Let's ban Loctite!

A special section just for steam engines and boilers, as without these you may as well fit a sail.
Post Reply
User avatar
malcolmd
Full Steam Ahead
Full Steam Ahead
Posts: 119
Joined: Sun Feb 20, 2011 4:19 pm
Boat Name: Steam Yacht Befur

Let's ban Loctite!

Post by malcolmd » Thu Jan 31, 2019 7:40 pm

In the middle of making a new crank - all because of Bl**dy Loctite!

Discuss....

Read the fully story on the blog !
Last edited by malcolmd on Fri Feb 01, 2019 4:19 pm, edited 1 time in total.
Malcolm Duckett
Mechanical Hacker (Apprentice, age 60+)
Befur's Blog
RGSP
Full Steam Ahead
Full Steam Ahead
Posts: 246
Joined: Mon Dec 14, 2015 2:12 pm
Boat Name: Platypus, Shelduck
Location: Very eastern England

Re: Let's ban Loctite!

Post by RGSP » Fri Feb 01, 2019 10:00 am

I'm inclined to agree with you (and the esteemed Mr Maltby) about not using loctite in complex built-up launch crankshafts. As you say, there are several failures reported in addition to your own.

However....

There are crankshafts around, held together with loctite, which have been in faultless service for decades. Why the difference? I think it's rather complex and difficult to be sure about, but comes down to getting the conditions for the glue exactly right. I've used loctite regularly for (non-critical) assembly of small parts), and usually it works well, but sometimes doesn't. It's a cop-out, but I think it comes down to practice: whenever I've done a moderate batch of parts, all but the first one or two have been perfect (and sometimes the first ones too, but not always). Preparing, applying, and assembling loctited joints is NOT simple, and with something like a crankshaft you're not going to have any practice runs, which comes down to saying don't use it in that application, and if you do use it, the result may not be trustworthy.

Built-up cranks do of course have several things going for them, as well as their snags. Tapers and bolts are good, and given the right tools and jigs can be very good indeed, but the need for bolting adds weight and clumsiness. Accurate parallel turning (or even simple parallel grinding) is something I know I can do if I take enough care, and furthermore 50-ton-or-more hydraulic presses are not expensive as long as you don't want something that will stand up to repeated factory use. But those of us who've dealt with pressed-together motorcycle cranks know that they usually require "truing" using a large mallet after assembly, which I've helped someone else do once or twice, but as said elsewhere in this forum, it makes me cringe. Truing up a complete Leak crank doesn't bear thinking about, though I dare say some brave soul somewhere has done it, or something similar.

The saving grace to all this is the multitude of smallish independent workshops who will grind or regrind crankshafts accurately, and do it cheaply too, so a less-than-perfectly-machined crankshaft from casting or solid billet is entirely viable. Let those who can machine journals on complex cranks well enough to use straight from the home-workshop lathe do so, and I congratulate them, but doubt the capabilities of myself and my machinery are up to it.
User avatar
malcolmd
Full Steam Ahead
Full Steam Ahead
Posts: 119
Joined: Sun Feb 20, 2011 4:19 pm
Boat Name: Steam Yacht Befur

Re: Let's ban Loctite!

Post by malcolmd » Fri Feb 01, 2019 11:52 am

RGSP I agree with everything you have said.
  • Good/appropriate Loctite surface prep is probably more of a science than I can necessarily manage and (as you say) may well point to the problem.
  • "Bumping" motorcycle crankshafts was (as you say) the normal approach (even documented in the manufacturer's workshop manuals) to truing built-up cranks.
  • The process of peeing straight a bent crankshaft is something I have tried successfully (having come across it via racing Small-Block Chevrolet engines), except that it also caused the failure of one of the loctited joints. (That should have been a warning).
  • I have limited experience of pressed joints, but shrunk joins (using heating) I know are very secure, and while it's just a single example, when I shrunk the wheels onto the axles of my 5" loco they never moved - and because one went on twisted I also discovered that it was impossible to "bump" that true (as in the M/C crank example). So, I have come to the conclusion that these type of joint are far more secure than pressed ones.
The net of all this is that I want to make the community aware of the "suspect" nature of using loctite (or other adhesives) in the manufacture of Marine Steam cranks, as I was unaware of the problems, and it cost me a year's happy steaming and quite a lot of time and money (but, as I only tinker for a hobby, quite a lot of interesting work too). This approach has clearly caused problems for a number of builders, and yet seemed to be a hidden secret.
Malcolm Duckett
Mechanical Hacker (Apprentice, age 60+)
Befur's Blog
User avatar
DetroiTug
Full Steam Ahead
Full Steam Ahead
Posts: 1863
Joined: Fri Nov 27, 2009 5:56 pm
Boat Name: Iron Chief
Location: Northwest Detroit

Re: Let's ban Loctite!

