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Marine Engine Flywheel Fixing

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Ramon Wilson18/01/2021 14:04:14
1052 forum posts
205 photos

Hi, does anyone know how a flywheel would have been retained in place on a full sized compound marine engine. Keyed yes, but how was it held in position laterally.

Any help or knowledge would be most appreciated but I'm afraid in this instance a grub or set screw simply won't do wink

Thanks in advance - Tug

JasonB18/01/2021 18:16:46
19973 forum posts
2179 photos
1 articles

I seem to recall seeing them drilled for bolts into an integral flange on the end of the crankshaft but could be wrong.

Ramon Wilson18/01/2021 18:40:23
1052 forum posts
205 photos

So the flange is part of the crankshaft then ? That would make sense - drive from a key but held by a bolted flange.

Thanks Jason but if anyone has any full size knowledge too that would be appreciated.

JasonB18/01/2021 18:45:53
19973 forum posts
2179 photos
1 articles

A bit later than what you are working on but shows the flange, flywheel a bit further along the bottom row of photos

David Senior18/01/2021 18:51:46
8 forum posts
5 photos

I've had a quick look through some books on marine steam engines and I can't find any that show a flywheel, but they all appear to have a flange as Jason suggested. I doubt if you would get keyways on the bigger stuff.


MichaelR18/01/2021 19:01:11
409 forum posts
80 photos

Flange fixing marine crankshaft Link


Journeyman18/01/2021 19:33:11
907 forum posts
166 photos

This is the crankshaft end of the triple expansion engine from the TS Glen Strathallan. Long time since I was a cadet on board and can't remember what went where but the flange is there. The picture is in the Science Museum where the engine ended up so they have used the flange with a chain wheel to provide a drive for the display. Cant say I'm impressed by the chain tension!



Edited By Journeyman on 18/01/2021 19:34:18

bernard towers18/01/2021 20:53:32
108 forum posts
66 photos

Our leak compound has a keyed flange on the crank with two M8 socket headed grubscrews screwed through the flange directly over the key. Lateral movement is taken care of by the prop shaft thrust bearing mounted on a keel block.

Paul Kemp18/01/2021 20:56:43
600 forum posts
18 photos

I don't think many decent sized marine steam engines had flywheels, instead they relied on the inertia in the shafting and prop and were flange drive. All the large marine diesels I have worked on have had flange mounted flywheels, no keys just fitted bolts and high torque.

If a flywheel were fitted to a small marine steam engine I would expect it would be secured with a taper gib head key. That's how traction engine flywheels and line shaft pulleys etc were retained, having had to remove some I can vouch for how tight they can hang on! Either that or mounted on a taper on the end of the crank in the same manner shaft couplings are (both with and without keys) the modern type of taper coupling using oil injection to seat and remove are a thing to behold, they can come off with a significant bang and not something you want to be messing with without some restraint in place.


Ramon Wilson18/01/2021 21:11:06
1052 forum posts
205 photos

Hi guys,

Thanks to all for your input on this matter including Trevor's PM. The engine I am building (the 1924 ME published Marine Compound off the John Tom site) is not fully scale but is a design based on full size practices. I'd like to make it as close to full size as possible where I can hence the question.

Making the flange part of the crank seems the way to go but from what I can see so far is that the flywheel bolts directly to the flange and not seating on the shaft itself.

I guess this is one of those areas where near every manufacturer had a variation on a theme. Interesting.

My thanks again - much appreciated


Paul Lousick18/01/2021 21:39:05
1693 forum posts
625 photos

Flywheels were also fitted with 2 taper keys, spaced at 90 degrees to each other on on some early steam engines to give a more secure mounting.


flywheel keys.jpg

noel shelley18/01/2021 21:53:38
390 forum posts
11 photos

In the context of marine use flywheels were not the order of the day, eg the 2500 Ihp triple expansion engine used in the british designed Liberty ships had no flywheel just a flange that was bolted to the shafting. But for stationary use a flywheel may well be used, eg The Dover engine, a triple expasion engine used for water pumping at Forrncett st Mary, near Norwich and still steamed. Noel.

Ramon Wilson18/01/2021 23:13:29
1052 forum posts
205 photos

Paul, Noel, Thanks for this further input.

I have several books I can refer to for stationary engines but nothing that covers marine engines. The design (ME May 1923 not '24 as previously stated) I am working to is described as following "full size practices of a kind of engine fitted to a small coastal steamer". It is shown with a flywheel - which to my mind does look a little large in diameter but that's another matter - it is merely shown keyed to the shaft with no flange or means of retention at the forward end.

