R90s Pushrod dilemma

[byron]

I'm in the process of rebuilding my 76 R 90 S. I have owned the bike for the past two years have spent just over a year slowly working through the rebuild. When I first of all bought the bike I purchase a new set of stainless steel pushrod tubes from motor bins and now I am poised to install them. All my engine parts are away being cleaned and I'm just checking I've got everything ready to reassemble next week.
However when I come to measure old pushrod tubes against the new stainless steel ones there is a big discrepancy. All of the old tubes are around about 17.7 mm to 17.90 in diameter. The stainless steel ones are 17.9 mm on average in diameter. I have measured all with a vernier and micrometer but the photographs show the vernier for detail. My question is where do I get an accurate set from because clearly
0 .19 mm is clearly too much for a shrink push fit.

 

[cookie]

the set i fitted, i put the barrels in the oven, tubes in the freezer packed with ice, and still an utter bastard to get in.

hope you bought the fitting tool

 

[Rob Farmer]

Surely the 17.9 of the stainless is the same 17.90 as your old ones. Have you measured the id yet?

 

[oldenoughtoknowbetter]

Didn't 1970 to 1975 use a different diameter tubes to the later years?

 

[byron]

Didn't 1970 to 1975 use a different diameter tubes to the later years?

Yes that is correct but I have a 76 bike. It was a typographical error on my part and the size is 17.79 max for the old set and as I stated 17.9 to 17.98 for the new set . In the past whenever I have tried to create interference fit the tolerances used are no more than 0.04mm approximately . My worry is that up to 0.16 to 0.19 mm is just too much for interference fit. Unfortunately I do not have an internal Micrometer or a plug gauge to be able to measure the holes in the barrel. Are all the new tubes inaccurate or is it a firm that I can rely on?

The old tubes came out with heat but clearly heating and chilling will not let an almost 0.2mm interference fit!

 

[lawvar]

Where are you in the uk as my dad may be able to help he is a retired precision engineer

Sent from my SM-G920F using Tapatalk

 

[Rob Farmer]

Most of the stainless pushrods tubes available are made using standard tubing. If you measure the tube thickness it's much too thick and can catch the pushrods.

Get in touch with Keihan and ask about theirs. I'm not sure if they make them for your year but it's just a phone call.

 

[Sean Kelly]

Can't you just get them machined down?

 

[ChasF]

I read somewhere (probably ADVrider) that the ones from Chris Shaw Engineering are a better fit.

 

[byron]

Thanks for all the advise I will try and sort something next week

 

[byron]

Thanks for all the advise I will try and sort something next week

Well chaps it all seems to have worked out quite nicely. I contacted Chris Shaw and he gave me confirmation of some very accurately machined pushrod tubes. He is such a helpful chap and measured them on the phone for me to confirm the sizes for my 1976 bike. And they arrive within 24 hours, what could be better. I would recommend anybody use him rather than the two main suppliers we tend to use. He also confirmed that there have been lots of problems with these suppliers . My final question is how far to insert them? Should the inside edge of the flange be level with the bottom edge of the barrel flange? Does anyone have a photo of that detail?
Thanks