Author Topic: SV Top Dead Centre  (Read 1115 times)

0 Members and 1 Guest are viewing this topic.

Offline Mikey82

  • Full Member
  • *
  • Posts: 125
  • Country: england
  • Location: England
SV Top Dead Centre
« on: February 14, 2020, 11:02:28 am »
Anyone seen this, Is it useful??
In the Jampot this month


Online camman3

  • Moderator
  • Gold Member
  • ****
  • Posts: 8219
  • Country: gb
  • The more I know, the less I understand......in UK
Re: SV Top Dead Centre
« Reply #1 on: February 14, 2020, 11:17:51 am »
Yes it will work ok, but if you have a C10 (or most SV's), probably just as easy and quick to remove the plug bolt in head (if not rusted in!) and insert rod. :-\
Graham
1957 C12
In sunny (sometimes) Christchurch, Dorset, UK

Online timsdad

  • Gold Member
  • ****
  • Posts: 7877
  • Country: england
Re: SV Top Dead Centre
« Reply #2 on: February 14, 2020, 02:03:03 pm »
If the plug over the piston is stuck fast, it's a lot quicker to slip the cylinder head off a side valve than it is to knock the guts out of a sparking plug. You can then put a straight edge across the top of the barrel to set the timing and also fix the siezed plug ready for next time.


Ray
Just a motorcyclist.

Online Owen

  • Administrator
  • Gold Member
  • ****
  • Posts: 8300
  • Country: england
  • Solutions not problems
  • Location: Chandlers Ford, Hampshire
Re: SV Top Dead Centre
« Reply #3 on: February 14, 2020, 04:24:21 pm »
This does not allow for any leaks on the valves/seats.
1940 C12 (350cc)
1945 C10 & C11
1953 C10 & C11

Offline BSAc11g

  • Full Member
  • *
  • Posts: 609
  • Country: au
Re: SV Top Dead Centre
« Reply #4 on: February 14, 2020, 10:30:33 pm »
There is only one way to accurately determine TDC and that is with a piston stop & timing disc.
Anything else is just wasting time , effort & money.
However people are the stupidist life forms on the planet and just always must have a different way to do everything .
Bike Beesa
Trevor

Online timsdad

  • Gold Member
  • ****
  • Posts: 7877
  • Country: england
Re: SV Top Dead Centre
« Reply #5 on: February 15, 2020, 08:38:21 am »
You're being unfair, I think, Trevor, unless you include yourself.

It's quite accurate enough to time an old clunker by measurement on a rod through a hole in the head, or by measuring to a straight edge across the barrel. When BSA recommended it, they knew these old bikes were designed to be quite forgiving and a degree or two either way wouldn't matter that much. Owners soon learned that the bikes ran better if a bit of trouble was taken to get things right.

Apart from a Goldie, of course, where the timing disc and piston stop method is recommended and clearly described in the bike's original hand book.


Ray
Just a motorcyclist.

Offline BSAc11g

  • Full Member
  • *
  • Posts: 609
  • Country: au
Re: SV Top Dead Centre
« Reply #6 on: February 15, 2020, 10:11:20 am »
You're being unfair, I think, Trevor, unless you include yourself.

It's quite accurate enough to time an old clunker by measurement on a rod through a hole in the head, or by measuring to a straight edge across the barrel. When BSA recommended it, they knew these old bikes were designed to be quite forgiving and a degree or two either way wouldn't matter that much. Owners soon learned that the bikes ran better if a bit of trouble was taken to get things right.

Apart from a Goldie, of course, where the timing disc and piston stop method is recommended and clearly described in the bike's original hand book.


Ray

No Ray I am being FACTUAL.
Piston stops & timing discs are the only ACCURATE method.
All other methods are just good enough for the purpose at hand.
FWIW I use a timing stick myself on most side valve singles because timing is not all that critical, although doing the job very accurately will usually leave you with a better running bike.
Weather the amount of the "improvement" is worth the effort is of course another question all together.

