1958 Triumph pre unit 750cc alcohol - Yellow Bullet Forums
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Old 07-16-2019, 03:36 AM   #1
Drag lc
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Default 1958 Triumph pre unit 750cc alcohol

Hi,

I've been working on my dads old racing triumph pre unit 750cc the last few weeks I've put a new clutch basket and discs in it I've also fitted a new lithium battery aswell, I've given it a check over swell did the valve clearances .

now im not sure if any one here has had anything to do with these old engines, i seem to be struggling to find any info inline in regards to the timing with it being on alcohol. when dad raced it he never touched the timing so it was set at 28 deg it ran 90 mph at the strip with it like that I've since learnt its meant to be 38 up to 40 on petrol so I've bumped it around to 40 as the timing is locked and it has no kick starter so we have to push start it my thinking is if it was way to advanced it would not start nice or it would cough back when push starting it?.

with it at 40 it seems to start up nicer and it seems to sound not choked up like before .

i know from running a gm inline 6 down under on alcohol i added 5 deg straight up but this has a semi type combustion chamber so im looking if anyone has any advice on how much to add with it being on alcohol before we get it to the track? .

as we have currently added 12 deg and we know it went 90 mph before we should see a considerable improvement on mph straight up.

Cheers
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Old 07-16-2019, 07:59 AM   #2
Geoff
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Default Re: 1958 Triumph pre unit 750cc alcohol

Phil Irving's book Tuning for Speed lists the T120 as needing 41* timing. The T120 was the Bonneville, 650 cc. Comp Ratio or fuel type is not specified.
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Old 07-16-2019, 07:23 PM   #3
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Default Re: 1958 Triumph pre unit 750cc alcohol

you wouldn't believe it im reading tuning for speed right now I've not got to that part as im starting from the start. Cheers
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Old 07-17-2019, 07:18 AM   #4
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Default Re: 1958 Triumph pre unit 750cc alcohol

If it is a pre-unit construction, must have had a big bore kit fitted because 650 cc was the biggest Triumph at that time.
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Old 07-17-2019, 08:00 PM   #5
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Default Re: 1958 Triumph pre unit 750cc alcohol

Geoff,

yes mate that's correct i think it was a pretty comom mod back in the day.
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