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Author Topic: Supercharged Hillman Imp engined bike  (Read 19652 times)
Dslam
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Wot ho chaps, its bloody Whitworth!!


« Reply #30 on: July 10, 2012, 10:05:41 PM »

Thanks Mr Bandit and Mr Manky.
I really don't see myself a particularly skilled engineer but live by the addage that if it looks right it probably is and if at first you don't succeed you ammer aint big enough Grin Grin Grin
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fifer
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« Reply #31 on: July 10, 2012, 10:19:35 PM »

Stunning  Smiley
Brings back lots of memories of the sixties / early seventies .
I had a 3 wheeler Bond 875 which was fitted with the Imp engine in the early seventies and , with the engine in the rear ,  the front end got very light at speed  Grin.
.
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« Last Edit: July 13, 2012, 09:59:11 PM by fifer » Logged

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Cabman77
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« Reply #32 on: July 11, 2012, 07:44:01 PM »

That crank looks like a very well toughened article, nice to see such attention to detail. Lovely looking thing I must say.
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Dslam
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Wot ho chaps, its bloody Whitworth!!


« Reply #33 on: July 13, 2012, 06:50:21 PM »

Thanks Cabby,
Its nice to have my work appreciated. Everyone at the festival seemed pleased to see another historic drag/sprint bike resurrected.
Youtube link to see and hear it running;

http://www.youtube.com/watch?v=ZdOv_DBkvlY
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Manky Monkey
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« Reply #34 on: July 13, 2012, 07:09:09 PM »

Cool!
That's Mr Dslam in the blue sweatshirt by the way.
I've always wondered why race bikes have to be constantly revved like that. I can understand them being highly tuned & not having a steady tick-over, but wouldn't a constant rev be better for the engine? 
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Dslam
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Wot ho chaps, its bloody Whitworth!!


« Reply #35 on: July 13, 2012, 08:36:09 PM »

Because the supercharger is dumping so much mixture into the chambers at low revs you need to rev it regularly to clear the unburned fuel. You can see in the video it looks really rich but at full chat its clean. The smoke goes slightly blue as the blower has an oil feed which ends up being burned. Bearing in mind the engine is tuned for flat out power only. The blower is running at 25lbs of boost at max revs which leaves it at about 10 at high tickover revs. The motor cannot cope with that much fuel at such low revs and we run the risk of severe bore wash (the fuel washes the oil off of the bores and the rings wear very fast indeed) or worse, the blower gets droplets of fuel laying in it. BOOM!!
What is interesting is that after less than a minute of running the blower is encased in ice where the fuel is vaporised and acts as a refridgerant on the body. The slow run back to the paddock gives it time to thaw out. I remember some years ago riding Ron Mays' (Sadly no longer with us) blown Triumph which the blower used to be fully encased in a 6mm block of ice after each run. A bit worrysome at first but the carb had an unsulator block between it and the inlet manifold so it would only ice the carb if you ran it in temps below 10 degrees. That was scarry!
 We were attempting to get some rapid heat into the motor as well to ensure we had measured the water jacket gasket correctly and that there were no leaks.
A constant tickover on race bikes is possible but on bikes such as these the cam is designed to open the inlet valves really fast to allow as much charge into the motor as possible and to take advantage of the pressure in the plenum chamber.
Imagine this, Take a breath and blow out through your mouth, easy and not remotely agressive. Now take a breath and blow your cheeks out (the ones on your face!!) whilst maintaining pressure open your mouth. You get a lungfull out in half the time. Also there is no overlap between the time the exhaust valve is closing and the inlet valve is opening. In a naturally aspirated engine this overlap helps scavenge the exhaust gasses out and the shock wave in the exhaust helps the fuel in. With a blower this simply blows fuel down the exhaust and wastes pressure.
So, having dealt with all that I think that tickover is unessesary Grin
« Last Edit: July 14, 2012, 05:11:08 PM by Dslam » Logged
Manky Monkey
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« Reply #36 on: July 13, 2012, 08:47:13 PM »

I think I understand!
Impressive mechanicking Andy.
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Dslam
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« Reply #37 on: July 13, 2012, 08:49:39 PM »

I just added a bit more Grin
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Manky Monkey
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« Reply #38 on: July 13, 2012, 09:44:11 PM »

O.K, now I've given up trying to understand.  Tongue
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spanners
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« Reply #39 on: July 13, 2012, 11:58:11 PM »

yep understood,,
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nabsim
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« Reply #40 on: July 14, 2012, 11:47:45 AM »

Gets a bit complex very quickly doesn't it? Smiley
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Dslam
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« Reply #41 on: July 14, 2012, 12:19:40 PM »

It gets really stupid when trying to work out airflow/air fuel ratio's/plenum chamber size/carb throat diameter. Does my head in as well but I have to go there soon as my new build is about to start.
An old school blown pre unit triumph drag bike. I am scratch building the frame as well. I think I might start a new thread for that one.
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Dslam
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« Reply #42 on: July 14, 2012, 01:07:24 PM »

Next episode;....................

