The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: SimonHolyfield on 17.03. 2019 20:02

Title: Rods 101
Post by: SimonHolyfield on 17.03. 2019 20:02
Here we have two large journal A10/FH rods, for my Huntmaster. You'll have followed the sows ear to silk purse crankshaft story - these are the next bits.

They have the same part number - neither has the oil hole.

I've cleaned them, removed the caps and bolts, checked for cracks. I've not looked at the small ends yet. I guess I'll make some mandrels to check for straightness, and they will need new bolts...

What else?
Title: Re: Rods 101
Post by: RDfella on 17.03. 2019 20:11
Whilst I would usually recommend fitting new big end bolts with a rebuild, how - following on from the thread on cam followers - can you be sure new ones will be as good as the ones you have?
Title: Re: Rods 101
Post by: SimonHolyfield on 17.03. 2019 22:41
Good point.

I fitted a new set of big end nuts to a Square Four a few years back, and one stripped during initial torquing. I replaced them all, but still worry about it...
Title: Re: Rods 101
Post by: berger on 18.03. 2019 00:43
ARP are proper big end bolts and nuts if you want to spend money on something that is what it is for a change--- proper ...edit check big end eyes for ovality and polish all those little nicks and bruises out
Title: Re: Rods 101
Post by: vinver on 18.03. 2019 02:27
Hi Simon,
A quick way to check straightness-  Use a gudgeon (wrist) pin , put both rods on it. If they mate up together, great. Now flip one rod over, they should be still parallel . Flip the other rod over and should still be matched. You can assess the wear on the small ends at the same time, make sure  small end bushes haven't rotated and oil hole is oriented correctly.  One of your rods should have an oil drilling at big end- looks like you have two right hand rods.  Cheers, Vincent
Title: Re: Rods 101
Post by: Swarfcut on 18.03. 2019 09:24
Simon, Both the caps and rods should not rock when their joint faces are placed on a flat surface. The side of the big end and small end eyes are machined at the same time, so should be in the same plane, the flat surface check again, a simple test for twisting. The bearing locating cutouts can suffer fretting from loose shells.

 The two rods on a single pin trick, thanks Vincent, does the check for bending. A nicely polished rod removes the likely starting points for failure, and is satisfying to do as well as going some way to matching the rods for weight.
   The rods should weigh more or less the same, you are lucky if they match exactly with an unknown engine. The damage to the side of one of the big end eyes looks like a sign of some harsh treatment, so as bergs says, check for ovality.  Standard eye size for a big journal crank is 1.8435"/1.8440"

Title: Re: Rods 101
Post by: SimonHolyfield on 18.03. 2019 23:00
Some good pointers there folks, thank you. If I get near the workshop tomorrow I will report back.

Anyone see the need for me to drill the missing hole? I guess BSA didn't put it there for fun...
Title: Re: Rods 101
Post by: Swarfcut on 19.03. 2019 08:37
Simon..  Just search Conrod Oil Hole on the forum. Almost all you need to know about the hole is there. I would be inclined to discard your scuffed rod and source a correct drive side rod, or even a "matched pair".  It all depends how much you can be tempted to punt into this project.