Author Topic: connecting rod bearing size confusion ( with pics)  (Read 11319 times)

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Offline gecko672

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connecting rod bearing size confusion ( with pics)
« on: October 12, 2011, 01:06:38 AM »
I know this post comes up so often but I haven't seen any that have these markings. I apologize in advance if this is just another stupid question.

Im having trouble working out my connecting rod bearing sizes. Ive found all the relevant data stamped on the crank weight and the engine case. The crank bearings were easy to work out, but the numbers on the side of my rods have me a little confused. On one side it reads 8/25 and on the other 1/4 ( 3 definitely say 1/4 but one looks kinda like it could be 2/4: I included a photo of that one).
Case : AAAAA
Crank: JL AAAAA
            PL 3333
The cranks work out to yellow. but the only number that makes sense on the rod  is the 1. which works out to yellow as well.
Am I doing it right? What do the other numbers mean? Any help would be greatly appreciated
 





There is a number and a letter stamped on the bottom of the rod but I was thinking that was the weight number.
CB750 1971 K1

Offline scunny

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Re: connecting rod bearing size confusion ( with pics)
« Reply #1 on: October 12, 2011, 01:10:32 AM »
doesn't look like factory markings. will sit back and look.
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Offline Bodi

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Re: connecting rod bearing size confusion ( with pics)
« Reply #2 on: October 12, 2011, 06:21:59 AM »
Raised numbers in a casting are always mold identifying marks and bear no relation to the final size, or even the weight except in a loose way. Size marks are punched, etched, scratched, or written on the part: there is no practical way to form raised letters on these small parts.
The marks pictured do not look like any factory mark I've come across. The factory marks I've seen are made with some sort of crayon apparently, how this survives years in hot oil I have no clue. Often they are so faded as to be unreadable.
I can't figure out what your marks might mean, either.
I suspect you have an engine that's been worked on a lot, so the markings are suspect. The case and crank marks should be right but possibly someone had the crank main journals polished which would obviate any markings.
Personally, first  I would plastigauge all the bearings to see if new shells are actually needed.
If you do need to replace them, I would buy one pair of shells each in the size you guess are right for the main and rod bearings, then gauge all the bearings one at a time. Use your existing shells in the other mains to centre the crank as you go. Once you know the clearance on all the bearings using new unworn shells you can select and order the shells you need.

Offline gecko672

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Re: connecting rod bearing size confusion ( with pics)
« Reply #3 on: October 12, 2011, 07:36:43 AM »
I did plasti guage one of the rod bearings and it came out at .051. I ran out of plasti gauge before doing the rest. So your thinking these rods may be aftermarket? Or the original number ground off and these engraved numbers put in place

I actually wasn't going to change them but when I took one of he rods off and looked at the bearing it was pitted and small pieces of the bearing were sitting inside. Kinda like it was delaminating. I can make out a very faint what I am guessing is a yellow mark now turned brown/tan with age on the side. I don't really have the luxury of buying two sets to compare so hoping some one has run across this before.
Thanks for your replies..
CB750 1971 K1

Offline crazypj

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Re: connecting rod bearing size confusion ( with pics)
« Reply #4 on: October 12, 2011, 07:47:21 AM »
To be honest, you are screwed.
 About the best thing you can do is torque end caps onto rods and have them accurately measured.
 You have the codes for the crank pins but none of the markings on rods are factory
 The service manual will have actual inside diameter of rids corresponding to code number.
When you have both numbers, you know which shells to buy
Is the 0.051 inches or millimeters?
Without specifying, it's a totally meaningless number
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Offline gecko672

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Re: connecting rod bearing size confusion ( with pics)
« Reply #5 on: October 12, 2011, 10:03:43 AM »
hey crazypj the .051 was in mm, id have way bigger problems if it was in inches me thinks :)
anyway I re read the posts and looks like I misunderstood Bodi's post. Yeah buying 1 set of a few colours looks like the way to go for me. I thought you meant buy a few complete sets.. dont mind me I hadn't had my coffee before replying.
Id still love to know if anyone has seen these markings before.
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Offline wrenchmuch

