Author Topic: conrods  (Read 1132 times)

Online morris

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conrods
« on: 08.08. 2014 23:28 »
Just a question for my peace of mind, but as I got the barrels and pistons off from the plunger I noticed that when holding the conrods by the top I can move (tilt) them from left to right by about 5 mm. Is this normal?
I can't feel any up and down play so the big end bearings still seem to be ok.
Thanks
'58 BSA A 10 SA
'52 BSA A 10 Plunger
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Online muskrat

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Re: conrods
« Reply #1 on: 10.08. 2014 09:49 »
Sounds about right to me.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Online morris

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Re: conrods
« Reply #2 on: 10.08. 2014 21:54 »
Thanks Musky, that'll make me sleep better tonight *smile*
'58 BSA A 10 SA
'52 BSA A 10 Plunger
'55 MORRIS ISIS
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Online RichardL

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Re: conrods
« Reply #3 on: 11.08. 2014 06:55 »
Morris,

I'm not about to debate with Muskrat about anything, but I did a drawing representing your rod wobble condition and it makes me wonder about whether it's OK.Based on 5mm (total) of back and forth movement, my graphic seemed to say it takes .010" bearing clearance to move 2.5 mm to one side. If my evaluation is wrong, it would be off by 50%, which would mean 0.005 bearing clearance. Still too much, I believe. Some time ago I posted videos of my rod wobble issue. Here is the first one: https://www.youtube.com/watch?v=5IYligiWUac  and here is the correction (the one in the middle is just wrong): https://www.youtube.com/watch?v=G1FSruempm4 . If I am waaaay off base with my graphic arithmetic, I apologize and welcome correction from the throngs here more knowing than I.

Richard L.
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Online Triton Thrasher

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Re: conrods
« Reply #4 on: 11.08. 2014 09:38 »
If Morris had 5 thou up and down clearance, I think he would feel it.

He would also have heard it last time the engine was running.

Online RichardL

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Re: conrods
« Reply #5 on: 11.08. 2014 12:26 »
So, let me put the drawing up for comment. A variety of things might be in question: where I chose to pivot; what the apparent gap means; was "5 mm" wobble measured or approximated?; etc.
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Online muskrat

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Re: conrods
« Reply #6 on: 11.08. 2014 21:19 »
Nice work Richard, but. Mathematics can confuse the truth. I've seen a lot worse (10mm) last another 30Kmiles before it made a racket. I'd be happy to go with morris's rods. (that sounds kinky)
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Online morris

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Re: conrods
« Reply #7 on: 11.08. 2014 22:24 »
Bloody hell Richard, you frightened the hell out of me... *eek*
For correctness, I've measured the wobble. Got 3mm right and 3.5 left so seems to be less worse than first thought.
Strange how the eye can sometimes cheat on you. It really looked like 5mm of movement.
Also checked the up/down play again. There is none in whatever crank position.
Started working on the bike right after I bought it, just ran it up and down the drive a couple of times before dismantling. Can't remember to have heard any knock. In fact, found it was running sweeter than the SA.
Thanks anyway for the drawing.
'58 BSA A 10 SA
'52 BSA A 10 Plunger
'55 MORRIS ISIS
The world looks better from a motorbike
Belgium

Online RichardL

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Re: conrods
« Reply #8 on: 07.09. 2014 21:11 »
I'm in the process of disassembling my '57 A7 and thought some here might find this youtube link interesting. It shows the rod wobble with a metric rule for reference. Also, the photo shows the spun bearing. The crank is on its firts regrind, so I think I got lucky.

1957 BSA A7 Rod Wobble: http://youtu.be/sUa0BDLN7XM

Richard L.
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Online muskrat

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Re: conrods
« Reply #9 on: 07.09. 2014 21:33 »
Nice work Richard. It's very hard to get a good wobble reading when there's end float as well. I see you tried to move the rod without sideways movement.  Try it with a few feeler gauges on each side of the cap, not to make it tight (say 20 thou in a 22 thou gap). I know this would be impossible with the crank in the cases.
I would have expected to see the tangs of the slippers squashed down a bit for them to spin in the rod. Have you put them back in the rod and torqued it up to measure the big end and crank too see how much slop it had?
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Online RichardL

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Re: conrods
« Reply #10 on: 08.09. 2014 03:51 »
I'll put it back together and torque it with plastigage in place. I now realize that the shells must have just stayed in place as I was working the cap off the rod, since an extent of rotating around the pin was necessary after the cap was loose. The pin isn't badly scored and measures 1.444" OD., which I take to be about 0.005 too small after first grind.

Richard L.
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Online muskrat

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Re: conrods
« Reply #11 on: 08.09. 2014 12:55 »
Next grind is 1.440" = -20.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7