Author Topic: slightly distorted  (Read 1176 times)

Offline edboy

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slightly distorted
« on: 27.06. 2015 20:25 »
i thought i would share this with everyone as it surprised me. i ve been rebuilding the bottom end of a plunger a10 and after every stage of assembly checking the crank spins freely. i bolted the inner and outer covers tight to the cases and the crank locked. i wasted most of the day checking for a excessively long case bolt touching the crank.i ve tried other cases with all the same result as they all seem to bow slightly in above the oil pump section. i think i may have to flycut to surfaces on a mill or possibly try a press to flatten them. not sure yet, but anyone else come across this problem?
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Online RichardL

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Re: slightly distorted
« Reply #1 on: 27.06. 2015 20:40 »
Did you fit a new timing-side bush and was it properly line bored and honed? Are your crank shims too thick?
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Online bsa-bill

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Re: slightly distorted
« Reply #2 on: 27.06. 2015 20:41 »
Yes , same thing spun free until the final turn on the case  studs/nuts, took it back to the shop with another bush for them to ream to size and line bore,  fixed and they didn't charge.
presuming the bush had been off square by a small amount but enough to lock it when tightened.
Another cause I checked out and found not to be at fault were to long bigend bolt nuts, but apparently they can   
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1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online orabanda

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Re: slightly distorted
« Reply #3 on: 28.06. 2015 00:08 »
I suspect the timing bush bore has not been machined / reamed at 90 degrees to the mounting surface (bore) of the bearing in drive side housing.

This has to be very accurate. There is something like 10" distance between the drive side bearing, and the timing bush. and the timing bush is being machined to 0.0015"clearance, so if the roller bearing - timing bush bore are not at exactly 90 degrees to each other, I would expect the crankshaft not to turn freely.

If the machine shop seem confused, or want to debate this, or want to attack the timing bush with a reamer, take the job to someone else.

Do not use the press!

Richard
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Offline bikerboy

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Re: slightly distorted
« Reply #4 on: 28.06. 2015 00:55 »
You say you have tried other cases? Have you been swapping the main bush from case to case? If you have that will somewhat make a mockery of the line boring
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Offline duTch

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Re: slightly distorted
« Reply #5 on: 28.06. 2015 09:59 »

 
Quote
You say you have tried other cases?....

 I must be going blind...can't see that anywhere in this thread..??
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Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline edboy

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Re: slightly distorted
« Reply #6 on: 28.06. 2015 10:18 »
interesting replies. i dont believe its the bush which i line reamed anyway. yes , i have other timing cases which all seem to bow slightly from the middle outwards. it doesnt help that i m building an engine from a collection of parts and i will concentrate on the timing covers. it may be the bush or bearing housing at fault and i ve been wrong plenty of times in the past.
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Online bsa-bill

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Re: slightly distorted
« Reply #7 on: 28.06. 2015 11:26 »
I'm a little confused Ed, are you talking about the timing cases being bowed or the crankcases. yes I have timing cases that are bowed but they flatten out when screwed up, can't see the long studs for the timing case having any affect on the crank.
Long case bolts -  the front three primary case bolts (the thicker ones) can be a bit to long and rub on the crank web when it comes around.
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1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline duTch

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Re: slightly distorted
« Reply #8 on: 28.06. 2015 11:53 »
Quote
Quote....You say you have tried other cases?
              ....I must be going blind...can't see that anywhere in this thread..??
Modify message

 I think I just confirmed I'm going blind..... *conf*
Quote
yes I have timing cases that are bowed but they flatten out when screwed up,

 That's good to know, I messed around with mine and they're still the same  *work*
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Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Online RichardL

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Re: slightly distorted
« Reply #9 on: 28.06. 2015 14:16 »
I have never done it myself, but I am rather sure that line reaming (or boring, or honing) is done with the cases bolted together, so, if the cases were indeed warped, it would have been clamped-out during the process. Richard (orabanda) posted some interesting pictures and thoughts on this a while back (http://www.a7a10.net/forum/index.php?topic=3003.msg20855#msg20855).

If the line reaming is indeed correct, it seems to leave a possible bent crankshaft or not enough width in the cases for the crankshaft. If you have solid a phosphor-bronze or home-made bushing, it's possible that the shoulder is too tall.

Richard L.
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Online bsa-bill

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Re: slightly distorted
« Reply #10 on: 28.06. 2015 14:28 »
Quote
it's possible that the shoulder is too tall.

Which should not be the case if shimmed properly, however the cases nipping up makes accurate shimming impossible, it's a bit of a merry go round
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1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online RichardL

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Re: slightly distorted
« Reply #11 on: 28.06. 2015 16:03 »
Bill,

I may be wrong about this, but I think some solid bronze bushes have been made with tall shoulders with the intention of eliminating the shim stack or reducing its height through machining-down the shoulder. I had this done with the last one I had, leaving enough space for what I thought put the shim stack in the right height range while leaving the crank basically centered.

Richard L.
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Offline edboy

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Re: slightly distorted
« Reply #12 on: 28.06. 2015 21:11 »
i better be more clear about this. i ve line reamed the bush to the d/s bearing with a thimble on the end of the line reamer with the crankcases bolted together. the crank was nice and free spinning with the oil pump on. only when i tighten up the outer timing cover screws especially those on the mag and dynamo edges does the crank start to lock up. timing cases are miss and match so thats why i will turn my attention to these first. the main reason i thought i would post this one is because  when we rebuilt the a10  engines 35 years ago we [me and my peers] would chuck them together armed with the haynes manual and ignorance. no wonder we had 2,000 mile rebuilds and oil leaks everwhere. but everyone used to know someone else with a spare engine under a bench so replacements were cheap.
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Online Greybeard

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Re: slightly distorted
« Reply #13 on: 28.06. 2015 21:22 »
What about using Engineers Blue to see the rubbing point(s). I had to use that stuff to scrape in the big ends on my Austin Seven engine. No shells back then; the white metal gets cast onto the con-rod big end halves and high spots have to be carefully removed with a curved scraper tool. Frequent application of Engineers Blue allows the engineer to see where the tight spots are.
https://en.wikipedia.org/wiki/Engineer%27s_blue
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Online bsa-bill

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Re: slightly distorted
« Reply #14 on: 28.06. 2015 22:10 »
Quote
only when i tighten up the outer timing cover screws especially those on the mag and dynamo edges does the crank start to lock up

Whoa - that's the bit I've been missing, puts a whole new twist to it, can't see the timing case warp causing it as it should/would in my limited experience pull to the shape of the crankcase plus inner timing case rather than the other way round.
Wonder if you've got a stranger in amongst the outer timing case studs although off the top of my head I'm unsure if any of them protrude into the crankcase

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All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco