RM250B deleted reed valve

[noisy toy]

So i have put the RM engine in the PE frame, found a couple of things. The 250 engine came out of a very bodgy 125c conversion .  An RM 1250?      The carby that was on the engine was 32mm, maybe from the 125 engine? I have put the 36mm from the PE engine on it. OK now to start. Nothing. Check spark. Nothing! Bugger, maybe thats why they stopped riding the dangerous POS 1250 before i got it. I think i will change to the PE CDI unit, or i may have to put the PE flywheel and coils on it, as the RM  harness plug is different to the PE plug, so i may as well change the whole lot. Is there much difference in the curves ets between the PE and RM? I have an RM 370 CDI unit too , worth a try? Lots of questions, sorry....
Cheers, Shane

[Lozza]

well i will stick with what ive been taught at tafe and at yamaha schools they are still teaching it right now put up some links or post some info before i will change my mind

I'm not out to change your mind you can believe whatever you want to believe. If you believe a basic Tafe course will teach the detail that  A Graham Bell does( who inspired and contines to inspire a generation of two stroke tuners around the world) then keep beieving that.His book Two Stroke Performance Tuning continues to be my first point of refernce for any two stroke related matter. Plenty of free downloads on the net or Graham still sells them via his Maitland based website.
Pg 49


 

[head]

well i will stick with what ive been taught at tafe and at yamaha schools they are still teaching it right now put up some links or post some info before i will change my mind

I'm not out to change your mind you can believe whatever you want to believe. If you believe a basic Tafe course will teach the detail that  A Graham Bell does( who inspired and contines to inspire a generation of two stroke tuners around the world) then keep beieving that.His book Two Stroke Performance Tuning continues to be my first point of refernce for any two stroke related matter. Plenty of free downloads on the net or Graham still sells them via his Maitland based website.
Pg 49


 

You are taking that out of context. All he is saying is that they have gone away from high crankcase pressures in building engines. It still needs crankcase compression to move the air/fuel mixture through the transfers. No longer are they seeking a high pressure though. The modern two stroke still has the free spaces in crankcases and crank  removed or stuffed. Stuffing the crankcases and crank can still work on early two strokes and does give a good power increase.

[crs-and-rms]

so the decending piston still compresses the air fuel mixture in the crankcase and moves the air fuel mixture throught the transfer ports which is all i said in my first post and id rather have a tafe certificate than just a graham bell book

[LWC82PE]

The key word there for me is 'HIGH' crankcase compression.

[Lozza]

Must be the month for old wives tales to do the rounds again
Sure your not taking the text 'out of context' ?It states they have 'got away from the IDEA' nor does it say case compression is  required for transfer flow to occur. If high case compression doesn't push fuel through the transfer how will low case compression ever  do that? The decending piston increases case compression by a factor of 0.1ie you have 1.3 case comp the decending piston moves it to 1.4, however above the ring we have far greater residual combustion pressure long after the transfer ports have opened. How is it possible for air/fuel that is at best under 5psi pressure overcome pressure that is still well over 100psi? It cannot without the aid of the pipe,as it's not untill BDC does mass bulk flow from the transfers occur( which again proves the decending piston pushing anything at anytime as crock of shit).Bulk flow in the transfers occurs at BDC because the lowest pressure in the engine is in the header pipe, the highest in the inlet tract.
Stuffing cases really only brings the power lower down the rev range it cannot increase output of an engine, the effect is similar to high secondary compression(that increases the output).Works lower down the rpm range as rpm rises the engine struggles to overcome the pumping losses.

Here's a snapshot from a basic widely used and trusted simulator. Shows the transfer duct 1 with the port 1/4 of the way open and air/fuel velocity in that duct to be -100 ft/s


then we have velocity in the same duct at BDC

[DR]

no need for any disputes guys

Whilst I do sometimes refer to reference books and take others opinions aboard there is only 1 'real and for sure' way to know the answer.... TRY IT!

You can speculate all you want with facts and figures but a few minutes on the bike will answer every question. Easiest way is to simply take it out and ride it

[noisy toy]

Hey Lozza, that simulator looks like an interesting tool, where can i get hold of one? I am still having spark issues with the old girl, but i do intend to ride it with and without the reed, just for the hell of it. I am not sure if the results will be the same as before, as it had a 32 mm carb on before and i have fitted the 36. I may as well try both there too. A dyno would be good so i could post up some curves, i see what i can do.
I am surprised no one else has responded that has actually tried this?
I will try to take some decent pics of the porting when i have the barrel off next.

[noisy toy]

I got the old PE running properly , finally. I swapped coils and rotors and still no success with the         no-spark issue. So i thought bugger it, i will remove the RM engine, swap the barrel and piston to the PE bottom end and chuck it back in. Bingo! A gentle test ride, but still enough to fill my jocks. It goes quite well! It even idles and everything.I gave it a bit in the drive way, it took me by surprise and stepped out sideways a bit then took off toward the shed! It was about now i remembered the front brake was not connected yet,(it is now)and the rear,well,... I may as well have held my hat out for a similar effect.But i missed everything and made it back in to the shed to fix the last few things.Will report after the first proper ride.
Cheers. 

[lukeb1961]

It was about now i remembered the front brake was not connected yet,(it is now)and the rear,well,...

We have had some ugly moments on the PE list where people have taken a PE around for a quick blast sans brakes. Good to hear you have now fitted the front brake!
Luke

[pancho]

 While skimming through this post I saw the comment re stuff learned at T.a.f.e etc,
 While not wishing to denigrate tech trade courses I came to realise  that a lot of what I was taught at tech in the auto mechanic course was 'simplified'.
 Natural trade curiosity on my behalf drew me to the conclusion that the primary aim was to educate students to a point where they had enough info to provide confidence in making accurate diagnoses of  faults.
 While saying this I am also convinced that some teachers didn't understand what was going on.
 A classic example was the bulls*** explanation of the Kettering ignition system [common on everything prior to true electronics]. e.g. "the condensor is nothing but an electrical shock absorber to stop arcing at the points", and also some of the truly weired explanations of cam design.
 My conclusion is not to take for granted that which you learned yesterday is gospel, research more if you wish to learn. cheers pancho.
 

[pancho]

 I should have added that my knowledge of two stroke engines is very limited having being taught at tech in the days when 2/'s were strictly for small low performance industrial engines and considered by lots to be useless for anything else.
 Thats why I find these discussions so informative cheers pancho.

[Lozza]

Hey Lozza, that simulator looks like an interesting tool, where can i get hold of one?

HERE