Post by DetroiTug » Fri Feb 01, 2019 3:09 pm

Agree with Jack on this, Loctite should never be used for crankshaft assembly.

Loc-tite is a great product when used as intended, thread locker and a bearing seat. It was never intended to be used as an adhesive for structural components. I see these folks on YouTube "gluing" model steam engines together, as a machinist it's really quite appalling and unnecessary. I did not realize, folks we're trying to use it in full size steam engines. Think about the smooth steel impervious surfaces glued together subjected to copious amount of water and creeping oil and the occasional high shock load of the propeller running aground, I'm surprised this has ever worked for anyone.

Sorry yours didn't hold up and that someone gave you some bad advice along the way, Loctite isn't really a glue, it never seems to harden completely and when it cures it just goes to a gummy crumbly state, it's only purpose is to keep bolts from vibrating out and one surface of a bearing from slipping - both very low torque applications.

Press-fit, heat shrink, keyways etc are all much better means of securing components on shafts. With our low power requirements, I just key cranks together then drill in through a shallow spot in the counterweight with a set screw.

-Ron
User avatar
Lopez Mike
Full Steam Ahead
Full Steam Ahead
Posts: 1903
Joined: Wed Dec 07, 2011 6:41 am
Boat Name: S.L. Spiffy
Location: Lopez Island, Washington State, USA

Re: Let's ban Loctite!

Post by Lopez Mike » Fri Feb 01, 2019 6:03 pm

I used to race a three cylinder 750cc two stroke motorcycle with six roller main bearings. Due to extreme stresses it was necessary to take the crank apart regularly to replace the connecting rods and bearings. It produced 110 h.p. (82 kw) at 9000 rpm.

This crank was entirely pressed together. I did it all with a cheap hydraulic press. 10 tons (~9k kG) maximum pressure. The rod and main pins were machined with an interference fit of one part per thousand and I never had a failure of the pressed joints. Any tighter fit than that with steel simply stretched the steel beyond it's elastic limits and when taking it apart the next time I would find that the clearance was back to one part in a thousand.

The process of truing the crank was as previously described in this series of posts. It involved some stout work with a lead hammer and the use of my lathe and a dial indicator to test the progress. I did not hammer on the crank when it was mounted in the lathe! Less than .001" of runout was considered good enough.

To disassemble and reassemble a crank usually took me a long evening.

I tried once to assemble one of these cranks with a special high temperature Locktite that I had to special order including a special priming spray. The manufacturers recommended procedure involved careful measured clearances of two parts per thousand and a post assembly bake at a moderate temperature. I assembled and bonded the crank in it's future home, the engine crankcase. It came out perfectly in line. No measurable runout on the dial indicator.

After the engine was assembled and installed in the motorcycle it ran very smoothly.

Sad to say, it only took a few minutes for the bond to fail. I believe that the failure was due to excessive heat. I had no way to measure the temperature of the crankshaft in service.

My current launch engine, a Strath Steam Warrego, is pressed together. No problems.

One of the advantages of a pressed assembly is that you can often purchase round stock that is very accurately and smoothly ground to dimension for both the crank pins and main shafts. Far nicer than can be done in a home shop.
If you think you are too small to make a difference, try sleeping with a mosquito.
Dalai Lama
RGSP
Full Steam Ahead
Full Steam Ahead
Posts: 246
Joined: Mon Dec 14, 2015 2:12 pm
Boat Name: Platypus, Shelduck
Location: Very eastern England

Re: Let's ban Loctite!

Post by RGSP » Sat Feb 02, 2019 11:49 am

Lopez Mike wrote:
Fri Feb 01, 2019 6:03 pm
This crank was entirely pressed together. I did it all with a cheap hydraulic press. 10 tons (~9k kG) maximum pressure. The rod and main pins were machined with an interference fit of one part per thousand and I never had a failure of the pressed joints. Any tighter fit than that with steel simply stretched the steel beyond it's elastic limits and when taking it apart the next time I would find that the clearance was back to one part in a thousand.

The process of truing the crank was as previously described in this series of posts. It involved some stout work with a lead hammer and the use of my lathe and a dial indicator to test the progress. I did not hammer on the crank when it was mounted in the lathe! Less than .001" of runout was considered good enough.

One of the advantages of a pressed assembly is that you can often purchase round stock that is very accurately and smoothly ground to dimension for both the crank pins and main shafts. Far nicer than can be done in a home shop.
Mike,
you encourage me to get my own workshop press - and use it! I presume the jigging for assembling a 3 cylinder crankshaft (or dis-assembling it) is fairly complex, but feasible, and I'd appreciate a rough description: I'd only want to go to two cylinders max. The presses currently available based on bottle jacks are almost ridiculously cheap, and the only overt snags seem to be lack of a pressure gauge, and no sideways adjustment of the ram. What do you think?

