Author Topic: Fin repair  (Read 1799 times)

Online Brian

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Fin repair
« on: 02.01. 2016 03:04 »
This is going to be a ongoing "watch this space" type of subject.

Some time ago I was given some A10 parts and amongst it all were these barrels. As you will see by the photo they have been severely butchered. However they are big fin, thick flange and currently on +.020" so have two rebores left in them which I think makes it worth having a go at repairing them.

I dont have any donor fins so intend to use 3mm mild steel plate which I will weld with a mig.

I have repaired quite a few fins in the past on my bikes and others using a mig and so far it has been very successful with no failures (yet!). I have not tackled a job quite this large before though. I have found the trick with welding cast in this situation is not so much what type of welder you use but to keep the heat to a absolute minimum which is where the mig is good as you can "stitch" weld very easily.

I will take photos as I go and report back, for better or worse.

Online KiwiGF

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Re: Fin repair
« Reply #1 on: 02.01. 2016 03:36 »
I'm definitely interested in the technique you use and the results, the cylinder head on my bike has had the top fins modified I guess because at least one side was broken, and it's on the to do list to one day make them look standard again. Either that or find a good cylinder head, but sometimes it's better to work with the devil you know  *bash*

I do have a couple of donor small fin heads but it would be a shame to use them if it's avoidable as some one might need them one day.

As you will be welding from the underside of the fins only (I guess), do you expect to have to deliberately start with the new bits of fin angled up slightly to compensate from the weld shrinking and pulling the fin down when it cools? Or can the weld shrinkage be negated by another technique?



New Zealand

1956 A10 Golden Flash EA7-168x, CA10 913x, left BSA together for Liverpool, 5th Dec 1955.

1949 B31 rigid “400cc hot rod” (favourite bike)

1949 C11 rigid, but why!!! (cos it was cheap)

1937 B21, missing parts so mission impossible?

1952 Armstrong Siddeley Whitley for rainy days (with wife).

GL1800 Goldwing not sure why, maybe cos it always starts

Online Brian

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Re: Fin repair
« Reply #2 on: 02.01. 2016 04:07 »
Here's one I prepared earlier !

The same barrels had a small piece missing at the top which I have already repaired using a bit of mild steel plate.

I will be welding them from the underside only and getting the angle right will be a bit tricky as with the distance from the weld to the outer edge of the fin is so far a small amount of "pull" at the weld will make a big difference at the outer edge. Once I have welded one fin I will have a better idea of how much it is going to distort.

Even if I do end up with the fins not perfectly level once it is painted and on a bike it shouldnt look too bad.

The whole process is really about trying to save a set of barrels that otherwise would be scrapped.

Online orabanda

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Re: Fin repair
« Reply #3 on: 02.01. 2016 07:43 »
Brian,
Well done; you have achieved a good FINish!

Richard

Online Klaus

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Re: Fin repair
« Reply #4 on: 02.01. 2016 08:45 »
l have repaired some lost  fins also with mild steel.
But l only fixing the rebuild fins with two MIG weld points.

The breakline was V angled and then l have give them a  braze welding.

So we had a solid contact to conduct away heat.

hard job to do Brian, good luck *good3*

cheers Klaus


If you think, everything is under control, you are not fast enought.

Offline terryg

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Re: Fin repair
« Reply #5 on: 02.01. 2016 10:47 »
Following with interest.

Have both a kick-start quadrant and inner gearbox case awaiting the courage to start welding.

Getting a lot of practice on a VW Beetle at the moment. All steel though.
Terry
'57 'SR', '59 SR, '63 RGS

Offline nimrod650

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Re: Fin repair
« Reply #6 on: 02.01. 2016 16:29 »
Here's one I prepared earlier !

The same barrels had a small piece missing at the top which I have already repaired using a bit of mild steel plate.

