Author Topic: 2 HP Big End Bearings  (Read 9228 times)

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Offline RobertC

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2 HP Big End Bearings
« on: 07 Dec 2009 at 11:51 »
I am in the process of rebuilding the motor on my 2 hp machine and am unclear about how to tackle the big end bearings. There is some wear at present and I need to try and improve the fit between the bearings and crank journal. As far as I can tell, the bearing is a split bronze insert that runs directly on the journal I cannot see any evidence of white metal. How can the bearing be resized to improve the fit on the journal, or should I send it away to have it white-metalled to suit?

Thanks for any help.

Robert

Offline ian scott

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Re: 2 HP Big End Bearings
« Reply #1 on: 08 Dec 2009 at 10:43 »
Hi Robert,

The bearings are not white metalled but simply split bronze bearings. They have steel spacers in the split which protrude from the gap where the conrod cap meets the rod. These prevent the bearing from spinning in the rod.

Here is how you remake them-

1. Choose some material, the same thickness as your original spacers (to make new spacers) but get a fair bit more than what you will need than just for the spacers.

2. Have enough of the bronze material for your bushes (plus extra to hold in a lathe chuck) split along its length.

3. Cut two strips of your spacer material the same length as your bronze about 1/8" wide.

4. Tin the split surfaces of your bronze and both sides of the 1/8" wide steel strips with soft solder.

5. Put the two tinned bronze halves back together with the tinned 1/8" steel strips in the split- spaced about the centre, at roughly the diameter of the bush and hold firmly in a vice.

6. Warm the bronze till the solder you applied melts. Keep some pressure on the vice handle. Allow to cool.

7. Turn your soldered up bronze on a lathe to make your new bearing. The outside diameter size for size with the big end size of your conrod. I have given my inside diameter 0.001" clearance on the crank. Face and part off to width.

8. Warm up till the bronze and steel fall apart and you have the two halves of a new bearing. Discard the pieces of steel.

9. You can assemble the new bearings with new spacers or reuse the old ones if they are serviceable.

Good luck. If you're not handy with a lathe I'm sure you will find a capable machinist in your area to do the work for you.

Offline Chris

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Re: 2 HP Big End Bearings
« Reply #2 on: 08 Dec 2009 at 15:44 »
Hi Robert
    Ian's suggestion is one way of doing it there are others but as you say there is some wear to start with it is important that you get the journals right to start with or the bronze shells will never fit properly. Invariably you will find that the journals of the crankshaft  are worn not only oval but tapered. It should be possible to get the crankshaft reground but you will have a job finding someone to do it as these journals are much narrower than anything found in the automotive field. Engine re-conditioners are not prepared to slim a very expensive large diameter crankshaft grinding wheel down to the required thickness just to suit the occasional early vintage Douglas owner. I have made the journals parallel and round by simply filing them with regular uses of a micrometerand using finer and finer emery cloth to finish them. I have heard of others making up a lap to fit the journals and putting the shaft in a lathe letting the lap work on the journal until it is round and parallel. Don't make the shells too tight a fit, there has to be room for the oil.   Chris.

Offline Edin

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Re: 2 HP Big End Bearings
« Reply #3 on: 08 Dec 2009 at 18:24 »
Hej Robert
Just a little inspiration to make repair of your crankshaft. The job can be done on  a small lathe with a support grinder.
Be patient and carefull with finding the center before start grinding.
It is much more easy than you think.
Enclosed fotoserie shows how to do it.
Good luck - regards Edin DK











« Last Edit: 08 Dec 2009 at 19:07 by Dave »

Offline Dave

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Re: 2 HP Big End Bearings
« Reply #4 on: 08 Dec 2009 at 19:07 »
Photos added.

Offline ian scott

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Re: 2 HP Big End Bearings
« Reply #5 on: 09 Dec 2009 at 10:16 »
Invariably you will find that the journals of the crankshaft  are worn not only oval but tapered...        ....I have made the journals parallel and round by simply filing them with regular uses of a micrometer and using finer and finer emery cloth to finish them...     ....Don't make the shells too tight a fit, there has to be room for the oil.   Chris.

Yes sorry to omit this as I was focusing on the bearings. I trued up my big ends in the same manner that Chris suggests. Be patient here as this takes a bit of time. The crank is not hard so a file and emery are adequate.

Good luck.