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Re: connecting rod bearing size confusion ( with pics)
« Reply #6 on: October 12, 2011, 03:21:48 PM »
I had the same figures on the rods in my K1 . I'm pretty sure that the 1 in 1/4 and 2 in 2/4 are your size numbers that you use in the Honda chart . I,d try 1 set of greens . That should fit the 2 rod 3 crank combination by the chart . You might find that its loose in that location . I've always found that the next size tighter from what the book says fits better , probably due to wear . I'm betting greens will fit the 1/4 combination and the 2/4 will need a set of browns .
Hope this helps
Mike
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Offline Bodi

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Re: connecting rod bearing size confusion ( with pics)
« Reply #7 on: October 12, 2011, 04:12:46 PM »
If you have access to a reputable engine shop, torquing the rod ends and having the bores measured as well as the journals will let you use the service manual chart to pick shells. I've had really poor luck with shops though... my instinct is to find a way to do it myself without spending a fortune on tools (a good bore gauge and the large micrometer to read it would be a big investment) so my first thought was to use plastigauge. I would measure the main journals and see if they agree with the marking, not a big job there. The case will be what the markings say: I don't think anyone would try to rebore the case main bearing bores.
I have picked up a few leads on good engine shops in Toronto but haven't had to use one lately. If anyone is near Brockville, Hewatt Automotive is excellent.

Offline crazypj

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Re: connecting rod bearing size confusion ( with pics)
« Reply #8 on: October 12, 2011, 05:30:04 PM »
I already have the tools and  know how to use them (I used to teach measuring/motorcycle repair machining)
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Offline gecko672

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Re: connecting rod bearing size confusion ( with pics)
« Reply #9 on: October 12, 2011, 10:19:57 PM »
hey wrenchmuch,
yeah this is off a K1 as well. Glad to hear someone else has seen this before. I think Im going to try a set of green and brown then plasti guage them see how that goes.
Crazypj ..now your just bragging :)
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Offline wrenchmuch

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Re: connecting rod bearing size confusion ( with pics)
« Reply #10 on: October 13, 2011, 07:30:59 AM »
Gecko : Where do you live ? If your close I've got a set of greens you can try .
Bodi : I use Gord Bush Performance in  Etobicoke .
http://www.gordbush.ca/
He bored my engine to 836 and did my head work . Couldn't be happier with the service .
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Offline crazypj

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Re: connecting rod bearing size confusion ( with pics)
« Reply #11 on: October 13, 2011, 08:32:41 AM »
Quote
Im having trouble working out my connecting rod bearing sizes.

Quote
I already have the tools and  know how to use them (I used to teach measuring/motorcycle repair machining)

You have the tools, you have the skill so best to use it.:)

The book has the bearing clearances and rod dimensions. I'd weight the rods for weight matching. I'd also make sure the caps match the rods as they are bored as a set. Someone may have tampered with the engine in the past after factory production. If you want a copy of the book for the data let me know.

rt

 except they are not my rods and I don't know where they are
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Offline gecko672

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Re: connecting rod bearing size confusion ( with pics)
« Reply #12 on: October 13, 2011, 07:12:44 PM »
thanks for the offer wrenchmuch but im in california.
I just ordered  1 set of greens and 1 of brown. I'll put them in the rods and per Bodi's suggestion, plasti guage them and see whats up.
I just got my main bearings and installed them last night.  The cases numbers said yellow so I replaced them with yellow and they plasti guaged  at .025mm Makes me think the engine hasnt seen that much abuse as these are the original size and the smallest of the bearings.
Hopefully the rods will turn out ok. Im taking bets on which colour the rod bearings turn out to be.
Im gonna go with greens across the board.
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Offline crazypj

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Re: connecting rod bearing size confusion ( with pics)
« Reply #13 on: October 13, 2011, 11:26:59 PM »
yup-my incorrect assumption.

