The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Guy Wilson on 22.09. 2018 16:18

Title: running hot after rebuild
Post by: Guy Wilson 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
Title: Re: running hot after rebuild
Post by: RichardL on 22.09. 2018 16:43
Too lean and too much advance, I think.

Richard L.
Title: Re: running hot after rebuild
Post by: RDfella 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.
Title: Re: running hot after rebuild
Post by: RDfella 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.
Title: Re: running hot after rebuild
Post by: RichardL on 22.09. 2018 16:52
Oops. Thanks for correction RD.
Title: running hot after rebuild
Post by: Guy Wilson 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
Title: Re: running hot after rebuild
Post by: RDfella 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.
Title: Re: running hot after rebuild
Post by: coater87 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?
Title: Re: running hot after rebuild
Post by: morris 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
Title: Re: running hot after rebuild
Post by: Greybeard on 22.09. 2018 22:48
The exhaust headers blued up when I put my bike back on the road six years ago.
Title: running hot after rebuild
Post by: Guy Wilson 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..
Title: Re: running hot after rebuild
Post by: RDfella 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
Title: Re: running hot after rebuild
Post by: Black Sheep 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.
Title: Re: running hot after rebuild
Post by: JulianS 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
Title: running hot after rebuild
Post by: Guy Wilson 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...
Title: Re: running hot after rebuild
Post by: Guy Wilson on 23.09. 2018 16:33
11/32 is .34 of an inch or 8.7 mm? I think I've now set the mag timing for half that...
So at TDC on the compression stroke I'd back the piston back down the barrel 8.7mm and set the mag timing (while fully advanced) to open the points at this mark...sorry if that sounds obvious, I'm trying too get it 100% straight in my head...
Title: running hot after rebuild
Post by: Guy Wilson on 24.09. 2018 07:12
I think I've set up TDC on the left hand cylinder and then time the mag to the right hand cylinder.... that might explain a few things...
Guy
Title: Re: running hot after rebuild
Post by: Greybeard on 24.09. 2018 09:08
11/32 is .34 of an inch or 8.7 mm? I think I've now set the mag timing for half that...
So at TDC on the compression stroke I'd back the piston back down the barrel 8.7mm and set the mag timing (while fully advanced) to open the points at this mark...sorry if that sounds obvious, I'm trying too get it 100% straight in my head...

It's best to back off then go forward to the firing position so backlash in the gears is taken up.
Title: Re: running hot after rebuild
Post by: Greybeard on 24.09. 2018 09:14
I think I've set up TDC on the left hand cylinder and then time the mag to the right hand cylinder.... that might explain a few things...
Guy

Nah, that won't be a problem; remember both pistons are at the firing position at the same time; just valves are doing their own thing.
Title: Re: running hot after rebuild
Post by: Rex on 24.09. 2018 09:45
If you've only done ten miles or so on a newly-rebuilt engine then you're unlikely to have gone into the "main jet zone" for any length of time, if at all, so I'd concentrate on timing issues if I were you..
Title: running hot after rebuild
Post by: Guy Wilson on 24.09. 2018 16:31
Thank you again gents..I retimed the magneto today - correctly this time I believe - I had it advanced by 50% or 4mm.
Planning on a longer run tomorrow to see how it holds together..
The only reason its running at all is because of this forum and I appreciate all the time and attention given freely from around the world..
Guy
Title: running hot after rebuild
Post by: Guy Wilson on 25.09. 2018 12:15
I managed 55 miles this morning with no real problem and as RDfella rightly predicated, its running al lot cooler now..thank you all gents!
I'll post some photos of the DGR run next week hopefully with the bike running and not me repairing it by the side of the road..although that's also part of joy of old bikes...
Guy
Title: Re: running hot after rebuild
Post by: RichardL on 25.09. 2018 12:53
Guy,

A few of us keep trying to expand forum interest in the DGR. We have formed a forum team as part of this, but also for the camaraderie. Unless you're using a pseudonym (though, I think I know all of them) I don't see you there. Please consider joining the team. Your individual fundraising remains in your name and is also added to the team total (no cost tou you, of course). Here is the link:

https://www.gentlemansride.com/team/bsaaa0forum

Richard L.
Title: Re: running hot after rebuild
Post by: Guy Wilson on 25.09. 2018 12:59
I'm registered under the Kenya DGR team
https://www.gentlemansride.com/sponsor/country/kenya?ride_id=140
Title: Re: running hot after rebuild
Post by: Angus on 25.09. 2018 13:51
Hi Guy

I hate this DGR site.

I think that is the ride you are in, you can also be in a team which does not affect the ride you are in. I am on the Bury St Edmunds ride and in the forum team
Title: Re: running hot after rebuild
Post by: RichardL on 25.09. 2018 13:55
Angus beat me to it.

Richard L.


https://www.gentlemansride.com/fundraiser/bsaaa0forum