Airsal T6 Detonation

Areomyst

Areomyst

Scootin' America!
I know a lot of people on the forums work in the scooter industry... Has anyone had excessive detonation problems lately out of Airsal's air cooled cylinder for Minarelli H? Part number is 011337476. Plug range is correct, carb jetting is perfect, engine pressure tests fine, everything's right, and still detonates. US distributor recomended 30 thousanths squish clearance saying any less is prone to detonate. I set it at 40. I am going to take an engine home with the cylinder kit and completely measure it, figure exact displacement of the engine and corrected and uncorrected compression ratio, and I will likely post the results.

I'm suspecting that for some reason the recent batch has perhasps taller pistons or shorter heads or something... I've used this kit before without any trouble, and I've been doing this for a little while now ;)

Fuel being used is 93-94 octane... should be way more than enough for an entry level cylinder kit.
 
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So you are saying that your squish is .3mm? That';s really tight. With AC cylinders and 93-94 octane I would set it on ,7/,8 Then you will be on the safe side for sure.
 
Aloha, it seems his squish is a bit loose. .030 thousand=.75mm and .040 is 1mm. A small air leak may be causing the problem.

frank.
 
adas said:
Aloha, it seems his squish is a bit loose. .030 thousand=.75mm and .040 is 1mm. A small air leak may be causing the problem.

frank.
Click to expand...

Engine holds pressure just fine though, I'm a little lost on these... I don't know what the compression ratio is with this kit, but I'm planning on measuring it. Has anyone else has seen these issues with this particular kit?
 
Went and googled it real quick:

.30 inch = 7.62 millimeters, so I'm right between your reccomended squish for this setup Big B. :) The detonation has happened like this on a couple of different bikes w/ same kit, one using arreche carb, one using Delorto by Athena.
 
Just a sidenote, the bikes performed VERY well before they started acting up. Front wheel raised up very easily on both instances. And to think I was worried about the stock crankshafts! :p I may post photos of the pistons, but I'm short on time today, so it will probably have to wait.
 
Areomyst,
The Minarelli a/c single ring T6 should be 145-150 psi. Do they have a lot of MBTE or TAME mixed into your fuel there? Steve told me once that a high concentration of those additives can wreak havoc on the air-cooled cylinders. Spring and fall fuel formulations in the midwest are not exactly 2-stroke friendly, lol. Your octane is plenty high enough, that's not a problem.

scootertrog
 
scootertrog said:
Areomyst,
The Minarelli a/c single ring T6 should be 145-150 psi. Do they have a lot of MBTE or TAME mixed into your fuel there? Steve told me once that a high concentration of those additives can wreak havoc on the air-cooled cylinders. Spring and fall fuel formulations in the midwest are not exactly 2-stroke friendly, lol. Your octane is plenty high enough, that's not a problem.

scootertrog
Click to expand...

I honestly have no idea about the fuel additives in my area. I suppose I should do a little looking into that. I'm using the double ring kit. I've never had a problem with the single ringed one.

After considering it further, the cylinder deck height and piston length should not affect the engine like this even if it was manufactured out of spec, because I've set the squish properly anyway, so I guess I can scratch that theory.

@ Big B NRG: The squish band is pretty wide on this top end, I will try and post a photo tomorrow. How do you mean 'crappy squish band'? I suppose if it's too much I can increase the size of the dome by machining it out a little? I don't want to do that though untill I get proper measurements, which I wasn't able to do this weekend. Had to do some plumbing work under the house instead!
 
check for a air leak. I think it is running lean. Run with your choke 1/2 on to see if it makes a difference. frank
 
Areomyst said:
I honestly have no idea about the fuel additives in my area. I suppose I should do a little looking into that. I'm using the double ring kit. I've never had a problem with the single ringed one.

After considering it further, the cylinder deck height and piston length should not affect the engine like this even if it was manufactured out of spec, because I've set the squish properly anyway, so I guess I can scratch that theory.

@ Big B NRG: The squish band is pretty wide on this top end, I will try and post a photo tomorrow. How do you mean 'crappy squish band'? I suppose if it's too much I can increase the size of the dome by machining it out a little? I don't want to do that though untill I get proper measurements, which I wasn't able to do this weekend. Had to do some plumbing work under the house instead!
Click to expand...

Hmm, post a pic, makes it easier to tell, from what I'm seeing.
 
The double ring kit is set up differently than the single ring kit. Ports , piston skirt length, pin heights etc. Piston is even heavier. It will still bolt onto the minny engine and run. But.... It's different then the standard T-6 your used to getting.
Thin rings on your double ring piston right? If so this is referred to as the "Bottom End" kit, power band wise. Not Quality.
 
Areomyst said:
I'll try and get a pic to you tomorrow.

PS, do they have mental therapy for scootertuning.net addicts who have gone through three days of withdrawl?
Click to expand...

It's really amazing how many people 'love' this forum, if you could only read the Use&Abuse forumpart ;)
 
heres what you do, and this is commen in AC yamaha/ minirelli engines. I worked on 100s of bores and easiest cheapest and safest fix is to do this.
Run 2 base gaskets, meaning, use the one that came in the kit, and keep the stock one on as well. This will give you enough clearence to prevent detonation. You wont have to run high octane gas or do an special tuning and lost power as a result. Just do that, and maybe i suggest putting your Carb needle on the richest setting to allow more fuel when you slack off after full throttle.
ALso if you dont do that, and you plann on running that bore for sometime ona stock crank, the upper rod will fail with in a few 100 miles from where. What brand of bike did you say its on?
 
Do you have any idea of the max. temp. of the cylinder? When air cooled cylinders reach the 190 degrees (Celcius ofcourse) it's getting very critical, with detonation as a consequence.

If you're squish is 0,6+mm then this is not the problem. The only reason I can think of is a very lean mixture with the consequense of an too high temperature through which the mixture will explode before the spark. Or you're carb-jet is too small, or you should check voor 'false air'?
 
CIH racing said:
heres what you do, and this is commen in AC yamaha/ minirelli engines. I worked on 100s of bores and easiest cheapest and safest fix is to do this.
Run 2 base gaskets, meaning, use the one that came in the kit, and keep the stock one on as well. This will give you enough clearence to prevent detonation. You wont have to run high octane gas or do an special tuning and lost power as a result. Just do that, and maybe i suggest putting your Carb needle on the richest setting to allow more fuel when you slack off after full throttle.
ALso if you dont do that, and you plann on running that bore for sometime ona stock crank, the upper rod will fail with in a few 100 miles from where. What brand of bike did you say its on?
Click to expand...

The cylinder was no longer of any use after detonation... piston was molten, etc. It had 2 base gaskets on it (thus the squish clearance of .762mm), engine held pressure just fine, etc. I just replaced it with an Athena cylinder kit and the fellow has been riding for about 2 weeks on the street and loves it. I never did get a chance to take it all home and look at it more. The Athena is holding up extremely well under the exact same conditions, so I'm not too worried about it anymore.
 

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