Offline eddie

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Re: 2 HP Big End Bearings
« Reply #6 on: 09 Dec 2009 at 12:17 »
Robert,
             The method I prefer to adopt when reconditioning 2 bigends is, first, to check out the bigend eye of the conrod. The mating faces of the rod and cap should be truly flat, and then, with .062" spacers fitted (in lieu of the keep plates), the eye should be truly round. If not, then it may be necessary to set the rod up in the lathe and take a light skim out of the eye. Take a note of the bore size - the new bronze 'shells' will need to be this diameter or a couple of thou larger. Having turned up a bronze bush to suit the bore of the conrod and with a bore 2 thou larger than the crankpin, fit the bush into the conrod and with a sharp scriber, mark the position of the ends of the 'shell'. Cut the bush in half with a junior hacksaw, just clear of the lines and then machine up the ends so that it fits the rod and stands a couple of thou proud of the joint face. Fit the remaining half of the bush into the conrod cap and repeat the procedure. This way, the joint in the shells is in line with the joint of the conrod and cap - if you adopt the method of soldering the 2 halves to the spacers and then finish machine it, there is no guarantee that the joint will align with the end of the rod - with the result that one or both of the shells will not be clamped in by the keep plates.
       With the rod and shells reassembled with new keep plates, the whole should be a free fit on the crankpin - remember, there is no pressure fed oiling on these engines, so there has to be enough clearance for oil to find it's way into the bearing. Also, with poor lubrication, heat will be generated inside the shell, which, on cooling, will curl tighter and be a permanent tight fit on the journal (as well as slack in the rod).
       If the assembled conrod/bigend is too tight on the crankpin, dismantle and scrape away any high spots - do not resort to emery cloth - this will only leave small particles of grit embedded in the bronze, causing further subsequent damage to the crankpin. If in doubt, err on the side of a couple of thou slack in the bearing, rather than tight. These engines run much more happily when they are free to rev.
                             Regards,
                                       Eddie.

Offline RobertC

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Re: 2 HP Big End Bearings
« Reply #7 on: 09 Dec 2009 at 12:24 »
Thanks for the very helpful responses.

Looks like I am going to be very busy over the Christmas break!

Robert

Offline LATDOUGNUT

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Re: 2 HP Big End Bearings
« Reply #8 on: 11 Dec 2009 at 22:26 »
Robert,

May I add to this discussion that it is very important what bronze you will be using. Not just any type or any piece of phosphor bronze will do. From my experience COLPHOS 90 as distributed by Columbia Metals in the UK is "your ticket to Brighton" if you enter the Pioneer Run with your machine -- for the simple reason that this particular type of bronze is made with small lead particles dispersed in it and they act as a lubricant in case of oil shortage.

If you choose some other tough phosphor bronze the chances are that during possible oil starvation the bronze will snap on the shaft and will seize with resulting "bird singing" -- I know too well as I have had it on a veteran machine that had had an engine rebuilt by others...

Lesson No 1: "For the choice of bronze
always use a known brand, not just any piece that looks good enough!"

Good luck!

LATDOUGNUT
No Rest - No Rust. No Trust - No Bust!

Offline RobertC

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Re: 2 HP Big End Bearings
« Reply #9 on: 24 Mar 2010 at 12:58 »
Hi

The crank is now sorted and I am about to machine the bronze bearings. Before I go too far, can I confirm the clearance between the bearing and  the crank journal? If I have interpreted the reponses correctly we are talking about 1 or 2 thou which should be sufficient to enable the oil to do its job.

Thanks again for all the helpful responses.

Robert

Offline LATDOUGNUT

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Re: 2 HP Big End Bearings
« Reply #10 on: 24 Mar 2010 at 17:50 »
Robert,

I am reconditioning 2 very old Pierce engines, the older of the two is splash lubrication, the younger has an oil pump, so pressure lubrication. The diamatre of the crankshafts is close to Douglas cranks. I am using Colphos 90 and the splash lubrication engine will be done with 0.06 mm running clearances, the pressure lubricated one with 0.04 mm clearances. So in your case 1 thou is too tight I think. 2 thou plus a little more is more likely if the crank is square etc. Try to get PLASTIGAUGE for measuring running clearance and do not use it under the cap, but against the main part of the rod.

Good luck with your rods!

Juris
No Rest - No Rust. No Trust - No Bust!