siamese twin I got off Zac Lamb or that would of been seized as well. At least I saved the twin.
 
sounds like a 4 corner stick or similar, this is a cold stick or lean mixture. when the air is good (when it's cold) and a combination of lean mixture combined sounds like your problem.. get heat in the engine, and when you have good air richen up, don't lean it out..
 
I used that oil for many years and it has actually been the oil I have been luckier with if we are talking about piston seizures. Considering the cold weather, were both engines broken in properly or for the same time/rpms before actually racing?
 
send pistons to Swain tech & have coated & never stick again ive used them for 20+ years you can lean down until it dies before it will stick i can get years out of a piston...............
 
parilla87 said:
send pistons to Swain tech & have coated & never stick again ive used them for 20+ years you can lean down until it dies before it will stick i can get years out of a piston...............
Click to expand...

Not denying you but are you serious. I can actually lean the engine so bad that it kills the engine and still not seize?

I use Vertex pistons that are already coated but I assume they are coated to a commercial level. What I mean is coated just enough for Vertex to say they are coated. Also there are a heap of different coatings. Some expensive, some not.
 
rainman said:
I used that oil for many years and it has actually been the oil I have been luckier with if we are talking about piston seizures. Considering the cold weather, were both engines broken in properly or for the same time/rpms before actually racing?
Click to expand...

Same run-in time on both engines, same procedure. The owner was running the engines in at my work.
 
I just did a fairly low tech sort of test and to me it was fairly conclusive.

It worked better with the head on.

What I did was shine an pen style LED torch into the plug hole and then look into the top of the piston and look at the reflection of the light on top of the piston.

The 2 engines that seized are like a 4 stroke. They are dry almost like matt black anodised aluminium looks. There was no shiney reflection.

The 2 Maxter wc reeds that had NO seizure problems with the same test have an oily shiney reflection.

What has me puzzled is that all the cylinder heads look the same with a bit of oily appearance and all the exhaust ports of all the engines have the usual oily residue as well. If it had no oil due to unevenly mixed fuel then I would assume the exhaust port would be dry.
 
So one kart ate two motors? Any chance of a fuel delivery problem, tank vent, plugged/pinched line etc.? Did each motor have it's own carb?
 
Neo said:
So one kart ate two motors? Any chance of a fuel delivery problem, tank vent, plugged/pinched line etc.? Did each motor have it's own carb?
Click to expand...

Yeh that's what I asked him, did you use the same carb on both engines. Answer, No. Each engine had its own carb.

I'm looking at the tank and all seems ok. The strange thing is it ran fine and strong in the first heat race. Ran fine during the 15-20min running-in phase at my work in the carpark.

He said it all started happendinhg when he changed to the fresh fuel drum. But as I said earlier I tested the fuel in the lab and the oil ratio is fine. even in the tank of the kart. Which he gave to me a few days ago.

His stock class KT ran slow too but didn't seize. Its normally pretty good.
 
You must log in or register to reply here.
Back
Top