Author Topic: running hot after rebuild  (Read 730 times)

Offline Guy Wilson

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running hot after rebuild
« on: 22.09. 2018 16:18 »
I've just started my 1955 Gold flash after a long period of inactivity and an engine rebuild.. Its runs ok but not fine.
Its running very hot and the oil tank is hot to touch after about 30 minutes of running around.
I'm suspecting the ignition is retarded. The engine doesn't instantly drop off when the throttle closed. (the cable is free and not trapped)
Ot was running on 250 main jet (I'm at 6000ft above sea level) its now on a 210 main jet - maybe too lean?
Any suggestions? I'm hoping to ride the DGR next weekend and only have a few days to solve this...
Many thanks
Guy

Offline RichardL

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Re: running hot after rebuild
« Reply #1 on: 22.09. 2018 16:43 »
Too lean and too much advance, I think.

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Offline RDfella

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Re: running hot after rebuild
« Reply #2 on: 22.09. 2018 16:45 »
How much running in has it done? After rebuilding my '58 GF, I could not hold the oil tank after ten miles. After 50 miles or so that reduced considerably. You've got to expect lots more friction (heat) until it's run in, especially if the rebuild included rebore etc. Obviously if it's running lean it'll get hot. Try a plug chop to check. Does it hesitate or seem sluggish at any particular throttle opening? Remember main jet only affects 3/4 to full throttle. Below that it's slide cutaway (1/4 to 1/2)and and then needle (1/2 to 3/4). Approximately.
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Offline RDfella

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Re: running hot after rebuild
« Reply #3 on: 22.09. 2018 16:49 »
Guy - forgot to address the ignition issue you raised - yes, retarded would make it run hot. Over advanced no, that would cause it to kick back on the kickstart and possibly ping (pink, depending on country) under load.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Offline RichardL

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Re: running hot after rebuild
« Reply #4 on: 22.09. 2018 16:52 »
Oops. Thanks for correction RD.
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Offline Guy Wilson

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running hot after rebuild
« Reply #5 on: 22.09. 2018 17:03 »
thank you.
Its not run in yet at all  - maybe 10 miles at most.
reassuring about the oil oil tank heat.
I'll go back to the 250 jet tomorrow and check the ignition timing.. whats the correct timing before TBC?
Guy

Offline RDfella

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Re: running hot after rebuild
« Reply #6 on: 22.09. 2018 18:29 »
The GF should be 11/32 inch before TDC. Remember to jam the auto advance at full advance when you do this, otherwise you'll be way over-advanced.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Offline coater87

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Re: running hot after rebuild
« Reply #7 on: 22.09. 2018 22:06 »
The GF should be 11/32 inch before TDC. Remember to jam the auto advance at full advance when you do this, otherwise you'll be way over-advanced.

 I thought we were shooting for 5/16 with an iron head and 7 something compression?
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Online morris

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Re: running hot after rebuild
« Reply #8 on: 22.09. 2018 22:08 »
"Hot to the touch" is not really scientific...  *smile*
After a good hard ride the oil tank can reach over 50° which feels really hot to the touch. After all, you would boil an egg at 60°C
The temperature of the head after a ride measured near the spark plugs can reach 120°C
Try get hold of a temperature gun or probe. That'll tell you more
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Online Greybeard

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Re: running hot after rebuild
« Reply #9 on: 22.09. 2018 22:48 »
The exhaust headers blued up when I put my bike back on the road six years ago.

Offline Guy Wilson

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running hot after rebuild
« Reply #10 on: 23.09. 2018 05:13 »
What I hadn't done was to jam open the advanced / retard unit..The timing is probably way out as a result..

Offline RDfella

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Re: running hot after rebuild
« Reply #11 on: 23.09. 2018 13:41 »
coater - think you'll find that's for a std A7. According to my Haynes manual, the A7 is 5/16, the A7SS is 3/8, the A10GF is 11/32 and the A10SF / RR / SR is 3/8
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Online Black Sheep

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Re: running hot after rebuild
« Reply #12 on: 23.09. 2018 14:06 »
Certainly with UK petrol now having a lower octane rating than before, 5/16" btdc would be more appropriate. Generally, retarding the ignition timing a couple of degrees these days is seen as no bad thing. This may not apply elsewhere.
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Online JulianS

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Re: running hot after rebuild
« Reply #13 on: 23.09. 2018 14:42 »
The figure 11/32 (34 degress BTDC) was first given by BSA in 1950 and at that time the only petrol availabe in the UK was dreadful 80 octane pool petrol. Much worse than that which is available here today.

Interesting snippet from Hansard November 1950 following a question in the House of Commons;

https://api.parliament.uk/historic-hansard/commons/1950/nov/13/pool-petrol-standard

Another interesting article from 1953 Motor Sport magazine on the reintroduction of branded petrol o UK market that year.

https://www.motorsportmagazine.com/archive/article/february-1953/22/enthusiasts-directory-no-5-branded-petrol

Offline Guy Wilson

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running hot after rebuild
« Reply #14 on: 23.09. 2018 16:23 »
Retimed to 11/32 roughly and it runs a lot better. more power / clutch is slipping now. It still running super hot though when I stop. The oil tank is still hot / too hot to touch with a bare hand..
I'll change the oil. I have straight 40 in it at the moment...