Morrison Olympic 600 cylinder drive sprocket

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Finnkai
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Morrison Olympic 600 cylinder drive sprocket

In earlier post I mentioned I had foolishly damaged the teeth on the double sprocket that screws on to the end of the cylinder shaft in my efforts to remove it.  I have sourced a (genuine Morrison) replacement sprocket from a dealer in Australia which arrived yesterday.  It looks identical to the one I'm replacing.  However when I screw it onto the shaft it becomes very stiff after a couple of turns and I have come to the conclusion the thread pitch is slightly different.

My options seem to be to force it on - effectively recutting the threads using the shaft; to take it somewhere and get it re-tapped with the right thread (NB it's left hand thread); or abandon my investment in this new part and seek some other solution. The part cost around £60 so you can imagine the last option is not attractive. Apart from this I have also refurbished the rest of the machine and had the cylinder and blade re-sharpened.

Thoughts?

hortimech
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Does the old one screw on

Does the old one screw on easily ? if not it could be damaged threads on the end of the cylinder and you can clean these up with a thread file.

If it does screw on, then I doubt if you will be able to force the new sprocket on, you will just destroy the threads in the sprocket and on the shaft. If it is just damaged threads in the new sprocket (has been known) then you may be able to clean these up, if you can find a suitable tap or somebody with a metal lathe that knows how to recut internal threads.

If the thread types are different, one imperial, one metric, then you will never get them to screw together. 

Finnkai
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The old one does screw on so

The old one does screw on so don't think it's damaged. The new one starts ok and gets progressively stiffer after a few turns.  The difference in threads does not seem to be large. I have emailed Masport (Morrison) in New Zealand to see if they can advise but past experience is they have little info on these older machines.

wristpin
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Sounds as though there maybe

Sounds as though there maybe a mismatch in the thread pitch. Trying to force it on is likely to end in disaster as the mismatch will be magnified by any additional rotation. Hopefully Masport will advise re any running changes to the threads.

If you bought the new sprocket by part number it may be possible to compare numbers with the appropriate parts book for your machine but there's always the possibility that the seller identified it by shape and was unaware of any specification changes.

In the worst situation is there any possibility of cutting the threaded boss off each sprocket and welding the old boss to the new sprocket teeth.

Finnkai
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I bought it from its

I bought it from its description on the dealer's website. The picture and number of teeth matched and the part number was from a spares manual for the same type of machine (albeit 2008 not circa 1990).

Will see what Masport say. Guess it's possible the new sprocket has damaged internal threads. Unfortunately sending back for a refund/replacement difficult with dealer in Australia! Should have bought the more expensive part from their UK agent.

If that is case, I think I will investigate getting threads cleaned up/re-tapped before re-welding the new small sprocket to the old boss.  But will depend on finding someone with the right skills locally for either job.

Oh dear. Life is never simple.

wristpin
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Thread gauges are not

Thread pitch gauges are not expensive . I'm guessing that the threads in question will either be UNF or metric so you only have to buy one set to see if there's a fit on one component but not the other. If it were not for them being  left handed you could just lay a bolt along side the threads as a comparison .

https://simplybearings.co.uk/shop/product_info.php?products_id=780045&va...

Finnkai
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Thanks. Good idea and a

Thanks. Good idea and a useful tool for the future. Am currently away but will purchase and investigate on my return.

I am increasingly wondering whether it is not a case of thread damage in the new component. It just seems odd to change something like that when everything else in that part of the mower is the same. I guess we'll see.

hillsider
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As suggested by wristpin a

As suggested by wristpin a thread gauge is definitely the way to go, these folk do a full range of Left hand taps and dies so you can check the diameters and threads per inch from their listings.

http://www.tracytools.com/taps-and-dies

 

 

Finnkai
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Have now found an Australian

Have now found an Australian website/community (Outdoorking.com) with a parts list for old Morrison "reel mowers". The part no. is identical to the one I bought. I think therefore I have been sent a defective item.  Will make a few more inquiries but if I'm right will see if can get the supplier to replace.

Will still get the pitch gauge though. And may also investigate re-tapping.  Thanks.

wristpin
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As you may know, your

As you may know, your Morrison is a version of the Ransomes Marquis made under licence. I say version as Morrison altered the Ransomes design in several areas, the dual cylinder  sprocket being one of them. The original Marquis had imperial bearing on the cutting cylinder which were later changed to metric ones. I t occurs to me that there is an outside chance that Morrison did the same.

It just so happens that Im in the middle of a full nut and bolt overhaul of a "metric Marquis" and also have a similar Imperial unit on the shelf so out with the thread gauges . The Imperial measuring a pitch of 1.8 and the metric 1.5 but just to prove that it was a total waste of time either sprocket screwed onto either cylinder with no force required!

I suggest that you check the cylinder bearings to ascertain whether metric or imperial and then apply the appropriate pitch gauge ; then apply that to the sprocket . If a visual inspection of the inside of the sprocket does not show any obvious damage I'm inclined to think that it is a mismatch of threads rather than damage. Obviously take into consideration that, in trying to fit it, you may have damaged the first couple of threads in both.

In the case of the metric Marquis the cylinder and rear roller bearings are metric but the top shaft outer and spigot bearings are still imperial,  so in ascertaining the status of your machine check the cylinder itself rather than make an assumption based on the bearings elsewhere on the machine.

hortimech
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I think you may have a 'bitsa

I think you may have a 'bitsa' machine there Wristpin. I am very sure that when Ransome went metric, bearing wise. they changed all the bearings. So your flywheel and top shaft assembly are probably from an earlier machine..

Finnkai
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Thanks for these further

Thanks for these further thoughts. If they did follow Ransomes and change the pitch to metric, would they have kept the same part number?