Arrived at Mallory on Friday amidst tropical rainfall. The fear was the whole weekend would be cancelled. The paddock was awash with rivulets running everywhere.
Set up camp and got the bikes out. The Imp, My Triumph Sprinter and my Triumph road bike which is a total bitsa (most of my stuff is). A 1951 tiger 100 rigid with a generater engine.
By 6pm the rain had stopped and the track begun to dry. Off to the beer tent then. The rest of the evening was a bit vague Grin
Saturday dawned. Big breakfast in the paddock cafe (best brekkie ever) and off on scrutineering duties.
Ran the road bike in two sessions on Saturday. That was fun. Don't often get the chance to give it the beans on the road.
Lets move on to Sunday as Saturday night is a bit of a blurr. All I remember is laughing so much it hurt.
Paul, the owner, had told me that Mickie pierce and Vic Phillips, contrary to popular belief, are both alive and kicking, in their mid 70's and living in the south east. Near me. Paul had invited both and got passes to them. Unfortunatly for us, Vic had to go to Thailand with his new bride!!!! but Mickie was really keen to attend. He duly arrived and after introductions were made we checked out the bike. I could see in his face that he had been transported back 40 years. A sight that will stay with me for a very long time.
Mickie came up to me, put his arm over my shoulder and wispered "you done a bloody good job of that boy"!
Compliment indeed. It made the last 7 months so worth while. Paul was on top of the world getting his bike back in tip top shape and having the approval of Mickie was the cherry on the cake.
We ran the bike up in the pit garages as you can see in the earlier link and everones faces lit up. She is loud and revs like a modern jap 4. A whiff of throttle and the revs have peaked. Brilliant.
Paul had the honour of first dibbs (it is his after all) and we took it onto the straight and fired her up. I could see in Pauls face that he was going to give it the biggun even though I has said please take it easy as it hasn't moved under it's own steam for 20 years. I was concerned also as the oil pressure was dropping. You can see me and Paul in the video looking at the oil pressure guage on the lh side. We suspect the bypass valve or the guage but you have to believe what the guage is telling you until you prove otherwise.
Paul got on board and asked me to engage gear as his foot is a bit knackered after too many years grasstracking and speedway riding. I made the snap decision to put the bike in second but unbenown to me he had pushed into second so I had put it into 3rd.
The flag dropped and Paul pulled away. Even though it was in third it started to pick up speed and by the 100 foot the revs were climbing fast. It is not usual to do a shakedown run in front of 20 000 people but hey.
As paul came back into the paddock I got onto my Sprinter and did a couple of runs. I wasn't aware tht he had had a couple of dramas. Apart from the 3rd gear thing he had his left foot near the exhaust outlet which promptly burned through the toe and burned his foot. He said he was really pi**edat this because it wasn't his sock changing month and that it was the only decent foot he has left! Also, there is a plug which blocks an oil take off at the back of the block which we will use to pressure feed the blower in due course. Said plug blew out, I know not why, and covered paul with oil down his right side.
A burned foot and oil soaked leather the test was declared a success. Grin
We rolled the bike into the display tent for the rest of the afternoon where we decided on the plan of action for it's next shakedown meeting. A full quarter at Wroughton.
Watch this space!!!
The photo's are Me and Paul on the main straight at Mallory. I am the one with no hair, and Mickie on Impulse time travelling some 40 years.
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Manky Monkey
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« Reply #43 on: July 14, 2012, 10:17:17 PM »

Fabulous!  Grin

"The paddock was awash with rivulets running everywhere".

-those rivulets are buggers aren't they. Should've left 'em at home with a rivulet sitter.
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On the last freedom moped out of Nowhere City.
Dslam
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Wot ho chaps, its bloody Whitworth!!


« Reply #44 on: July 15, 2012, 06:34:38 AM »

I knew I should have taken my rivulet gun Grin
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