 ;)
 At least we now know they are in Cali  :D
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Offline gecko672

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Re: connecting rod bearing size confusion ( with pics)
« Reply #14 on: October 14, 2011, 12:27:14 AM »
Hey crazypj. I see you have Florida an Wales in your avatar info. If your originally welsh good luck to your boys this weekend against the French. If your not this message may not make any sense. Maybe it will be a Wales v Aussie final at the rugby world cup. Go on the Aussies. :)
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Offline crazypj

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Re: connecting rod bearing size confusion ( with pics)
« Reply #15 on: October 14, 2011, 09:22:27 AM »
Welsh national game boyo,
I played fullback in school team, wasn't big enough though but mostly managed to get in peoples way  ;D
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Offline gecko672

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Re: connecting rod bearing size confusion ( with pics)
« Reply #16 on: October 14, 2011, 09:57:06 AM »
Bearings wont be in until tuesday.

Crazypj...Break away for me...Wales  deserves the finals. playing great rugby. I think the game is on around 11pm here on the west coast. I'll be watching it. One thing I always remember about watching wales play was the anthem, such passionate supporters.
   Pob lwc!

Welsh Anthem - Millenium Stadium
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Offline crazypj

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Re: connecting rod bearing size confusion ( with pics)
« Reply #17 on: October 14, 2011, 10:10:40 AM »
Now I'm homesick again  ;)
Totally off topic  8)
 
Wales became the first nation to sing a national anthem at the start of a sporting event
http://en.wikipedia.org/wiki/Hen_Wlad_Fy_Nhadau
 Every Welshman can sing (particularly in large groups  ;D)
Translation for the 'everyone not Welsh (just the first line in case you don't want to follow link) ;D
'The land of my fathers is dear unto me'

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Offline scunny

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Re: connecting rod bearing size confusion ( with pics)
« Reply #18 on: October 14, 2011, 02:03:27 PM »
looking forward to Wales v France tonight, hopefully the All Blacks kick Aussies arse tomorrow. looks like there will be more beers than wrenching this weekend.
oh yeah, back to the bearings.....
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Offline gecko672

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Re: connecting rod bearing size confusion ( with pics)
« Reply #19 on: October 14, 2011, 04:11:28 PM »
Ha.. if the aussie's get up this weekend I think you guys will just pull the plug and sink the islands. Either way I see a lot of beer, a lot of yelling and screaming and depending on the out come either utter devastation or ecstatic celebration and thats just me let alone you guys....
Good thing those bearings arent ready this weekend I'de hate to miss the boys giving the All Blacks a hiding :)
CB750 1971 K1

Offline Flying J

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Re: connecting rod bearing size confusion ( with pics)
« Reply #20 on: October 14, 2011, 04:32:37 PM »
Where did you order your bearings from. Its next on my shopping list.

Offline gecko672

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Re: connecting rod bearing size confusion ( with pics)
« Reply #21 on: October 14, 2011, 04:47:16 PM »
I ordered them locally from Honda in Glendale here. They said they are coming in from their warehouse, which is why its a few days out. It would have taken the same time ordering and shipping online.
Dynoman carries complete sets for a good price but he doesnt sell singles. I just needed one of each colour for now.
I do have a question though. The new main bearings seam way way softer than the ones that were in there. The new ones can be scratched with your fingernail. The old ones couldnt. What gives?
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Offline bryanj

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Re: connecting rod bearing size confusion ( with pics)
« Reply #22 on: October 15, 2011, 07:49:33 AM »
Old ones are "work hardened" so seem harder
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

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Offline gecko672

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Re: connecting rod bearing size confusion ( with pics)
« Reply #23 on: October 15, 2011, 07:51:45 AM »
Ah.. That makes sense.
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Offline 754

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Re: connecting rod bearing size confusion ( with pics)
« Reply #24 on: October 15, 2011, 10:55:11 AM »
 They may have an ultra thin coating on them to prevent corrosion, that comes off in run-in..
 
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