The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: paulc67 on 24.02. 2014 20:06

Title: timing bush
Post by: paulc67 on 24.02. 2014 20:06

Anyone  *????*the size of the crank is 1.355 would that be  +10 or +20 needed for the bush *conf*

Title: Re: timing bush
Post by: wardleybob on 24.02. 2014 21:09

Hy paulc the standard size of a small journal crank is 1-455 so you are +10 .I would get a standard
Bush to allow you to line ream to size Wardleybob .

Title: Re: timing bush
Post by: wardleybob on 24.02. 2014 21:34

Ht paulc67 sorry you need a plus 20 to give you something to ream out .I went the wrong way in my last reply.wardleybob

Title: Re: timing bush
Post by: RichardL on 24.02. 2014 22:26

Uhhh,  the numbers aren't quite right.  Sorry,  can't provide more info from here on the train.

Richard L.

Title: Re: timing bush
Post by: Briz on 24.02. 2014 23:36

Bob; I think the size you quoted, 1.455 (?  isn't it 1.4375?) is the bigend size. The timing side main is 1.375" as standard. So Richards crank is at -.020"

Title: Re: timing bush
Post by: RichardL on 24.02. 2014 23:44

Briz,

Let's keep my crank out of this.  Paul's is the issue (though I think mine is also -20).

Title: Re: timing bush
Post by: paulc67 on 25.02. 2014 18:06

thanks bob so +20, my book says standard is 13735
Paul

Title: Re: timing bush
Post by: Briz on 25.02. 2014 19:34

Quote from: manosound on 24.02. 2014 23:44

Briz,

Let's keep my crank out of this.  Paul's is the issue (though I think mine is also -20).

Duh! sorry! *red*

Title: Re: timing bush
Post by: RichardL on 25.02. 2014 21:54

Paul,

Given that your bush journal is now 0.0185" under standard, going with a -0.020" bush means you are limiting your machinist to about 0.0025" to 0.003" of meat to work with when boring the new bush to fit, assuming you don't grind the journal first (which, I think, amounts to about the same thing). This seems like a problem to me, but I am no master machinist (furthest from it, by other recent admissions).  Now, supposing you go with a -0.030" two-part bush without grinding the journal, you will be removing a lot of the inner bush material, which also seems like a problem. My thinking is that a -0.030 solid, one-piece bush gives you the best opportunity to keep the journal as it is or grind it to clean-up only. Then, the bush can be bored and honed to a close fit.

EDITED: Now, here's the most important part: let's wait to hear from a few others before believing a word I've said. 

Richard L.

Title: Re: timing bush
Post by: RichardL on 26.02. 2014 03:47

Guys:

I edited my last post about Paul's timing bush so you won't feel self-concious about chiming in. So, please chime in.

Richard L.

Title: Re: timing bush
Post by: paulc67 on 26.02. 2014 18:01

thanks manosound but i ordered the +20 bush last night, i will get the engineering company to look at it on friday and see what they think

Title: Re: timing bush
Post by: RichardL on 26.02. 2014 19:28

I'll be interested to hear what he says. My advice is: don't put it in the crankcase until he guarantees he can keep the clearance within spec. That way you have a chance to return it.

Title: Re: timing bush
Post by: paulc67 on 27.02. 2014 21:00

i will try that tomorrow and see what they say, all the cam didnt turn up any way so if he says its too small i can return it for a bigger one
Paul