square 4 advance retard mechanism

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MARK.WALSH
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square 4 advance retard mechanism

Postby MARK.WALSH » Sun Dec 02, 2018 3:04 pm

Dear all
as promised on a different thread/topic I had a look at my cam on my distributor today to see if there was any discernible wear - there was none I'm pleased to say.
Looking at the mechanism more closely with the baseplate removed, I noticed I couldn't make the bob weights swing out when turning the cam by hand.
I then removed the centre screw and looked at the pivots on removing the cam - Nothing was seized. On replacing the cam the bobweights could now be made to swing out but as soon as d the centre screw was replaced everything locked up again. There also doesn't seem to be a spring washer in the system (drags exploded diagram shows one)
Question is - should it all be tight when the screw is replaced, would the spring washer make a difference?
Any thoughts - knowledge
Mark

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keith.mettam
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Re: square 4 advance retard mechanism

Postby keith.mettam » Tue Dec 04, 2018 8:26 pm

Mark, having worked on many old cars with distributors over the years the cam should be free to rotate on the shaft when the screw is tight. It should not bind at all or the timing advance/retard will be affected. I imagine that the missing spring washer is no larger than the diameter of the distributor shaft and will make a difference when fitted, i.e. it will prevent the cheese head screw from coming loose but will also give the clearance between the head of the screw and the cam so that the cam does not bind, the wider screw head keeping the cam correctly located on the shaft. It is likely that the cam will have some discernible up and down play when properly fitted. I am not a Square Four owner but it is clear to me that the cam should not bind when that screw is tight. All the best, Keith.

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paul.jameson
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Re: square 4 advance retard mechanism

Postby paul.jameson » Tue Dec 04, 2018 8:37 pm

Hello Mark,
Having recently rebuilt the distributor for the Healey and having been a little unhappy whether I would get full advance, I tried it out, using a screwdriver in the rotor arm slot to gain the advance against holding the drive gear in the other hand. On my distributor, it makes no difference whether the screw is tight or loose as to how much advance you get. The possible amount of advance is the same. There is no spring washer under the screw on the (ex Mk I) distributor I am using and there wasn't one on the distributor that came with the bike either. Nor can I find one on the exploded diagrams so I don't think there should be one.
Paul Jameson
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser.

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simon.holyfield
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Re: square 4 advance retard mechanism

Postby simon.holyfield » Tue Dec 04, 2018 8:56 pm

There's clearly something amiss Mark. You can do that screw up as tight as you like and the cam is still free.

A thought - its a special screw. Have a look at this blog post:

http://ariel-square-four.blogspot.com/2 ... egins.html

Does your screw look like that? The 25D4 distributors used on Minis and Morris 1000's use screws like that too - it's to pass oil to the bushes. Maybe there is some other element that provides clearance for the cam in some way.

If you are still struggling come Friday I will take mine out for a picture and a proper look.
cheers

Simes

'51 Square Four, '58 Huntmaster, '42 W/NG, http://ariel-square-four.blogspot.com

MARK.WALSH
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Re: square 4 advance retard mechanism

Postby MARK.WALSH » Wed Dec 05, 2018 5:17 pm

Keith / Paul / Simes
thanks for the help and advice
clearly something wrong and Drags show the washer to be 185021 on their website. Paul interesting that your washer is not present but the shafts aren't locked. Simes I have the proper screw with the oil hole in the centre but I think Keith is right about the washer giving extra height to the screw head to stop it binding on the cam part of the shaft.
I will investigate further over the weekend - (these cold dark nights are not conducive when it comes to working on bikes when you get home from work)
- all this might explain that slight hesitation I get from the bike at around 45 - 50mph!

Either way sure I will sort it - thanks again all
Mark

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paul.jameson
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Re: square 4 advance retard mechanism

Postby paul.jameson » Wed Dec 05, 2018 8:04 pm

I have checked again and there is definitely no washer on either the Mk I distributor I shall use or on the fire damaged one built by Healeys about 1975 and not dismantled until about a month ago. There is a lip inside the cam which appears to be tapered downward from the outer edge to the central hole. Unless a washer was too small in diameter to catch on this lip, it would tend to prevent rotation when screwed up too tight. With the central screw tight, I do have slight up and down movement on the cam which I consider healthy.
Paul Jameson
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser.

MARK.WALSH
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Re: square 4 advance retard mechanism

Postby MARK.WALSH » Sat Dec 08, 2018 5:00 pm

Checked things over thoroughly today and without a doubt I can only tighten up the centre screw if I have a washer/spacer of some kind to stop the two shafts binding.
I tried a cut down spring to act like a washer - better, but still binding a bit. Now I've tried a very small section of copper brake pike as a tubular spacer / washer. Loads better but cant understand why it should be binding in the 1st place if all parts are original.
Now it works I will leave it alone
By the way tried it for a test run. I think the hesitation I get at 45ish has reduced but the bike normally runs better on cold winter days so it might be summer before I can gauge any significant advantage
Thanks for all your help guys
Mark


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