ESE's works engine tuner

[TZ350]

.
Like most people I guess, I just assumed that a 2S crankcases pressure behaved like a 4S inlet manifold. Low pressure when the throttle was closed and high when the throttle is open. But for a 2S that is not true, in fact its the complete reverse and another example of the mistake of trying to apply 4S thinking to a 2S.

[lodgernz]

Anyone tried Pyro Putty 1000 before?
http://www.aremco.com/ceramic-metallic-pastes/
Just bought some, approx $100AUD for a kit which makes about 250ml. Going to try it in the exhaust duct and AUX EX ports to test different shapes before welding/replating. Fingers crossed it holds together long enough to get some decent dyno runs in.

I used it to lower the Aux ports on a Rotax 257 for sprint kart use.
Worked fine.
But the issue with filling the main duct with it means the ceramic putty will be a first class insulator - the retained charge will overheat
and you will loose power.
No matter how good the " shape " may be.

Wobbly, do you think this would be OK for transfers? I'm finding DevCon a bit unreliable.

[F5 Dave]

Was that the issue on Sunday?
Cleanliness is next to Godliness (trying to work a suitable joke in there, work in progress).
Also centre punch marks to give something to key onto.

Presumably some engines with less blowdown will fire hotter and longer ex gasses down the transfers.

[lodgernz]

Was that the issue on Sunday?
Cleanliness is next to Godliness (trying to work a suitable joke in there, work in progress).
Also centre punch marks to give something to key onto.

Presumably some engines with less blowdown will fire hotter and longer ex gasses down the transfers.

No. The issue on Sunday was 6-month-old fuel. Both normally reliable engines detoed their pistons to death.
Very embarrassed.

The issue I'm having with DevCon is getting it to cure. No matter how accurately I measure the quantities, and provide appropriate recommended curing temperatures, it remains sticky and able to be dug out.
Maybe past its best by date, but everything I've read says there's no shelf life limit.

[F5 Dave]

There was a chap doing 4 stroke inlets with JB Weld. I've got a few tubes if you want to try it. Seems fine. Can get singles at Mitre10.

[diesel pig]

Maybe past its best by date, but everything I've read says there's no shelf life limit.

I was on the Devcon site the other night and I am pretty sure it said Devcon F had no shelf life limit if unopened but once opened it would last about 3 years.
How long has it been since you opened your lot?

[husaberg]

According to the figures JB welds adhesive strength is lower.
http://iedaddy.com/2011/09/many-uses...con-is-better/

if the devcon is going off properly thats more likely the issue imo.

highest temp stuff i have seen
https://www.aremco.com/ceramic-metallic-pastes/

[lodgernz]

I was on the Devcon site the other night and I am pretty sure it said Devcon F had no shelf life limit if unopened but once opened it would last about 3 years.
How long has it been since you opened your lot?

Probably about 3 years. Bugger.

[Flettner]

.
Like most people I guess, I just assumed that a 2S crankcases pressure behaved like a 4S inlet manifold. Low pressure when the throttle was closed and high when the throttle is open. But for a 2S that is not true, in fact its the complete reverse and another example of the mistake of trying to apply 4S thinking to a 2S.

A discovery of significance and no one seems to notice😎
Keep up the good work, I'm watching.

[jonny quest]

Awesome stuff TZ350. I had about 5 things to rationalize, then I remembered you're rotary valve... would it be similar in case reed scenario? I started thinking too much and I hypothesized too many things that made sense then didn't make sense, lol. Great work. I'm going to have to re read your posts multiple times

[TZ350]

Awesome stuff TZ350. I had about 5 things to rationalize, then I remembered you're rotary valve... would it be similar in case reed scenario?

I have not checked but I expect so, rotary valve, 24/7, reed, case reed or piston port would all have the same crankcase pressure scenarios. If anyone wanted to, they could use something like EngMod2T to check.

The lowest crankcase pressure is with the piston at TDC, and that makes sense.
The highest crankcase pressure is with the piston about 140 ATDC, sort of makes sense too.

At 140 ATDC the inlet is closed and the transfers and exhaust port are open. Some mixture is flowing out the transfers but not fast enough for all of it to escape before the piston gives the remaining mixture in the crankcase a hurry up.

The pipe should be starting to suck real hard around that point too, so you have a real push pull situation accelerating the transfer of fresh charge into the cylinder.

If the pipe is not sucking that hard you will have a higher residual pressure left in the crankcase. That explains why at idle and low throttle at low revs the crankcase pressure is higher than when the throttle is wide open and the motor is singing on the pipe. With high crankcase pressure exhaust gas pollution explains why when the throttle is closed the motor slows down to an idle.

At idle the motor is running on a very small amount of fresh air mixed with a lot of pollution that has back flowed from the exhaust. I am not sure if the crankcase is full of pollution or its full of clean mixture and only a small amount is being transferred to a cylinder full of un scavenged pollution, maybe a bit of both so the story is not completely told yet.

But one thing is for sure, the crankcase pressure is higher at idle and low throttle than it is at wide open throttle with the motor making real power.

[breezy]

I have not checked but I expect so, rotary valve, 24/7, reed, case reed or piston port would all have the same crankcase pressure scenarios. If anyone wanted to, they could use something like EngMod2T to check.

The lowest crankcase pressure is with the piston at TDC, and that makes sense.
The highest crankcase pressure is with the piston about 140 ATDC, sort of makes sense too.

At 140 ATDC the inlet is closed and the transfers and exhaust port are open. Some mixture is flowing out the transfers but not fast enough for all of it to escape before the piston gives the remaining mixture in the crankcase a hurry up.

The pipe should be starting to suck real hard around that point too, so you have a real push pull situation accelerating the transfer of fresh charge into the cylinder.

If the pipe is not sucking that hard you will have a higher residual pressure left in the crankcase. That explains why at idle and low throttle at low revs the crankcase pressure is higher than when the throttle is wide open and the motor is singing on the pipe. With high crankcase pressure exhaust gas pollution explains why when the throttle is closed the motor slows down to an idle.

At idle the motor is running on a very small amount of fresh air mixed with a lot of pollution that has back flowed from the exhaust. I am not sure if the crankcase is full of pollution or its full of clean mixture and only a small amount is being transferred to a cylinder full of un scavenged pollution, maybe a bit of both so the story is not completely told yet.

But one thing is for sure, the crankcase pressure is higher at idle and low throttle than it is at wide open throttle with the motor making real power.

TZ, I Think you already new this, but being told and seeing it for yourself is two different things. Seeing this information for me helps to realise the the significance of blow down , flow reversal ,lower and wide transfer ports, poor idling at low rpm, exhaust function taking over from engine pumping as rpm increases.

[dutchpower]

But one thing is for sure, the crankcase pressure is higher at idle and low throttle than it is at wide open throttle with the motor making real power.

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[dutchpower]

But one thing is for sure, the crankcase pressure is higher at idle and low throttle than it is at wide open throttle with the motor making real power.

[/QUOTE]

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[jonny quest]

So, when a 2stroke comes "on pipe" is it the crankcase having a clean mixture versus a polluted mixture in crankcase?