Author Topic: Large journal con-rod dimensions  (Read 529 times)

Offline Clive54bsa

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Large journal con-rod dimensions
« on: 15.10. 2018 00:55 »
Hi does any one out there know what the dimension of the con-rod hole ( where the big-end bearing goes) for a large journal con-rod is supposed to be, after a premature big-end failure on the timing side rod (SRM converion done), I think it may be slightly oval.


'54 GF,  '61 SR

Offline duTch

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Re: Large journal con-rod dimensions
« Reply #1 on: 15.10. 2018 01:29 »

 I have it noted somewhere, can maybe find it later.

  Have a look here; https://www.a7a10.net/forum/index.php?topic=1475.0
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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Online KiwiGF

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Re: Large journal con-rod dimensions
« Reply #2 on: 15.10. 2018 08:21 »
Hi does any one out there know what the dimension of the con-rod hole ( where the big-end bearing goes) for a large journal con-rod is supposed to be, after a premature big-end failure on the timing side rod (SRM converion done), I think it may be slightly oval.

In my limited experience, the con rods are made so accurately you need special equipment to measure them. There is a standard process called “resizing” that is used to get con rods in spec. A small amount is machined off the rods mating surface first.

A motor run with big ends gone will often ”oval” the rod.

See this for a typical vid from the net

https://m.youtube.com/watch?v=e4h49GFKTEU
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1956 A10 Golden Flash (1st finished project)
1949 B31 rigid “400cc” (2nd finished project)
1968 B44 Victor Special (3rd project,in progress)
2001 GL1800 Goldwing, well, the wife likes it
2007 KTM 950 Adventure, cos it’s 100% nuts

Offline Swarfcut

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Re: Large journal con-rod dimensions
« Reply #3 on: 15.10. 2018 08:55 »
  Hi Clive.. Big Journal Conrod Eye Dimensions, Published in my 1987 Glacier Bearing Catalogue

    Standard crank journal  1.6865/1.6870"..........42.837/42.850 mm

    Big End Eye                  1.8435/1.8440"...........46.825/46.838  mm

    Bearing Shell thickness     0.078"....1.98mm


    Bearing shell width     0.705".......17.91mm

   Glacier are now owned by someone else, but if you can find new old stock  the catalogue numbers are   

            B2033LC      Steel Shells, copper-lead lined, with lead-tin overlay

            B2046M        Steel Shells, White metal Lined. 

           They used to be available in 10, 20,30, 40 thou undersizes.  The two variants are interchangeable, the only difference being the bearing material.

   Checking the rods is simple with a suitable measuring. If ovality is present. engine reconditioners can reclaim the rod by removing material from the mating surfaces, reassembling cap and rod, then reboring the eye back to original size.

   Have a look at the Glyco Bearing Website, lots of interesting stuff about bearing materials and crank grinding.

  Keep Spannering,   Swarfy.

Offline duTch

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Re: Large journal con-rod dimensions
« Reply #4 on: 15.10. 2018 09:18 »

 Good thing ^^^...the only measurements I can easily find are what they were measured at by the guy who did the grinding ; Vertical  1.8930/1.8920   Diagonal  1.8926/1.8928  (Left/Right), but I knew they are wrong even before I dug 'em out because I've written over the 9's with 4's *eek* (1.8430/1.8420 & 1.8426/1.8928 )....

 
Quote
.....If ovality is present. engine reconditioners can reclaim the rod by removing material from the mating surfaces, reassembling cap and rod, then reboring the eye back to original size....

 That's good and well if you say it fast...and have someone you can trust- I vaguely recall having mine done long ago but whoever did it put the caps on wrong and just don't fit right...at that point I bit hard and ordered the Thunder rods
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

Offline Swarfcut

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Re: Large journal con-rod dimensions
« Reply #5 on: 15.10. 2018 09:56 »
 Fine example of distortion there duTCh, if I may say so.

  The shells are also used on the later A50 and A65 crank as the Journals are the same.  Without an internal micrometer to measure the eye you can get a good estimate of condition by making your own go/no go gauge by turning up a washer or mandrel to the published size. Or a circle of card if you are a true backyard pioneer.

   Swarfy

Offline duTch

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Re: Large journal con-rod dimensions
« Reply #6 on: 15.10. 2018 11:04 »

 Hoping I won't need to be doing much of that ^^... I'm thinking how he may have mixed up the 4's with 9's, is by handwriting it  and maybe he or someone else typed it to the printer.... *dunno*
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

Offline Clive54bsa

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Re: Large journal con-rod dimensions
« Reply #7 on: 15.10. 2018 14:51 »
Thanks for all your input, looks like I'll be looking for a good machinist now, and the S.R. will be down for a while.
Good job I still have the G.F. running...............touch wood.
Clive


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Offline muskrat

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Re: Large journal con-rod dimensions
« Reply #8 on: 15.10. 2018 20:34 »
The problem with re-sizing by removing  metal from the joining faces (rod and cap) is it also reduces the rod length (ctr little end to ctr big end). OK only a couple of thou". I did this to shorten A10 rods by 2 mm to use in my A7SS racer with T160 pistons *eek*.
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Offline Clive54bsa

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Re: Large journal con-rod dimensions
« Reply #9 on: 16.10. 2018 03:20 »
looks like I'll have to get the crank pins reground too, it's on it's 3rd grind but it measures out at 1.655, .0015 under minimum. Darn it, It started as a minor job, replace the idler gear pinion and bushings, then I thought I'd split the case and clean out the sludge trap, oh well. Between my 2 A10's and a '98 XJ8 VDP with electrical issues, I'll have to put off the kitchen remodel  *smile*


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Re: Large journal con-rod dimensions
« Reply #10 on: 16.10. 2018 20:53 »
looks like I'll have to get the crank pins reground too, it's on it's 3rd grind but it measures out at 1.655, .0015 under minimum. Darn it, It started as a minor job, replace the idler gear pinion and bushings, then I thought I'd split the case and clean out the sludge trap, oh well. Between my 2 A10's and a '98 XJ8 VDP with electrical issues, I'll have to put off the kitchen remodel  *smile*

Generally it’s the pins wearing oval is the problem, sometimes them having a rough or grooved surface as well,  they don’t wear round, what difference are you seeing between diameters at 90 deg to each other? If you can’t see much difference it just MIGHT be your measuring equipment is at fault (or user error  *shh* ).
New Zealand

1956 A10 Golden Flash (1st finished project)
1949 B31 rigid “400cc” (2nd finished project)
1968 B44 Victor Special (3rd project,in progress)
2001 GL1800 Goldwing, well, the wife likes it
2007 KTM 950 Adventure, cos it’s 100% nuts