which bronze is used

[nicolas]

i have been looking at the possibility of fitting new bronze lifter guides in my case and i can't seem to figure out which material to use, or what is the correct clearance when cold. the reason being the copper and bronze usually expands more then metal. i am also wondering what fitting you would suggest when i machine the case and the inserts.

thanks

[ibg]

I can't advise on the material to use, though rocky Jennings sells silicone bronze bushes. I did some testing on my sleeved case in the oven, and the bores expanded much faster than the lifters, so i would suggest very close clearance, around 1 thou. A lot will depend on your ambient temperature on start up, over here in Melbourne Australia in is not less than 12 deg C. so at 12 deg I have 1 thou clearance. If your startup temps are colder you may need more clearance.

[K-Roc]

Ampco 45     Nickel -Alum-Bronze

Also makes unreal valve seats. 

Here's a good link to info on the material

http://www.matweb.com/search/DataSheet.aspx?MatGUID=388203f1c3034fb8b0362c3f7cdd6e46&ckck=1

Cheers.  K-Roc.

[nicolas]

thank you.

so to get this right a clearance of 1thousanth is 0,0254 mm? i looking at temperatures in the average of 20°C up to 30°C when cold. but that can't be decisive on engine 'needs'. the clearance needs to be right to keep enough oil pressure and allow lubrication.

and what fitting is used to press them in the case. case heated up and dropped in or pressed in? 

[didi]

Hi
have a look at the end of this blog page.
http://didivw.blogspot.com/search?updated-max=2011-03-13T15:30:00%2B01:00&max-results=7&start=7&by-date=false

cooled the sleeves down and heated the case up.

Didi

[Bruce]

  i would suggest very close clearance, around 1 thou.

Better than guessing is to use VW's spec.
Lifters: 18.96-18.98mm
Bores:  19.00-19.02mm

[ibg]

Whilst Bruce's, suggestion is good, the VW specs are fairly wide, from .02mm to .06mm, my testing led me to work on the close side, 0.025mm is about 1 thou. When my case was at operating temp there was 4 thou clearance between the lifter and bore (0.1mm). I would suggest reaming or preferably honing the lifter bores to size after fitting the bushes. I found small differences between lifters and honed to suit.

I didn't fit my bushes, but I have read that only 1 or 1.5 thou interference should be used when fitting the bushes due to the chance of cracking the case, a machinist may be able to advise you. I like the idea of heating the case/chilling the sleeves and pressing them in easily.

[didi]

What is even helpful for an easy and fast starting to the press in procedure, machine a small diameter lead on the bronce sleeve of about 2mm long and a couple of thousandths under size

Didi

[nicolas]

thanks for all the info. i think i stick to Bruce's advice and take the smallest clearance as a starting point i should be Ok.
and yes i was thinking of honing them to the right size afterwards, or machine them to the exact size. . the idea of a stepped bushing can work as well, but it should be OK with a good chamfer.