Technical Questions: 1928 Model C

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john.whiting
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Re: Technical Questions: 1928 Model C

Postby john.whiting » Sun Apr 16, 2017 2:49 am

I say "Good on yer" for trying it.My only advice would be to Loctite everything that can possibly unscrew or fall off.Regards John.

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Re: Technical Questions: 1928 Model C

Postby cmfalco » Wed Apr 19, 2017 6:12 pm

Having now gone through the ~90 posts in the 'Which pistons' thread without finding a single actual measurement of the weight of any piston (as opposed to words like "heavy") I'm beginning to wonder if this is the right place to seek technical information. However, hope springs eternal that someone has the answers to at least a few of the questions I posted at the start of this thread.

For what it's worth I got word from the shipper today that my Ariel will leave England on Friday so it should be to me by the end of next week.

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Re: Technical Questions: 1928 Model C

Postby john.whiting » Thu Apr 20, 2017 11:34 am

If you want that kind of detail on a 1928 motor,you will have to write the book yourself.Regards John.

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Re: Technical Questions: 1928 Model C

Postby Simon.Gardiner » Thu Apr 20, 2017 2:08 pm

I'm not sure that the exact weight of a piston is as important as the size and clearance - I've seen manufacturers' published dimensions much more often than any published weights.(I could possibly expand quite a lot on why the meat of a discussion about pistons might only refer to 'heavy' and 'light' weights, having spent a lot of time trying - unsuccessfully! - to get 'light' pistons for my Huntmaster....)
I'd suggest that values like con-rod length and balance factor are also 'nice to know's not 'need to know's - which may be why they're not often found, along with a lot of other information!)

SG
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)

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Re: Technical Questions: 1928 Model C

Postby cmfalco » Thu Apr 20, 2017 5:31 pm

Simon.Gardiner wrote:I'm not sure that the exact weight of a piston is as important as the size and clearance ... I'd suggest that values like con-rod length and balance factor are also 'nice to know's not 'need to know's - which may be why they're not often found, along with a lot of other information!)
The con rod length would be 'nice to know' because if I knew it I could calculate crankshaft rotation vs. piston position BTDC. That is important for getting accuracy and consistency checking the cam and in timing the magneto. It's true that piston weight and balance factor aren't easily found. But, that's not because these factors aren't important, which they are, it's because in the old days they were "irrelevant" because mechanics simply replaced scuffed pistons with new ones from the manufacturer so the balance factor didn't change. Unfortunately, with those parts no longer available we have to use aftermarket replacements whose weights differ significantly.

Quoting Phil Irving in 'Motorcycle Engineering' on why the balance factor is important: "Usually, a balance factor of 60-65 per cent, will be found to be correct, but it may vary widely; the factor for the MOV Velocette was as high as 85 per cent., while some engines have been down to 40 per cent... Because the eventual smoothness obtained depends so much upon the frame, a balance factor which suits one installation may not suit another... An instance of this was found in the original Vincent-H.R.D. singles. These engines ran very smoothly in the standard spring frame with a factor of 66 per cent., but the speed way versions, of which a very few were made, vibrated badly in a cobwebby dirt-track frame until the factor was reduced to 61 per cent., this not-very-large reduction making all the difference between a machine which was passably smooth and one which shook itself out of your hands."

Another quote showing that a few percent matters comes from A. Golland's 'Goldie': "Balance factor up to the year 1954 was 55%, but thereafter, 58 % was found more suitable..." That was the year Gold Stars changed from a plunger to a swinging arm frame.

If I were only to use my Ariel for short club runs the extra vibration caused by having the incorrect balance factor might not matter. But, on a 4000-mile ride having unnecessary extra vibration not only would be uncomfortable it also would degrade the reliability of the bike.

john.whiting wrote:If you want that kind of detail on a 1928 motor,you will have to write the book yourself.
That thought has crossed my mind. I did write a book on Gold Stars (now in its 5th edition), but the amount of information on Black Ariels makes that about Gold Stars seem copious by comparison. Despite that, a shop manual might emerge from all of this, which would be of interest to roughly three other people...

To summarize, I'm not interested in answers to the questions I posed just to write in a notebook. They are important to the proper rebuild of a motorcycle that needs to be reliable for 4000 miles with minimal maintenance during that two-week period.

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Re: Technical Questions: 1928 Model C

Postby Eero.Korhonen » Fri Apr 21, 2017 5:23 am

It is great to see Ariel in Cannonball Rally, I have always check pics and videos.
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Ariel VH 1954, IZH 350 1962, H-D Sportster Hugger 1992, AOMCC Member 133

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Re: Technical Questions: 1928 Model C

Postby john.whiting » Fri Apr 21, 2017 9:53 am

In fact,you will find out all these details and more besides,when you strip your motor and gearbox,and check everything before reassembly.Dont forget the wheel bearings,as they will be tapered rollers of a size long obsolete,and not easily replaceable.I prefer to sanblast the frame as all dodgy repairs and faults show up plainly.An ultrasonic check of frame and fork wall thickness would also be advisable,if corrosion damage is evident anywhere.Never trust the work of a restorer to be done correctly.Another point is the obsession with engine balance,and clutches way out of balance from wear never even considered.If I was doing this run,I would use my 28FD,and have a high expectation of finishing without problems.And have a comfortable seat as well.Regards John.

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Re: Technical Questions: 1928 Model C

Postby Simon.Gardiner » Fri Apr 21, 2017 12:07 pm

cmfalco wrote:.....important to the proper rebuild of a motorcycle that needs to be reliable for 4000 miles with minimal maintenance during that two-week period.


That you won't be doing a little club run is appreciated, believe me.

There's more than piston weight involved in balance factor. You might have a piston that weighs right and a con-rod that doesn't (I've got at least one of those for the BM) - there are manufacturing tolerances and then what was allowed out of the gates because it didn't look too bad (again, I've got some genuine Ariel spare parts that are way out of wack).

To be sure of getting a balance factor at an exact percentage you will have to balance the assembly wot you got - and although it would be nice to have the original manufacturer's figure as an initial target I'd suggest (and I have read Phi Irving) it might be exceptional to find that if you're not on the sweet spot of the exact percentage the whole plot will vibrate to pieces - there are some threads with a discussion of balance factor with regard to the single-cylinder bikes (although I don't think they go back to the 'black' models).

And do you really need the con-rod length to arrive at the 'working' settings for valve and ignition timing??

SG (about to start re-reading Phil Irving... :) )

(PS I do envy you the adventure!)
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)

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Re: Technical Questions: 1928 Model C

Postby MBolton » Fri Apr 21, 2017 2:31 pm

Had a quick look on Amazon and the 5th edition of the Gold Star Buyers Guide is still available. The "look inside" feature on Amazon shows what a splendid book it is. If I had or was looking for A Gold Star I would buy the book. Good luck in your quest for information and in the cannonball run.

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Re: Technical Questions: 1928 Model C

Postby iansoady » Fri Apr 21, 2017 4:27 pm

If you take the con rod length as double the stroke that would normally be pretty close to reality and given all these old engines are quite individual it's probably likely to need adjusting anyway.

I actually wrote a little VBA form to calculate inches / mm before TDC from degrees and vice versa, and did find that (within limits) con rod length had little effect.
Ian
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