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BSA Thunderbolt 1970 basic questions
#809113 05/16/20 3:44 pm
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Hi
I have worked on bikes all my life manly Jap bikes. So I think I can say I am experienced. However never worked on a Brit bike and currently have a thunderbolt on my lift.

Please can someone answer three simple question.

1 What is the correct gap for inlet and exhaust valves.

2 what is the correct static timing. I have a lucus unit in it. I will try to attach pictures.

3 What oil should go in engine, type and grade?

If any one lives near Newark Notts and knows these bikes please feel free to help.

Thanks

Dennis

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Re: BSA Thunderbolt 1970 basic questions
dennisthemenace #809123 05/16/20 6:28 pm
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Hi Dennis.

The inlet should have 0.008” gap
The exhaust 0.010” gap

If you remove the 3” disc on the primary side there is a pin which will line up with the timing marks on the rotor, this mark is at 34° (providing the pin is in the left hand hole) the points cam should be under tension as this is the fully advanced timing mark. Depending how strong the advance springs are, the full advance will be between 2000 and 3500 rpm. The closer to that 3500rpm mark the more torquey the engine will feel. If you have a strobe light you’ll need this to ensure both sides are timed the same.

As you don’t know what is in at the moment, a good 20-50 mineral oil will be fine. Morris V-Twin is a very good oil.

Unlike the Jap bikes the gearbox and primary drive use separate oils. The primary will be fine with SAE 20 mineral oil. Some recommend ATF

For the gearbox EP90.

Last edited by Allan G; 05/17/20 2:58 pm.

Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Re: BSA Thunderbolt 1970 basic questions
Allan G #809142 05/16/20 10:24 pm
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Originally Posted by Allan G
If you remove the 3” disc on the primary side there is a pin which will line up with the timing marks on the rotor, this mark is at 34° (providing the pin is in the right hand hole)

Allan,

I believe you meant the left hand hole.


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project
1971 BSA A65 650 - Project
1972 Norton Commando 750 "Combat"


"Every time I listen to AC/DC, so do my neighbors"

Re: BSA Thunderbolt 1970 basic questions
Allan G #809166 05/17/20 9:24 am
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Hi Allan

Thank you very much for taking time to help me. I have ordered a Haynes manual which has not arrived yet. Normally I can find sufficient information on the Web or even get a pdf version but not in this case.

I will set valve gaps accordingly.

I had already removed the dusk on primary drive cover and saw no pin but will check. I now have the complete primary drive cover off.

How do atrach pictures to this thread,,?

Very interesting about 3 different oils. The engine oil obviously goes in tank and has a dip stick, is the level measured hot or cold?

Where are the fill and level points for gearbox and primarily drive. Obvoisly I can see several points oil could be added but what level?

If I understand you correctly the mark on rotor is 34 btdc. It should line up at 3500 rpm? How do I set static timing for ball park?

Thanks for your help

Dennis

Re: BSA Thunderbolt 1970 basic questions
dennisthemenace #809168 05/17/20 10:23 am
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The timing pin should be in the LH hole. This clearly shown fig B86 on page B49 of the 1970 manual.and in figure B85 on page B53 of the 1971 manual. The Rh position was for Energy transfer models.

Doesnt matter at this stage,
The haynes manual is better than nothing, especially if you need to cover different years.
Try to get a year specific factory manual, available on E bay, this will be much more detailed.

Attaching pictures is a test, if you cant figure it out, you shouldnt be working on the engine.
Take pic on digital camera, upload to a host site like Imageshack ( dont use photobucket) , from the host site you get a URL that can be used to post a pic in the thread. Its very clunky.Images must be below a certain file size, dont go Giga pixel.
Or pay Morgan the ransom/ membership fee and you can skip the host site part. This is why Farcebook BSA pages are thriving.The trouble with FB is stuff moves fast and there is a huge amount of duff gen, this site is a bit more fixed and bad info is less common, it still pays dividends to RTFM.
There should be a manual timing plug in the front lower RHS of the crankcase, remove the plug, turn engine until a detent slot in the flywheel allow a 3/16 diam rod to engage, there is a factory tool, but an allen key shank will be close enough, the slot is at the full timing advance position so the advance retard mech needs to be wound round against its spring tension.

Last edited by gavin eisler; 05/17/20 10:41 am.

71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: BSA Thunderbolt 1970 basic questions
dennisthemenace #809170 05/17/20 10:58 am
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Oils and levels.
Engine, check after running, so the sump is clear, after a few days / weeks oil dribbles into the crank case, know as wet sumping, if you top up the tank before a run and it has wet sumped the tank will overfill as the sump clears and make a huge mess.
Use 20 50 bike oil.

Gearbox, the cream plastic cap should have a dipstick on it, use that, fill with EP 90 gear oil. Change annually

primary chaincase, near the footrest are two small screws that are not on the case perimeter, upper is level, lower is drain.
I like Auto Transmission Fluid ( ATF) , others use a light oil around 20 w, oil must not contain friction modifiers or the clutch will slip. Change when doing the engine oil. If you use a thick oil in here the chain will wear fast as it cuts a groove through heavy oil with little penetration.

The factory suggests oil changes at 4,000 miles, this is too long, most folk change between 1000 - 2 000 miles.
Oil is cheaper than engine parts.


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: BSA Thunderbolt 1970 basic questions
dennisthemenace #809177 05/17/20 12:23 pm
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These bikes do not have oil filters This is why oil should be changed as often as Gavin says.

Re: BSA Thunderbolt 1970 basic questions
dennisthemenace #809178 05/17/20 12:35 pm
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Hi Allan

Thank you very much for taking time to help me. I have ordered a Haynes manual which has not arrived yet. Normally I can find sufficient information on the Web or even get a pdf version but not in this case.

I will set valve gaps accordingly.

I had already removed the dusk on primary drive cover and saw no pin but will check. I now have the complete primary drive cover off.

How do atrach pictures to this thread,,?

Very interesting about 3 different oils. The engine oil obviously goes in tank and has a dip stick, is the level measured hot or cold?

Where are the fill and level points for gearbox and primarily drive. Obvoisly I can see several points oil could be added but what level?

If I understand you correctly the mark on rotor is 34 btdc. It should line up at 3500 rpm? How do I set static timing for ball park?

Thanks for your help

Dennis

Re: BSA Thunderbolt 1970 basic questions
dennisthemenace #809190 05/17/20 1:32 pm
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Dennis, are you in an echo chamber?


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: BSA Thunderbolt 1970 basic questions
Jon W. Whitley #809205 05/17/20 2:55 pm
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Originally Posted by Jon W. Whitley
Originally Posted by Allan G
If you remove the 3” disc on the primary side there is a pin which will line up with the timing marks on the rotor, this mark is at 34° (providing the pin is in the right hand hole)

Allan,

I believe you meant the left hand hole.

Correct and thanks, a Doh moment. Will edit the original post


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)


Moderated by  Allan G, Jon W. Whitley 

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