Valve clearance thoughts - Page 3 - Triumph Forum: Triumph Rat Motorcycle Forums
Twins Technical Talk Technical Talk for Hinckley Triumph Twins: Bonneville, T100, Speedmaster, America, Thruxton, and Scrambler.
Sponsored by: Long Beach Motorsports

LinkBack Thread Tools Display Modes
post #21 of 24 (permalink) Old 11-05-2012, 02:04 AM
Senior Member
Supersport 600
Main Motorcycle: TT140
Join Date: Aug 2012
Location: NY/LA
Posts: 161
Tas, Nice X to Y parts.

Valve clearances:
1. Factory lash has a min and a max number. The normal aim is called "blueprint." Better known as is the [middle] valve lash number you aim for. Say nothing wears. We'll get back to that later. For now, we can see 3 distinct lash settings. Setting this number gives the best performance.
2. Factory maximum will be the wide side. Wide means longer seat time. Cooler running. Slow power. Waiting for the last diminishing return; is the valve sitting closed [longer] in the power stroke. This also means grunt. It is not as near the better [blueprint] performance number.
3. Factory minimum gap is to get away with the narrowest number. Hotter seat time. Faster is the event to occur sooner. You cut off the power sooner with the valve being tighter. The intake opens sooner to make things occur faster on the intake side. The power down is the exhaust opens sooner, so the intake cycle happens faster. This is more for top end work. High rpm, not street grunt with the wide gap.

Back to the blueprinted number is that middle shot at both grunt and top. Cool, you build carbon. The middle number, you burn off carbon and remain book hot. The tight valve is burning off the carbon and cooking itself too, is too short a sit time. Not recommended for the long haul touring stuff. Tight is for race.

Now the wear factor:

A. Cams are shrinking or being compressed like shot peening it. There is a gap or growth on the wide side.
B. Cam towers are compressing too via the valve spring tension. These contribute to a wide gap at the lash.
C. The valve tip can mushroom, not slide out of the valve guide, but hang up. This too causes a wide valve lash.
D. The valve is harder material, can hammer the seat past its narrow 45° valve area. This mushrooming on this end can cause the valve lash to go tight.
E. The hard valve seat can hammer the softer aluminum head. This moves the whole seat up into the head. This can cause the valve lash to narrow.
F. The valve itself can burn, lose its 45° angle, become mushroomed and move up towards; narrowing the valve lash.
G. The shims can hold their tolerances. They may not contribute to a clearance problem.
H. Under the shim bucket, the contact point over the valve tip; This is also some pretty hard material like the shim. This can hammer the valve tip, but would crack at that small a rise. I would assume this holds its contact point harder than the [mushroomed] valve tip and may not cause a clearance problem.

When tight, my experience shows they tick some than when loose.
The valve check is done by using a go-no-go system. If for argument sake, the narrow gap was .002" and a .003" could not fit in between, you are within spec. If for argument sake the widest gap was .004" and a .005" would not slide in, you are again, within clearances using the go-no-go method.
TT140 is offline  
Sponsored Links
post #22 of 24 (permalink) Old 11-05-2012, 03:29 AM Thread Starter
Senior Member
Grand Prix 500
Main Motorcycle: Bonneville
Join Date: Oct 2010
Location: Tasmania
Posts: 131
Other Motorcycle: Honda Postie
Extra Motorcycle: Suzuki DL650 V Strom
Cool reply.......or hot, depending on valve clearance! What you say gives some credence to the anecdotal view that a hard ridden bike results in tightening valve clearances and a carefully ridden bike (eg touring) results in increased valve clearances, mainly I would think due to increased stress on the valve seat area at higher revs. Your comments make me comfortable with my re shimmed clearances (I measured them all) of 0.2 on all inlets and 0.28 on three exhausts and 0.27 on the fourth. Thank you for your thoughtful post.
Tasmaniablue is offline  
post #23 of 24 (permalink) Old 11-11-2012, 12:05 AM Thread Starter
Senior Member
Grand Prix 500
Main Motorcycle: Bonneville
Join Date: Oct 2010
Location: Tasmania
Posts: 131
Other Motorcycle: Honda Postie
Extra Motorcycle: Suzuki DL650 V Strom
My Bonnie is back together and new PVL coil fitted. Completion of the work was delayed due to illness, I am ok now.........I think. Bike fired up immediately and runs smoothly. Will ride it on a hot day to see if my ignition fault reappears. If it does I will fit a Procom igniter. Thanks for all your comments, most helpful.
Tasmaniablue is offline  
post #24 of 24 (permalink) Old 11-11-2012, 09:01 AM
Senior Member
World SuperBike
Main Motorcycle: Triumph Thruxton EFi
Join Date: Nov 2010
Location: Preston, North West UK
Posts: 1,934
Other Motorcycle: Yamaha R1, Honda CB1000R
Originally Posted by TT140 View Post

A. Cams are shrinking or being compressed like shot peening it. There is a gap or growth on the wide side.
If the area of the cam you are measuring to is wearing then you've got big problems, the whole point of the clearance is that this part does not touch the shim.
GDCobra is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Triumph Forum: Triumph Rat Motorcycle Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter your valid email address, that can receive an automated confirmation message. Otherwise, you won't be able to gain full access.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Similar Threads
Thread Thread Starter Forum Replies Last Post
adjusting valve clearance drop a valve shim button GRANDPAamerica Twins Technical Talk 25 06-27-2012 10:35 PM
Valve Clearance fat frank Twins Technical Talk 5 02-02-2010 11:34 AM
Valve Clearance Don x 3 Trophy 7 08-06-2009 12:40 AM
Rocker arm clearance/valve clearance... whatever you want to call it. double-d Club Cafe' 4 04-04-2008 09:41 AM
Valve Clearance at 24K sidreilley Maintenance & Workshop Talk 1 03-31-2004 10:33 AM

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 Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On

For the best viewing experience please update your browser to Google Chrome