As for a flywheel at all - as drawn the cranks are at 180 degrees though the author states it can be built with them at 90. Whether that's the reason for the flywheel is not stated but the Elliot and Garrod 'monkey' triple (two cylinders in line the HP in tandem with the intermediate) had cranks at 180 degrees and had a centrally mounted fairly substantial flywheel that also acted as the central crank web.

I will continue researching - confirmation if one would have actually been fitted now being the first priority, it's fixing method if so now the second.

My thanks again


JasonB19/01/2021 07:05:26
19973 forum posts
2179 photos
1 articles

Ramon, a tapered key and mating keyway would be one way to keep it on the shaft. Text does mention two tapped holes into the end of the (slightly shorter? ) crankshaft and a disc to retain the flywheel. Whether that was usual practice I don't know.

Hard to know if the original may have had a flange and it was just omitted to save having to make split eccentrics as you can't slide them onto the shaft if there is a flange in the way

This is the engine in question for those not familiar with the design, full size was about 8ft tall and 5ft long.


Edited By JasonB on 19/01/2021 07:41:11

Ramon Wilson19/01/2021 07:54:15
1052 forum posts
205 photos

Hello Jason,

Although I read through initially I have to confess to having missed the fixing method in the text and was focusing more on the drawing!! It would work of course but hardly be in keeping I feel. Having said that I spent a long time last night looking at countless images I could find. Most if not all seem to confirm that marine engines rarely had a flywheel. Having said my small collection of books did not cover marine engines I remembered some catalogue reprints I have.

Several feature closely similar compound engine designs - none of which feature a flywheel.

Virtually all model variants appeared to have a flywheel - obviously to help smooth out the reciprocation at the much smaller scale so it looks like a compromise - because I will run this on air I will fit one as such though slightly smaller in diameter to an integral flange as you suggested and what most engines do seem to feature at both ends. I noticed many of them have barring holes in the rim of the larger flange as well so something else to add.

Thanks again for all the input - just what a forum is for yes

Ramon (Tug)

Howard Lewis19/01/2021 12:48:06
4455 forum posts
8 photos

It is quite common for flywheels to be located to the flange by either a dowel, for location rather than a keyway, ( to avoid a stress raiser ) or by fitted bolts, with one displaced so that the wheel will only fit in one angular position.

In marine practice, the shaft and propeller inertia would probably act as a flywheel to reduce cyclic irregularity, probably aided by the hydraulic damping of any torsionals.

With the likely length of the shaft, and the inertia of the prop, the natural frequency would tend to be low.


noel shelley19/01/2021 13:58:37
390 forum posts
11 photos

Gentlemen, REMEMBER, this is a direct drive, reversing engine in a moving vessel that must be able to maneouver, a flywheel will be a REAL handicap. On a non reversing engine the flywheel will help to smooth things out, eg a mill engine.

I worked on a diesel powered vessel. It had a direct drive, reversing, air start diesel engine of 500hp, the flywheel was very small, only really fit for baring. Maneouvering in a tight spot you had to pray to the good Lord that you did not run out of air. If you did, luck was often in short supply Too. Noel

10ba12ba19/01/2021 14:07:23
28 forum posts
14 photos

Watkins, Vol 10, part 1, plate 30 shows at least one gib head key fitted to the inboard end of a flywheel or coupling which incorporates what looks like internal barring gear.

Ramon, you have a PM


Edited By 10ba12ba on 19/01/2021 14:10:02

Edited By 10ba12ba on 19/01/2021 14:22:18

DiogenesII19/01/2021 14:31:43
198 forum posts
88 photos

..and just to complicate matters further, here is another description containing the bolting arrangements to be employed..



..from Henry Spooner's 'Machine Design Construction and Drawing' (Longman's, Green & Co., 1908) included because of it's direct relevance to the specific context of the discussion.

..By the terms 'Two Crank' & 'Three Crank' I surmise he means two- and three-throws - i.e. twins or triples..

Edited By DiogenesII on 19/01/2021 14:36:43

JasonB19/01/2021 14:40:07
19973 forum posts
2179 photos
1 articles

In the end it may well come down to what is going to allow the model to tick over smoothly on air as you will not have a prop and shaft and presumably a thrust box to smooth things out. There is also the lack of expansion from running the compound on air to further complicate things.

Prestons has a few engines over six pages of similar size that may be worth a look through , this Thornycroft on the last page is probably the clearest flange mounted flywheel and also about the largest diameter though it is quite narrow. There are quite a few more engines with more compact ones complete with barring holes.

If all else fails Ramon you could keep the flywheel in place with your favourite JBWelddevil

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