Also would the part fit for 2 or 3 turns before getting stiff?

I did fit new cylinder bearings after the sharpening so will check what size they were when I get home.

Thanks again for the good advice.

wristpin
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Too many loose ends! We need

Too many loose ends! We need to determine a "known".

Does your manual make any reference to metric or imperial bearings or hardware? If so does your machine agree with that. So if the book says metric with the part number that you've bought and the bearings are metric ( in the metal) you have a matching set. If anything doesn't agree we can then work out which is the " odd man out"

wristpin
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Hortimech. Yes it is

Hortimech. Yes it is confirmed as a bitza ! I've dug out a parts book that covers the Mk 5 and 5M  20" and 18" machines. The 30" is shown as being available with either a BS or Villiers lump and the 18" with BS only. Interestingly the illustration of the 20" engine platform actually shows the multiple fixing holes for the choice of engine - as per mine. So mine must have started life all metric with a Briggs but at sometime acquired a taper crank Sloper with a matching clutch flywheel and top shaft. 

Finnkai
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Hi Wristpin,  I agree I need

Hi Wristpin,  I agree I need to establish with greater certainty exactly what is going on.

I have ordered the thread gauge and will measure the pitch on my cylinder shaft end as soon as possible next week when I return home.

I have also just received a very helpful reply from an engineer at Masport New Zealand explaining that, after a period of obsolescence, the sprocket was reintroduced as a spare part in 2008 with what appears to be the same part number.  He sent me the engineering drawings which clearly show the thread spec as M16x1.5 (i.e. metric).  I have emailed him to ask whether the original "old part" had an imperial thread and await his reply.

Once I work out how to do it I will post the 2 drawings (.pdf files) as they may be of wider interest.

Will update again next week when I have a more complete set of facts.

wristpin
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Well, that's gold dust!

Well, that's gold dust!  Metric 1.5, exactly the same as I measured on my metric Marquis. Hurry home and measure that cylinder, I've a horrible feeling that it will be 1.8.

Finnkai
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Just had the reply from

Just had the reply from Masport engineer.  He has now sent me the drawing of the original cylinder spindle which shows the thread was 5/8 UNF 18TPI LH. So it looks like you are right.  They changed from UNF to metric but kept the same part number.

What to do next? First I will measure my thread expecting it to be UNF. If so, I feel that it might be worth trying to re-tap the metric sprocket although I appreciate that may not work. If that doesn't work, I think the next option is to try and find someone who can weld the small sprocket from my replacement part onto the boss of the old one.  I am reluctant to throw away my investment and don't think there is any chance I'll get a refund from Australia. I did establish that Masport's UK dealer has a few of these sprockets. (I didn't buy from them as the Australian supplier was cheaper even with shipping.) So I might also call and ask them to check if by any chance the ones they have are UNF.

I will need to buy a tap to attempt option 1. On the Tracy tools site there are several different types available - "taper", "second", and "plug". I am not sure which of these would be best. Thoughts?

 

Finnkai
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Just had the reply from

Just had the reply from Masport engineer.  He has now sent me the drawing of the original cylinder spindle which shows the thread was 5/8 UNF 18TPI LH. So it looks like you are right.  They changed from UNF to metric but kept the same part number.

What to do next? First I will measure my thread expecting it to be UNF. If so, I feel that it might be worth trying to re-tap the metric sprocket although I appreciate that may not work. If that doesn't work, I think the next option is to try and find someone who can weld the small sprocket from my replacement part onto the boss of the old one.  I am reluctant to throw away my investment and don't think there is any chance I'll get a refund from Australia. I did establish that Masport's UK dealer has a few of these sprockets. (I didn't buy from them as the Australian supplier was cheaper even with shipping.) So I might also call and ask them to check if by any chance the ones they have are UNF.

I will need to buy a tap to attempt option 1. On the Tracy tools site there are several different types available - "taper", "second", and "plug". I am not sure which of these would be best. Thoughts?

 

wristpin
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I am not a time served turner

I am not a time served turner or machinist but I would be concerned about re threading the sprocket in case you end up with a chewed up mess but then there is the fall back position of cutting and shutting . If the shaft is going into a blind hole you will need a plug tap to get to the bottom but possibly a second cut to " open up" with to allow the plug to enter.  However If measuring between the shoulder that the sprocket beds onto and the end of the shaft and transferring that measurement to the blind hole and there is, say, 6mm clearance between the shaft end and the bottom of the hole you might get away with just a second cut.

However, regardless of all the above, and as said in my earlier post , either of my sprockets fitted either shaft, albeit with some slop; maybe the result of poor initial tolerance or maybe some wear and tear, so possibly my doubts about re-tapping are a bit ott.

hortimech
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Not sure if you will get away

Not sure if you will get away with trying to retap your sprocket, 5/8" is the same as 16mm. Fairly sure you will end up with a mangled internal thread if you try it.

As for the taps, 'first taper' is what it says, a tap with a taper, this taper is greater than the taper on a 'second taper' tap, finally a 'plug' tap is a straight tap. You would normally tap a new thread with the 'first  taper' tap, move up to the 'second taper' and finish off with the 'plug' tap.

If you do try to retap the sprocket, you are going to have to open up the blind end, either of the taper taps will not reach the bottom and the plug tap will probably not even start.

I still think the best way out of this (if you cannot find the correct sprocket assy) is to obtain two blank sprockets (bearing supplier ?) and then get an engineer to turn of the old ones, machine the new ones to fit and weld them on.

Finnkai
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Thanks for your thoughts.

Thanks for your thoughts. Will reflect on them carefully.  I am clear that whatever action I take must not risk making the problem worse. If I knew or could find someone who would take on the machining/welding suggested, I agree that may well be best solution - especially as only one of the two sprockets is damaged. Will update you when I get home next week.