600 cod rods in 650 engine

LynP · Post by **LynP** » Sat Apr 02, 2011 9:31 pm

I am fitting earlier 600 rods into my 1961 650 matchless. I have put the two chamfers on the sides of the eyes on the rods to clear the crankcases and from the articles I have read, I believe that I need to modify the end caps as well. I have studied the end caps of the rods from the early engine and the the end cap from the undamaged rod from my 650 engine, but cannot fine any noticeable difference. Please can anyone explain exactly how I need to modify the cap, where do I remove the metal from? (I know the rod from my engine was the one put in when the bike was made and so is correct for the engine so I am not looking at another incorrect rod) Any help will be appreciated.

Eric · Post by **Eric** » Sun Apr 03, 2011 12:25 am

You are in territory that I don't understand i.e. above 500cc but I cannot see why using 600 rods in a 650 engine would require any modification to the caps.

Both engines have the same bore, but the 650 has a longer stroke, so the only part of the rods that should need change is above the caps and you have done that already.

My concern is that after so many years of existence the rods develop a very strong skin very similar to ourselves in an ageing process, breaking that skin can weaken the casting, apparently the cure is to highly polish the wounded area to remove scars.

Sounds a bit like some of the treatments the plastic surgeons do for vast amounts of money to ladies who should know better.

wilko · Post by **wilko** » Sun Apr 03, 2011 5:21 am

It was the later beefier rods that had these chamfers so your 600 rods dont need modding.

LynP · Post by **LynP** » Sun Apr 03, 2011 12:19 pm

Thank you for the replies. As far as polishing the new chamfer is concerned I can do that easily and perhaps it is better to be sure given the ease of the task.

In relation to the beefier rods what year did these come into use. I think my 600 rods came from a late 600, I took them from a 1957 G11 motor years ago and the 650 one is from my G12 engine made in 1961 which I stripped in the early 1970's. (A very long term project!) The only differences I can see are the chamfers I have done and the cap on the 6oo rods is better finished, smoother on the end of the cap than the 650 one.

wilko · Post by **wilko** » Mon Apr 04, 2011 1:00 am

Lash out and buy some Ridgecrest rods.

LynP · Post by **LynP** » Mon Apr 04, 2011 8:51 pm

I would like to buy new rods, but the funds I have to use on the bike means that I need to use the good rods I have if I want to get the bike completed.