The twins always get timed with a disc because often you have to compromise between the cylinders as most cam rings are not ground all that well & some of the actual valve cams I have come across over the years were not spot on either.

However going to all that effort to make a silly frail tool is not what one would call a valuable use of ones time.
It might be sort of handy on bikes that do not have clean access over the top of the cylinder & I have no experience with anything other than the motorcycles with the correct 3 letters on the tank.
Bike Beesa
Trevor

Online ROB KEMP

  • Full Member
  • *
  • Posts: 333
  • Country: gb
  • Location: ATTLEBOROUGH NORFOLK
Re: SV Top Dead Centre
« Reply #7 on: February 15, 2020, 12:26:10 pm »
Depends if you want it right or near enough .but to be honest you time something like one of our old singles fairly close  and still find the ignition timing needs a final tweek once its running ,nothing on our bikes is 100% precise . my triumph 5t I put better cams in and spent nearly a whole sunday setting the valve timing with 3 keyway timing gears .

Online Owen

  • Administrator
  • Gold Member
  • ****
  • Posts: 8300
  • Country: england
  • Solutions not problems
  • Location: Chandlers Ford, Hampshire
Re: SV Top Dead Centre
« Reply #8 on: February 15, 2020, 12:52:46 pm »
Given the basic nature of the C engines. Using a timing disc is way over the top especially given the wear the engine and ignition has probably got over the years.
1940 C12 (350cc)
1945 C10 & C11
1953 C10 & C11

Online timsdad

  • Gold Member
  • ****
  • Posts: 7877
  • Country: england
Re: SV Top Dead Centre
« Reply #9 on: February 15, 2020, 01:06:48 pm »
Only nearly a whole Sunday, Rob? I hate to think how much time I spent timing the cams up on my Triton, new cams and new, unmarked alloy timing gears  - but none of it wasted.

I timed my Thunderbird with a disc, the same disc as I used on my Goldie back in the late '60s and got free in a glossy magazine at the time. It must be good - it's got Paul Dunstall's name printed on it. The rotor was then marked so I can now use a timing light. I have to run an '012" gap on the right hand points and a '016" on the left to true up the cam because it's still got the old Lucas points fitted by the factory in 1966, with no independent adjustment on the base plate. Works for me.

It's horses for courses because, as has been said, these old clunkers don't benefit from anything other than a rod through the hole and that's why BSA gave the measurement in inches before top dead centre, and not in degrees. That works for me, too. Modern fuels can also benefit from a tweak on the timing, as can the jetting.


My comment was just in reply to your remark, Trevor, that people, I presume on this site, 'are the stupidest life form on the planet' because they don't time their old C with a timing disc instead of a measuring rod through the head as BSA recommended. And I've got a drawer full of silly frail tools that I've made and still occasionally use for whatever. We can waste our time however we like - I've got an ology in it since I retired!


Ray
Just a motorcyclist.

Online Tman

  • Silver Member
  • ***
  • Posts: 2560
  • Country: england
Re: SV Top Dead Centre
« Reply #10 on: February 15, 2020, 01:16:45 pm »
I rather doubt that most those poor sods who only had a C to chug to work and back in the 1940s/50s/60s and had to do the weekend maintenance parked out the front of their houses even knew what a degree disc was, let alone had one.
These work-a-day BSAs weren't built with that level of accuracy (that a degree disc is needed) let alone after 60+ years of wear, repair and general bodgery.
Such precision isn't retrospective.

Online ROB KEMP

  • Full Member
  • *
  • Posts: 333
  • Country: gb
  • Location: ATTLEBOROUGH NORFOLK
Re: SV Top Dead Centre
« Reply #11 on: February 15, 2020, 04:14:40 pm »
This just remined me of all the weekend mechanics who pulled their car to pieces on a Saturday then sh#t theirselves by sunday lunch because because thier cars wouldn't restart .They could change an engine or clutch etc but couldn't understand timing and firing orders .I used to earn good pocket money sorting it out for them .

