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.

Finnkai
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Sorry about the delay but

Here's a long overdue update.

As suggested, I measured the thread size of the new sprocket obtained from Australia and confirmed (as suspected) it is metric 16mm with a 1.5mm pitch. Whereas for my machine I needed a sprocket with a 5/8" UNF 18 turns per inch thread to fit. 

Having looked up the Tables for the metric and imperial thread sizes, I established the tap size drill for a 5/8" UNF screw would be 14.5mm diameter which is virtually the same as the tap size drill for a 16mm metric screw (which can be between 14.5mm and 15mm with the larger diameter drill recommended for tapping a thread in steel where the thread depth can be less deep).  The thread pitch of UNF 18TPI is 1.4mm compared to the 1.5mm pitch of the metric thread.  I also contacted the Australian supplier who sympathised with my predicament but could only suggest I purchased a new cylinder (with a compatible metric thread on the spindle).  You can imagine this did not appeal especially as I had invested much time and some funds in renovating and sharpening the original cylinder!

The upshot is that I eventually decided to try re-tapping the sprocket on the grounds that, even it that didn't work, I had little to lose.  When I did this I fopund that the threaded section of the "boss"  part of the sprocket gives way to a void space (between where the larger and smaller sprockets are attached) so I was able to recut the thread right down its whole length (see photo).

Replacement (L) and original (R) Morrison sprockets

I have now successfully fitted the replacement sprocket onto the cylinder and reinstalled the cylinder/blade assembly on the mower.  The sprocket was a little tight but seemed to go on alright and I was able to tighten it all the way down so the two sprockets lined up correctly and the respective drive chains ran straight.

I then reinstalled the 4hp Briggs & Stratton engine with its completely reassembled and cleaned carburetor (plus a new pump diaphragm and a spotless fuel tank) and managed to start up the mower and run it briefly for the first time.  The cylinder span freely, albeit not under any load.  That was quite a moment!  The engine seemed to run OK-ish (no horrible noises).  I then drained the engine oil and replaced it with new.  It was a bit reluctant to start after this although did eventually. 

My impression was that the engine compression was rather low so I have decided to take a look at the valve clearances (up till now I had not even had the head off as I had concentrated on the mower itself).  The piston and cylinder bore look fine although the valves are a bit sooty.  The intake valve clearance was a bit lower than the B&S spec at around .004" compared to the spec of between 0.005"-0.007".  The exhaust valve clearance seems OK.  My plan is to lap the valves and do any minor resetting of valve clearances and then try the engine out again.  Maybe treat it to a new spark plug too.  My aim is to get it to the point where it starts and runs reliably and (of course) cuts grass effectively with its newly sharpened blade.

Thanks for all the encouragement and help along the way,  Hopefully not much further to go now.

hortimech
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Glad you got it sorted.

Glad you got it sorted.

Now, as for the 'low' compression, it should seem low, it is fitted with compression relief, so you cannot test it with a normal compression tester and when you pull the engine over, there is no way to tell if the engine is okay or not. Briggs & Stratton make a tester, this works by letting compressed air into the cylinder, locking it off and seeing if it holds the pressure. You cannot lose anything by regrinding the valves, but there may be no need to.

Finnkai
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Thanks Hortimech.  I didn't

Thanks Hortimech.  I didn't think my engine had compression release as the components for it are not shown on the Briggs parts manual.  It's an 112232 0839 4hp engine manufactured in 1988.  I will take another close look and make sure I measure the valve clearances with the piston 1/4" past top dead centre (as per Briggs website) just in case.

hortimech
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You would have to strip the

You would have to strip the engine down to find the compression relief and then you probably wouldn't see it. It is all down to the profile for the exhaust valve. this is ground in such a way, that it opens the exhaust valve to release the compression at starting, but has no effect when the engine is running.

 

Finnkai
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Oh, I see.  I had imagined it

Oh, I see.  I had imagined it was a mechanically driven (centrifugal force) device that deactivated as revs increased.  I'm still learning!

hillsider
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If you spin the engine

If you spin the engine backwards you should be able to feel full compression as the decompressor profile is only ground on one side of the cam lobe. I may be corrected here but I believe the 'bump' momentarily lifts the inlet valve. The theory is that it allows some leakage at cranking speed but at operating speed the the effect is negligable as hortimech has said in his post. 

wristpin
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All good information so far

All good information so far particularity checking and setting the valve gaps with the piston 1/4" down past TDC on the power stroke - get that wrong and grind too much off  and the engine will "bite"!

The reverse rotation compression  test is much easier to carry out on a rotary mower with the blade in place or even on a Marquis with Ransomes heavy clutch flywheel . Not quite so easy or decisive in your situation. We were an early adopter of the pressure tester that Hortimech mentions, now commonly referred to as a Leak Down Tester and a very useful diagnostic tool. Briggs introduced it to the "mower trade" and at the time it was a bit of an extravagance but now versions are widely available on the internet and within the budget of the home mechanic - assuming the availability of a compressor.

 

The early version of the Leak Down Tester - for convenience coupled to its own water trap and pressure adjustment / gauge.

Finnkai
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Wow.  That's some piece of

Wow.  That's some piece of kit.  I did examine my engine closely and believe I can feel a momentary bump on the exhaust valve as the piston comes up to TDC (as I think Hortimech explains). 

Having cleaned and lapped both valves, I took a very small amount off the inlet valve (measuring with piston 1/4" past TDC) to restore it to the low end of the clearance specified for my engine.  Refitted cleaned head with new gasket and torqued bolts carefully to 140 inch pounds.  New spark plug too.  Plan to check coil resistance and armature gap before refitting engine to carb and mower to ensure best spark possible.  Will report back on hopefully improved starting and running performance.