Pinning a crankshaft.

[Mark P.Participant @markp]

Hi all, what is the best thing to pin a built up crankshaft,eg silver steel pins, steel pins (nails) or taper pins?
Also does anyone have anything on the history of the Suffolk dredging tractor, like what company built it etc.

Mark P.

[Mark P.Participant @markp]

[Dougie SwanParticipant @dougieswan43463]

I use roll pins and sink them a little lower than the surface and fill with car body filler if it is to be painted or silver steel filed flush if it is left bright

Dougie

[duncan webster 1Participant @duncanwebster1]

If you're using loctite then I don't see why you'd want to pin it. The loctite is VERY strong, I once broke a 1te jack trying to get some 5"g wheels off. It is arguable that pinning weakens the assembly as it causes stress raisers.

[martin perman 1Participant @martinperman1]

Mark P,

This link http://www.stationroadsteam.co.uk/stock%20pages/2240/index.htm shows a Garrett Suffolk tractor and at Leiston Longshop there lives a full size one.

Martin P

[Michael GilliganParticipant @michaelgilligan61133]

Posted by duncan webster on 02/07/2016 13:02:07:

If you're using loctite then I don't see why you'd want to pin it. …

It is arguable that pinning weakens the assembly as it causes stress raisers.

.

+1

MichaelG.

[JasonBModerator @jasonb]

I just use mild steel to pin mine as once filed flush it becomes invisible, seldom use loctite for built up cranks as the IC engines have far more of a kick to them than steam.

These are just 1/8" BMS pins, peined over into shallow CSk holes.

[Brian HParticipant @brianh50089]

I once used Loctite to build a loco crankshaft and it moved whilst setting. I had to heat it to a dull red before it reluctantly came apart. That convinced me how good the product was.

It is important to choose the correct grade and to clean everything thoroughly before assembly. The joint can be moved to correct any errors but only for a short time.

[Mark P.Participant @markp]

Thanks for the replies,food for thought there. Jason when you cut through the “main shaft” do you hacksaw and file it,or stick it in the miller and machine through it?

Mark P.

[JasonBModerator @jasonb]

Hacksaw and file for me, make sure the pin is below the level of the vice jaws so you don't nick it with teh saw as it breaks through. Nice fine file with some chalk rubbed into it to finish.

[Roderick JenkinsParticipant @roderickjenkins93242]

My Wyvern crankshaft is Loctite only. It's lasted so far but I guess only time will tell.

HTH

Rod

[Mark P.Participant @markp]

Thanks Jason, that’s what I will do.
Mark P.

[GwilParticipant @gwil]

A question for Jason – you say "I just use mild steel to pin mine…" but the photos seem to show something filling the joints, although I can't tell what it is. Could you clarify please? Thanks.

[JasonBModerator @jasonb]

The main joints in that one were silver soldered and then I drilled & pinned for good measure. Due to the soldering method you can't be sure how far through the joint the solder has wicked.

Full description of that crank's construction here

[GwilParticipant @gwil]

Very interesting. Thanks for the link.

[Nigel McBurney 1Participant @nigelmcburney1]

Taper pinning makes a far better job ,they really make a firm joint.

[duncan webster 1Participant @duncanwebster1]

Silver soldered then drilled and pinned! You must have little confidence in your silver soldering. As the silver solder joint is a lot stiffer than a cross pin you won't get significant load sharing, the pin does nothing apart from cause a stress raiser until the silver solder gives up (which it won't), but then it's too late.

[JasonBModerator @jasonb]

Posted by duncan webster on 04/07/2016 17:51:19:

You must have little confidence in your silver soldering.

Exactly.

Had this been your usual silver soldered joint I would have been looking on the opposite side of the joint to where the rod was applied for a small fillet of solder which would indicate that I had got good penitration of the joint.

I don't know if you went to the link I posted but if you did you must have missed that the idea with this method is not to let the solder penitrate the whole joint and come out the other side so that the bearing surfaces remain free of solder and required little clean up. So unless I saw through the joint there is no easy way to know if I just have the CSK filled with solder, or Csk plus 10% of the joint or Csk plus 95% of the joint.

