BTH COMPETITION MAGDYNO

General electrical problems
andrew zac
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BTH COMPETITION MAGDYNO

Postby andrew zac » Wed Apr 18, 2018 12:09 am

Hi . to all , i have a new BTH competition magdyno fitted to my VH . i used it at SELLBACKS BEACH in 2017 . the motor, and the rest of the bike ,wheels,bearings,rims,etc .was completely rebuilt and prepared for the event , pre race testing at a remote beach location on a measured race distance allowed me to select the correct gearing. i restricted my revs on the race week/end to 6000 . the magdyno is set at max 65000. however i know the motor will a taller gear and i am looking to increase my top speed from 80mph to a possible 95mph a gearing change and an increase in max revs should achieve this. my question is HOW do i reset the BTH to increase the max revs from 6500 to 7000 . i have contacted the supplier in the UK , he has never been asked the question and is not sure . see pics of my bike before and
IMG_2439.JPG
now in prep for 2019 regards Andrew
IMG_0041.JPG

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Eero.Korhonen
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Re: BTH COMPETITION MAGDYNO

Postby Eero.Korhonen » Wed Apr 18, 2018 6:56 am

Wow that is great! High piston, what is compression ratio? What is the size of that Concentric?
Br, Eero
Ariel VH 1954, IZH 350 1962, H-D Sportster Hugger 1992, AOMCC Member 133

Simon.Gardiner
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Re: BTH COMPETITION MAGDYNO

Postby Simon.Gardiner » Sun Apr 22, 2018 11:17 pm

Hi Andrew

Can't help with the problem myself but Tony Harris (who owned BTH until 7 years ago) looks into the forum occasionally, he might be able to help although as he hasn't jumped in on this so far maybe he can't....
(See eg in this thread for some of his 'history'
viewtopic.php?f=7&t=6376&p=42180&hilit=bth#p42180 )

Have you contacted the supplier - or the manufacturer ?

Mighty fine looking steed, by the way!

HTH in some small way.

SG
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)

andrew zac
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Re: BTH COMPETITION MAGDYNO

Postby andrew zac » Fri May 04, 2018 2:06 pm

ok Simon thanks for the reply . i am running H5 cam , 1.3/16 amal smooth bore , piston is a JP 9 to 1 hi comp . i am going to replace the gudgeon pin with a tapered one as it is a little lighter. i have other improvements in the pipeline as i begin to resemble thee complete bike in prep for the beach race events in feb 2019

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Brian_Walker
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Re: BTH COMPETITION MAGDYNO

Postby Brian_Walker » Fri Jun 01, 2018 4:33 am

Hi Andrew,
Bike looks real nice I was thinking of running a JP 9 piston in my VCH but I don't have an estimated weight for it, the picture below is my current one which weighs 485 gm and the pin 113gm. Would be interested what yours weighs as my old piston (the one with the hole was weighed when we still had ounces I don't remember, what it was which was shame as I balanced the crank for that piston, bit late now it has been lightened in an orthodox manner)
I did have a BTH mag and have copies of the service manual which seem to indicate the gear ratio is the limiting factor for rev range. I now have a Lucas SR1 and it ran fine at 7500 rpm, I don't what the specs are but maybe the lower speed limit for the BTH comp is based on testing where they look for a maximum number of "missfires by the magneto" on a test rig of 5%." these may not equate to engine missfires and at 100mph with a rigid frame you don't seem to notice much anyway.

Below is my two pistons, would also be interested how large the dome and valve cutaways were on the JP piston.
Cheers,
Brian

Keep us posted hows it runs on the beach.

Image[/URL]
1951-52 VCH under restoration


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