Dick
User avatar
Lopez Mike
Full Steam Ahead
Full Steam Ahead
Posts: 1903
Joined: Wed Dec 07, 2011 6:41 am
Boat Name: S.L. Spiffy
Location: Lopez Island, Washington State, USA

Re: Let's ban Loctite!

Post by Lopez Mike » Sun Feb 03, 2019 4:34 am

As I remember (this was in 1974-5!) the only tricky bit was getting the angles right between the cylinders. In your case, 90 degrees.

My memory is that I pressed the center main shaft into one of the webs to it's full depth. Then I pressed the other web onto that center main shaft just enough that it was lined up as close as I could eyeball to 120 degrees (90 in your case). Then I clamped the assembly in a V block and nudged the partly installed web as close to the correct angle as possible. The jig was fairly simple and as I remember involved rotating the assembly back and forth against two adjustable stops followed by more whacking with the lead hammer. It seems to me that once I got the two webs at the correct angle when they were partially pressed together, they didn't drift much when pressing them all the way together.

Then, in your case, press in a couple of crank pins and then a repeat of the partial pressing, aligning with the jig, and more pressing. Then between centers on the lathe for precision measurements and further brutality.

This all comes under the category of legislation and sausage. Never let the consumer watch the process!

Ah, yes. I just remembered another thing. Once a main shaft was aligned exactly, I crudely drilled about an axial 3/16" hole for a pin that was half way in the shaft and half way in the web. Thus the next time I had the stinking thing apart, the pin aligned things automatically. All that fussing to get the 120 degrees was only on the first crank assembly job. The next time things went much faster. Then only the crank pin to web angles were left to rude methods.

It all sounds much more difficult than it was. You would be surprised how much of a change in angle you can get with one stout blow on a 1" shaft in a 1" hole.

The beauty of this, as I've mentioned. is that your main and rod journal sizes are right before you even start. Just whack off the right lengths of drill rod and add a couple of centers on the main shaft ends. I made my webs from an odd bit of large diameter shaft (4"?). Band sawed off the right number of disks, bored the two holes in each disk and milled away anything else that wasn't needed thus the counterweights were part of the webs. These engines were run at high speeds so the amount of counter balance was important. The fine balance work was done with the drill press. At our low speeds I honestly don't know how important it would be. A subject for another discussion.
If you think you are too small to make a difference, try sleeping with a mosquito.
Dalai Lama
Mike Rometer
Full Steam Ahead
Full Steam Ahead
Posts: 936
Joined: Sat Aug 13, 2011 6:41 pm
Boat Name: B.N.Y.S.
Location: Middle Earth

Re: Let's ban Loctite!

Post by Mike Rometer » Sun Feb 03, 2019 9:56 am

I don't think that even a degree or two (but no more) out of 90 will make a noticeable difference at our low revs. The only likely way to tell would be 'chuff' and that is rarely, truly dead on, anyway. Like L.M. I've done motorcycle engine shafts and it's just a question of good technique and plenty of forethought. The forethought part reduces with experience.

For my twin I will press the crank pins in fully home to the middle webs, first. Then the centre main shaft to one of the middle webs, then press on the second one (checking the angle). The outer mains will be pressed in fully home, then the outer webs pressed to the centre assembly, one at a time. Each stage will be trued for angle and alignment. (I think I've written that correctly, I've re-read it and I understand it!!!) I've a bit to go before I get round to that bit, as I haven't worked out the counter-balance weights yet, or cut them.

Getting back to the O.Ps thoughts, don't Loctite specify a minimum clearance to allow for space for the Loctite crystals to form? i'e. a 'press' fit is too tight anyway. Something like that, in the dim and distant, is floating in my lonely grey-cell.
Retirement is about doing what floats your boat!

A BODGE : - A Bit Of Damn Good Engineering.
User avatar
malcolmd
Full Steam Ahead
Full Steam Ahead
Posts: 119
Joined: Sun Feb 20, 2011 4:19 pm
Boat Name: Steam Yacht Befur

Re: Let's ban Loctite!

Post by malcolmd » Sun Feb 03, 2019 2:41 pm

Mike Rometer wrote:
Sun Feb 03, 2019 9:56 am

Getting back to the O.Ps thoughts, don't Loctite specify a minimum clearance to allow for space for the Loctite crystals to form? i'e. a 'press' fit is too tight anyway. Something like that, in the dim and distant, is floating in my lonely grey-cell.
Yes, they do - and I followed that advice... to no avail! ;)
Malcolm Duckett
Mechanical Hacker (Apprentice, age 60+)
Befur's Blog
Post Reply