So given that the joint won't be full penitration I followed the drawings and also pinned the joints. Also I don't know about you but I have not been able to get silver solder to penitrate a press fitted joint as spec'd on the drawing.

This is a popular engine and many have been made in various scales over a long period of time, I've never heard on one of the cranks failing due to stress risers from the holes. I have also used this method since on several other built up cranks and all are running fine.

J

[julian atkinsParticipant @julianatkins58923]

I think the criticism of Jason's use of pins is a totally misplaced. It is a very sensible pragmatic approach and ensures that in the event of a joint failing the assembly remains secure without causing damage.

I would never use roll pins, and taper pins are unnecessary as they will never have to be removed, so solid parallel pins are quite ok.

In Jason's drawing above, I would loctite everything rather than silver solder, and I would dispense with the stepped journal.

Cheers,

Julian

[duncan webster 1Participant @duncanwebster1]

I must admit it never occured to me that anyone would attempt to silver soder a press fitted joint.

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by julian atkins on 04/07/2016 22:32:07:

I think the criticism of Jason's use of pins is a totally misplaced. It is a very sensible pragmatic approach and ensures that in the event of a joint failing the assembly remains secure without causing damage.

Oh ye of little faith!

In Jason's example the glue or silver solder is only really being used as an assembly aid. I was going to use taper pins on my crankshaft but was having difficulty finding metric pins to match the one taper (3mm) reamer I have. I then took the view that as I'd made it I could repair it in the event of failure so carried on without the pins – it's an experiment . I think the problem is that we have very little data on the longevity of joints made with organic retainers in our particular model engineering situations although they are extensively used in industry. Perhaps over time we will develop more confidence. Otherwise, belt and braces never hurt.

Rod

[JasonBModerator @jasonb]

The other thing is we don't know any details of Marks Crank, it could be for a wobbler or a 6" traction engine. While I would happily suggest loctite for one of those I would not for the other. The question was what to pin with so that is the question I answered.

As an example you can just see Rod's small blue wyvern next to my somewhat larger Galloway which the crank I have shown above is for. There is also the fact the Wyvern is throttle goverend so fires every cycle whereas the Galloway may onlt fire every 5-7 cycles with quite a kick that has to accelerate the two 10.5" flywheels back upto speed.

As they say there is more than one way to skin a cat but it helps to know the breed first.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 05/07/2016 07:28:04:

The other thing is we don't know any details of Marks Crank, it could be for a wobbler or a 6" traction engine. While I would happily suggest loctite for one of those I would not for the other. The question was what to pin with so that is the question I answered.

As an example you can just see Rod's small blue wyvern next to my somewhat larger Galloway which the crank I have shown above is for. There is also the fact the Wyvern is throttle goverend so fires every cycle whereas the Galloway may onlt fire every 5-7 cycles with quite a kick that has to accelerate the two 10.5" flywheels back upto speed.

As they say there is more than one way to skin a cat but it helps to know the breed first.

.

Very fair observations, Jason … But forgive me if I question your logic:

In an earlier post, you wrote; "I … seldom use loctite for built up cranks as the IC engines have far more of a kick to them than steam." and here you confirm that "Galloway may onlt fire every 5-7 cycles with quite a kick that has to accelerate the two 10.5" flywheels back upto speed." … So your reasoning is fairly obvious.

Strangely, however, your conclusion is exactly the opposite to what mine would have been

Using the same 'inputs', I would have concluded that a 'bond' which is fully distributed over the joint area would be more resistant to the kick, and would therefore have used either a fully silver soldered joint, or [more likely] Loctite 638.

I fully accept that what you have done works well for you … I simply offer that thought for discussion.

MichaelG.

[Martin KyteParticipant @martinkyte99762]

Just an observation that so far, unless I missed something, everyone has described methodology that has worked which tends to indicate all methods are sound. What would be more instructive would be any information on failures on the basis that it's useful to know what you have to do better than. I guess it's the old 'you learn more from your mistakes than your successes.

regards Martin

[Mark P.Participant @markp]

Hi There, should have said my crank is a double throw for my 3″Suffolk dredging tractor. I have now loctited and pinned it with mild steel pins.
Mark P.

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