Classic M/C Mechanics piece on two stroke tuning. Nov issue

Number of posts : 166 Registration date : 2011-07-25

The November edition of Classic Motorcycle Mechanics has a multi page piece by Stan Stephens on two stroke tuning for classic engines. Basic, 'Boy Scout' advice with photos. Available to read in Tesco/WH Smith and all good retail 'reading libraries.'

Easily spotted as the cover has a photo of Steve Parrish's FZ750 with a number 6 racing plate. Starts on p84.

PS it could not be further from Trevor's technical discussion piece.

Subject: Maybe not further Jimmie.... Sat Oct 21, 2017 5:59 am

Maybe further from Trevor Jimmie,because the article might NOT be applicable to Piston Ported 2-stroke and meant for rotory or disc-valved or some other sort of valved 2 stroke engines ... I have no idea what was in Steve Parrish's FZ750 but have no doubt that it would not be a simple piston ported motor. I do know there was a 4-cylinder Japanese "Duck" that put terror into riders except Barry Sheene who upset the Japanese mechanics by hanging a 9 pound weight up front of the engine to stop it rearing its head at the slightest tweak of the throttle. The story went that only Barry was "Happy" to race it...The four intertwining exhaust pipes left only a toe-hold as place for attaching the feet ...
There is another factor here where a rider might prefer a high-toque engine to a high horsepower motor. I think it was so when Rossi got on the Ducati a few years back and discovered it was almost unrideable for him. I know that Terry Rymer preferred an engine with a humpy torque curve rather than having peak power coming in right near max engine speed. I was at a WSB meeting at Hockenheim when Fogarty slip-streamed Aaron Slight for the whole race up to the Motodrome bends. The low down speed torque allowed him to accelerate around Aaron with enough of a lead that Aaron could not catch Fogarty before the flag.

Cheers!

John.

john bass wrote:: I do know there was a 4-cylinder Japanese "Duck" that put terror into riders except Barry Sheene who upset the Japanese mechanics by hanging a 9 pound weight up front of the engine to stop it rearing its head at the slightest tweak of the throttle.

1n 1981/82 I got involved in sorting out a TZ350 engine with a "Camber" frame, made and designed by Alex MacFazean. As presented, this did indeed display the same tendancies. For my first try out/race we fitted about 8 or 9 pounds of lead (suitably labelled 16 Tons) to the front of the engine but very low down in the Vee of the fairing. It made it much more tolerable. Then later, looking at it on the bench, it dawned on me that the engine sprocket was quite a bit higher than the swing arm axis, so application of torque just compressed the mono shock. We made some new engine plates and rectified the issue completely.

"There is another factor here where a rider might prefer a high-toque engine to a high horsepower motor".

Yes, we had this when running Team No Limits in 1995. The 1994 rider Fernando Mendes used the RS250 like a 125, quite understandably as he was riding an RS125 in parallel, and had come from 125's.. For 1995 we were riderless from about March onwards and tried out a few riders like Woolsey Coulter and Lee Pullan (Wobblymans rider). We had gone from fast and reliable in 1994, to detonation in 1995. The motorcycle was the same but I spent a lot of time looking for possible causes, like air leaks, ignition timing etc. Then the data logging revealed they making good use of the lower speed torque and this gave us detonation. We would have had detonation in 1994 if Fernando had ridden in the same style!

Oh the wonders of hindsight

John.

Number of posts : 166 Registration date : 2011-07-25

Apologies for the confusion regarding my comment on the cover m/bike. This was to allow quick 'spotting' of the magazine for a quick (free) read in Tesco, etc.I get my online from the local library service and have today noticed that, in the shops, it is in a plastic bag, so a quick read in not possible. Ahhhhhhh!

Stan Stephens gives a quick run through the different types of two stroke engines - piston, reed valve, power valves - with a short introduction to the different aspects of tuning involved plus points to consider.

Subject: Hi Peter -- long time... Wed Nov 08, 2017 10:16 pm

Hi Peter, long time no hear...

How's retirement? -- farming instead Ford Dunton must be relaxing although I upset You-Know-Who by saying "Testing Operations," at Dunton, was really "Resting Operations"... .

Cheers!
John

Subject: Retirement? Thu Nov 09, 2017 4:51 am

Hi JB

Its now been 5 years since I ceased attendance at Dunton. Life here on the farm isn't all that relaxing. There is always something that needs fixing or mucking out.. I used to to go to work for a rest, now I cat nap where and when I can!

Cycle competition has been intense this season - I've won everything I set out to so no complaints there. Next year might be more difficult as we are taking 2 weeks in Vancouver, and I'll miss some championships rounds as a result. Its all a balancing act anyway.

Returning to engineering matters, I'm still waiting to see how many miles I can get out of my VW Golf's clutch and DMF. Its on 263,000 miles at mo, the clutch pedal bite point has been near the top for about the last 100,000 miles. Generally I think materials, machining processes, lubricants and fuels have come on so much since say the 1960's.

Dont see so much of the Boiler these days, but he still seems as keen as ever to make barrel castings for TZ's even.

All the best

Pete

Subject: Tuning what? Fri Nov 10, 2017 5:46 am

Hi Peter!
Biking from Cambridge to Essex to work at Dunton regularly was fantastic -- anyone'd need a rest ....???

Boiler sent me some info about WW2 aircraft and a report on US planes lost in Viet Nam. Awful lot of planes and lives lost for nothing but really intersesting aircraft.

Over-engineered -- by the sound of it -- that clutch. Much like KHD Canada Inc's v-8 for the HUMVVEE. Really daft part of my life that -- but I enjoyed nearly ten years of being in Canada and having money to spend on luxeries. We offered the American military an engine that would last for a hundred years with only only one major overhaul -- not really modern business was it?

Take care and warch where you are treading...

Cheers!

John-Boy

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