Offline BSAc11g

  • Full Member
  • *
  • Posts: 609
  • Country: au
Re: SV Top Dead Centre
« Reply #12 on: February 15, 2020, 09:03:13 pm »
[quote author=timsdad link=topic=13403.msg116420#msg116420 date=1581772008

My comment was just in reply to your remark, Trevor, that people, I presume on this site, 'are the stupidest life form on the planet' because they don't time their old C with a timing disc instead of a measuring rod through the head as BSA recommended. And I've got a drawer full of silly frail tools that I've made and still occasionally use for whatever. We can waste our time however we like - I've got an ology in it since I retired

Ray
[/quote]

Ray obviously I have not expressed myself as well as i thought I was doing.
Stupidity  is not how you set the timing on a C
It is spending 1/2  day making a tool that would be no more accurate than a skewer down the plug hole, would be highly unlikely to work properly in the first place and require the tool to be tested for air tightness before& during every use.
I was retired then went to the wall in the GC so now at 67 am finally pursuing the career ( sort of ) that I actually wanted to do back at age 14 by becoming a small engine mechanic. I pressure test 100's of hand held engines every year, and keeping the pressure testing gear in good condition and checking that it is not leaking while you are doing the testing takes nearly as long as the test.
Secondly the "tool" requires no leak down inside the cylinder to actually work.
Unless you are using gapless rings that situation does not and can not exist inside a motorcycle engine.
At the speeds that you are turning the engine over to find TDC without overshooting most of the  gas inside the combustion space will leak down past the rings which as you should know do not actually make an air tight seal when moving slowly.
This is one of the reasons why engines with reducing compression are difficult to start.
If you have a leak down tester ( I have 3 ) shove it in the plug hole then slowly turn the engine over and watch the gauge move.

Then double stupidity is actually publishing the story about it with construction details .

Sorry to be so pesnickerty but there are thousands of people out there who make thousands to millions every year.
They have no technical expertise in what they do other than to have an amusing or sexual presentation technique.
They are called "Influencers" and literally billions of people rely upon them to make up their (lack of ) mind about what they buy because they are too lazy ( stupid ) to actually think about what they purchase.

You are definately one of the people on this list with more than sufficient mechanical knowledge to have looked at that lump if idioticy and thought
"How does this work " & " what will prevent it from working properly"
However it looks like you got no further than the initial "that's different".

I trained in engineering ( metallurgy to be precise ) so I look at everything with an engineers eye.
What can go wrong with it
What are the consequences of it going wrong
As such the phneumatic TDC finder is about as useful as double sided toilet paper.
Bike Beesa
Trevor

Online hampshirebiker

  • Gold Member
  • ****
  • Posts: 5906
  • Country: england
Re: SV Top Dead Centre
« Reply #13 on: February 15, 2020, 09:10:13 pm »
I never realised that top dead centre could be this complicated. Yes a disc is more accurate (and I use one), but on a "C" it's not that critical. In times gone by many handbooks described the basic setting and recommended fine adjustment following a road test.
Postal - Liphook Hants - But just into West Sussex.

Offline Mikey82

  • Full Member
  • *
  • Posts: 125
  • Country: england
  • Location: England
Re: SV Top Dead Centre
« Reply #14 on: February 15, 2020, 09:22:57 pm »
I did the take the cylinder head off and measured down and got the timing right, and I saw a video that turned the distributor to improve tickover, which made no difference for me.....
I agree with Tims dad take the top off (can be done without removing he petrol tank) this is the best way to do tdc..
Lots of clever ideas but the oldens are the ones that work...
With the amount of knowledge on this forum I,m sure a manual could be written with the solutions and settings for these bikes, and make a few dollars in the meantime....