con rod / big end wear

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
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Matchymarty
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Posts: 202
Joined: Sun Oct 25, 2015 8:19 am
Location: AUSTRALIA

con rod / big end wear

Post by Matchymarty »

Hi all,

Apologies for a question that may have been asked before. I can't seem to find what I'm looking for in the searches.

In determining big end wear, is it acceptable for the con rod to flop side to side like a pendulum about the big end as a pivot? I can't detect much if any up and down give in the big end, but, there is some side to side movement between the fly wheels (normal?) but the con rod does wobble side to side about 1/2".

Am I up for a new big end?
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clive
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Posts: 5657
Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: con rod / big end wear

Post by clive »

If we are talking about a single its up and down movement that counts. Do check it when the rod is at tdc though as it may be worn there more than elsewhere.
clive
if it ain't broke don't fix
bjorn
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Posts: 69
Joined: Mon Jan 01, 1990 12:00 am
Location: NORWAY

Re: con rod / big end wear

Post by bjorn »

On a freshly built crank, side to side "rocking" of the small end is less than 2mm. Your big end has considerable wear. The 1/2 " total movement indicates that radial bearing clearance is almost 0.5mm. You should be able to feel this as up and down play on the con rod.

Bjørn
Matchymarty
Member
Posts: 202
Joined: Sun Oct 25, 2015 8:19 am
Location: AUSTRALIA

Re: con rod / big end wear

Post by Matchymarty »

bjorn wrote:On a freshly built crank, side to side "rocking" of the small end is less than 2mm. Your big end has considerable wear. The 1/2 " total movement indicates that radial bearing clearance is almost 0.5mm. You should be able to feel this as up and down play on the con rod.

Bjørn

Thanks Bjorn. The manuals don't have knowledge like this! I'm learning a lot with these bikes! :)
Marty
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