I will be welding them from the underside only and getting the angle right will be a bit tricky as with the distance from the weld to the outer edge of the fin is so far a small amount of "pull" at the weld will make a big difference at the outer edge. Once I have welded one fin I will have a better idea of how much it is going to distort.

Even if I do end up with the fins not perfectly level once it is painted and on a bike it shouldnt look too bad.

The whole process is really about trying to save a set of barrels that otherwise would be scrapped.
done a few same method i place a piece plywood  right thickness between fins and clamp repair piece to it weld an allow to cool

Online Greybeard

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Re: Fin repair
« Reply #7 on: 02.01. 2016 17:06 »
Do you know if those fins been removed for a reason?

Offline nimrod650

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Re: Fin repair
« Reply #8 on: 02.01. 2016 21:21 »
Do you know if those fins been removed for a reason?
have they been modified to run on methanol  they used to remove fins because they run so cold

Online Brian

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Re: Fin repair
« Reply #9 on: 02.01. 2016 21:26 »
No, I have no idea why these were butchered.

A couple of years ago I was given a heap of A10 parts but it was all like this, everything had been cut, chopped or generally mangled. Most of it was beyond any sort of repair but I did manage to salvage a few bits, these barrels being one of them. I also got a big journal crank that still has one grind left in it.

You have to remember that in the late 60's and 70's this sort of stuff was junk, nobody wanted it and truck loads of good motorcycle parts got taken to the scrap metal dealers. We look at something like these barrels and think "why on earth would you do that" but back then it was junk so to smash a few fins off a set of barrels was of no concern.

That is also the reason I want to salvage these barrels if I can, currently if you need barrels you can search the internet or dealers and find some but in 50 years time who knows so if it is at all possible to save them for future use I would like to.

Online trevinoz

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Re: Fin repair
« Reply #10 on: 02.01. 2016 21:34 »
While we are on the subject of barrels, recently I was given a set of the very late type, the ones with the staggered front fins.
However, while every fin is intact and they are only about .020' over, they have had a massive blow up and they are cracked above the flange right through the cam follower tunnel.
Irreparable but sitting as a donor for the future.

Online Brian

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Re: Fin repair
« Reply #11 on: 02.01. 2016 21:44 »
It does concern me a little that maybe we still throw away parts that may one day be repairable.

Cranks are probably a good example. There has been much discussion about building cranks up with spray metal etc etc and maybe now it is not entirely successful but in 50 years time with advances in technology it may well be quite easily done.

We all have to remember there will be generations after us that will want to ride our bikes and will need parts so dont throw away anything without having a very close look first.

Online trevinoz

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Re: Fin repair
« Reply #12 on: 02.01. 2016 22:03 »
A friend of mine tossed a heap of SJ cranks into the bin as nobody wanted them and he didn't have space to keep them.

Online Brian

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Re: Fin repair
« Reply #13 on: 02.01. 2016 22:14 »
I wonder if anyone has ever had a large journal crank ground down to small journal size. It would have to be re-hardened of course but nitriding is not that expensive.

It might be seen as a backward step but could get engines on the road if parts ever get that hard to find, just a thought.


Online KiwiGF

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Re: Fin repair
« Reply #14 on: 02.01. 2016 23:03 »
For small journal cranks I've heard triumph con rods can be used that allow one to go beyond -040, the SJ cranks have a relatively small sludge trap hole through the big end journals .... so would still have quite of strength left if this was true.

A better solution (for me) would be one where I could keep my nice (BSA) billet alloy con rods though  *doh*
New Zealand

1956 A10 Golden Flash EA7-168x, CA10 913x, left BSA together for Liverpool, 5th Dec 1955.

1949 B31 rigid “400cc hot rod” (favourite bike)

1949 C11 rigid, but why!!! (cos it was cheap)

1937 B21, missing parts so mission impossible?

1952 Armstrong Siddeley Whitley for rainy days (with wife).

GL1800 Goldwing not sure why, maybe cos it always starts