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#553549 - 07/18/14 4:01 pm con rod big end roller 'play'  
Joined: Sep 2013
Posts: 1,583
quinten Online content
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quinten  Online Content
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Joined: Sep 2013
Posts: 1,583
Pacific northwest

My 67 T20M's con rod has what appears to be a roller-bearing big-end

How much , if any , up and down play is acceptable ? ( I'm not dying to split the cases)
There is discernable play , quite a bit side to side and I'd guess around 0.1mm
In and out
.

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#553553 - 07/18/14 4:30 pm Re: con rod big end roller 'play' [Re: quinten]  
Joined: Feb 2011
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Boomer Online content
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Boomer  Online Content

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Joined: Feb 2011
Posts: 3,354
Orygone
Not familiar with the tolerances for the Cub's but the big singles are not supposed to have any up and down play.

Wasn't that late Cub roller big end like a needle roller?


Bill B...


Boomer
#553577 - 07/18/14 5:56 pm Re: con rod big end roller 'play' [Re: Boomer]  
Joined: Dec 2004
Posts: 8,893
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,893
Scotland
No up and down, side to side is easily confused with it but side to side is ok.

#553582 - 07/18/14 6:17 pm Re: con rod big end roller 'play' [Re: quinten]  
Joined: Mar 2005
Posts: 9,970
John Healy Online content
John Healy  Online Content


Joined: Mar 2005
Posts: 9,970
Boston, Massachusetts
If my calculator is right .1 - .0039". I need to use one of Stuart's shocked to express my feelings.

.001" would be more like what you were looking for to be cool


#553633 - 07/19/14 12:55 am Re: con rod big end roller 'play' [Re: John Healy]  
Joined: Dec 2004
Posts: 8,893
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,893
Scotland
Using just feel you start to detect play at 3 thou, so once you can feel it by pulling and pushing on the rod you are at a minimum of 3 thou play.

#553688 - 07/19/14 9:12 am Re: con rod big end roller 'play' [Re: quinten]  
Joined: Mar 2005
Posts: 9,970
John Healy Online content
John Healy  Online Content


Joined: Mar 2005
Posts: 9,970
Boston, Massachusetts
Kommando is right and you can experience this when adjusting Triumph rockers to .002" intake and .004" exhaust.

At .002" there is no vertical movement, but the rocker will slide freely side to side against the spring.

As you approach .004" clearance you will begin to feel vertical rocker movement and at .004" you will hear and feel the rocker "click." This can be verified using a dial indicator.

.002" vertical movement on a Cub rod is the absolute upper limit. While the engine will continue to run with a rod with more than .002" vertical clearance it is not if it will fail, but when.


#553713 - 07/19/14 12:02 pm Re: con rod big end roller 'play' [Re: quinten]  
Joined: Oct 2012
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run990 Offline
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run990  Offline
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lancashire united kingdom
tiger cub big ends are a weakness ,place a feeler gauge down the side of the big end eye that just takes up any side float.blast a load of petrol into the roller cage to remove any stiction from oil.then test for up & down play at various positions during rotation.if its suspect change it before it wrecks the rod.

#553717 - 07/19/14 12:32 pm Re: con rod big end roller 'play' [Re: quinten]  
Joined: Aug 2001
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D.Bachtel Online content
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SLO County, CA
Alpha made a rod/roller bigend conversion to replace the plain shells.
Any Cub run hard needs one.
As the first unit single these engines are lucky to have bushings at all.


Don in Nipomo

#553738 - 07/19/14 3:30 pm Re: con rod big end roller 'play' [Re: run990]  
Joined: Sep 2007
Posts: 1,073
gREgg-K Online content
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gREgg-K  Online Content

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Ottawa, Canada
Originally Posted By: run990
<SNIP> blast a load of petrol into the roller cage to remove any stiction from oil. then test for up & down play at various positions during rotation.if its suspect change it before it wrecks the rod.

Run990 makes two good points that warrant repeating with the "reason why",in case they get missed. Big ends do not wear uniformly because of the reciprocating loads they carry, and also, the presence of oil in a bearing will mask wear.

So be sure to check the bearing dry, and inspect for slop at every orientation you can manage ... while it may 'feel OK' in one position, it may be beyond its allowable limit at a more heavily loaded position.

... Gregg


Spyder Integrated Technologies
Lucas, BTH, & Miller Magneto & Dynamo Restoration
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#553822 - 07/20/14 4:02 am Re: con rod big end roller 'play' [Re: gREgg-K]  
Joined: Sep 2013
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quinten Online content
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quinten  Online Content
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Joined: Sep 2013
Posts: 1,583
Pacific northwest

Some late model Cubs came with a roller big-end , others may have been fitted with one over time. I have yet to see mine .



I have blasted it with wd40 ( to de-oil) and more than triple checked it from multiple positions , its not so easy to isolate the side to side from the up and down
On a roller bearing you cant see ... so I placed a wood 1x1" against the conrod , front to back on the engine case , to minimize lateral movment ... and can "feel" consistant slight movement , up and down , from all positions where the little end is high enough to work with ... and hear the slightest ' tink -tink' as the rollers move in their races . No spots feels bad , different or worse than any other , but the amount of play is disheartening.

The p.o. installed a poorly-fit under-sized 10:1 piston in the cylinder with no discernable hone , which allowed front and back scoring of both the piston and bore ... and just tonite , on closer inspection , I now see how
The original over sized intake valve , for this model , has " kissed" this new high-dome piston . I now see why the
P.O. could not get it running "right" ... i am slowly getting used to the idea of having to split the cases on this low mileage bike ... and my growing 'things to buy list'

#553858 - 07/20/14 9:02 am Re: con rod big end roller 'play' [Re: quinten]  
Joined: May 2013
Posts: 4,533
Allan Gill Offline
Allan Gill  Offline



Joined: May 2013
Posts: 4,533
Rotherham - S. Yorkshire
Fit the lower cr piston for a start. I fitted a Todd racing head to the D14 once. The head was designed for the low cr d7 but I placed it on a already 10:1 piston. It didn't run any better just became a bit noisier on the bearings.

I'd suggest if your in any doubt of the big end, get it done. That way you know it's right and will give you many years of good service. Otherwise you'll be preying for that bit between your legs in the hope it doesn't fail you ( the engine i mean wink )


beerchug

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