Go Back   ADVrider > Bikes > Old's Cool > Airheads
User Name
Register Inmates Photos Site Rules Search Today's Posts Mark Forums Read

Thread Tools Search this Thread Display Modes
Old 04-16-2012, 03:36 PM   #16
Old Enough To Know Better
mark1305's Avatar
Joined: Feb 2005
Location: Merritt Island, FL
Oddometer: 6,091
Originally Posted by disston View Post
Talking about valve push rod tubes, not guides....snip...

Sorry I wasn't more clear on the analogy, but valve guides are way more robust than the tubes and even with a proper mandrel, it can be easy to ding or bend them up while driving them into position. Even with heated heads and frozen guides. DAMHIK.

P/R tubes, being more fragile, present an even greater opportunity to screw up.

However, given the success stories posted so far, I feel better should I have to do any of mine one day.
Mark J
Merritt Island, FL

When a person asks you for advice, they don't want advice. They want corroboration.
mark1305 is offline   Reply With Quote
Old 04-16-2012, 05:13 PM   #17
Gnarly Adventurer
Velocipede's Avatar
Joined: Mar 2006
Location: Kingston Ontario Canada
Oddometer: 471
I've given this problem a lot of thought over the years that I've owned and wrenched on Airhead Beemers.I am far from being a BMW Guru as some of the inmates undoubtably are but it occurs to me,where were the heads of the BMW engineers when they redesigned the motor and moved the pushrod tubes from over to under the cylinders.Why didn't they forget the tubes altogether and just cast the pushrod tubes into the cylinders.

I've owned Triumphs and BSA twins over the years and I've always found that it was easier to build an oil tight motor on a BSA with cast in pushrod tubes than a Triumph with external tubes.

Velocipede is offline   Reply With Quote
Old 04-16-2012, 05:21 PM   #18
disston's Avatar
Joined: Mar 2011
Location: Silver Spring, Md
Oddometer: 10,218
I'll bet the reason is weight reduction. I don't know this for fact but think cast in passages would mean more weight.

The reason for moving the cam shaft from above the crank to below I don't know. I think I might have heard why that was but I forgot.

Crank on bottom was a selling point I think. My friends who rode /2s would tell me the center of gravity was lower.
Never memorize something you can look up.
---Albert Einstein

Pay your debt, piratejohn.
disston is offline   Reply With Quote


Thread Tools Search this Thread
Search this Thread:

Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump

Times are GMT -7.   It's 01:35 AM.

Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2015