The Spares Company
Club Shop/Regalia
Parent Website
Contact Officials
Machine Registrar
Club Secretary
Membership Secretaries
MPH Editor and Forum Administrator.
Section Newsletters
Technical Databases
Photos
Home
What's new
Latest activity
Forums
New posts
What's new
New posts
Latest activity
Information
Bike Modifications
Machine Data Services
Manufacturers Manuals
Spare Parts Listings
Technical Diagrams
Whitakerpedia (Vincent Wiki)
The Club
MPH Material Archive
Flogger's Corner
Obituaries
VOC Sections
Local Sections
Local Section Newsletters
Miscellaneous
Club Assets
Club History
Club Rules
Machine Data Services
Meeting Documents
Miscellaneous
Essential Reading
Magazine/Newspaper Articles/Letters
Adverts and Sales Brochures
The Mighty Garage Videos
Bikes For Sale (Spares Company)
Log in
Register
What's new
New posts
Menu
Log in
Register
Install the app
Install
Home
Forums
Forums: Public Access
Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
ATD Advance Timing Curve?
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="Martyn Goodwin" data-source="post: 51678" data-attributes="member: 2433"><p>Excellent bit of explanation Max. Here are 3 photos of the failed piston from my Comet. No sign of melting of the piston - The top compression ring groove has actually opened up, a section of the top ring has broken off and been wrenched upwards and out of the groove - I assume it eventually went out the exhaust. That bit of broken ring scored the bore beyond repair and also badly damaged the exhaust valve and seat.</p><p></p><p>The second compression ring groove has collapsed trapping the ring and preventing it from applying any pressure on the bore. It was only the oil ring that kept the motor running! And it ran in this condition (photos) for around 400 miles till I got back home (it was the last leg of a 3 day 1,300 mile trip) and was able to strip down the motor and start repair work. In case you wondered, its (or was) a CP piston. Oil use during those last 400 miles was high due to the excessive crankcase pressures resulting from the failure of both compression rings.</p><p></p><p>I was advised that the light grey/white ash deposits on the piston crown indicated that the mixture (thus the carb jetting) was just about spot on. The reason I moved down a size on the needle jet was to reduce fouling of the spark plug at moderate speeds/throttle openings.</p><p></p><p></p><p></p><p> [ATTACH=full]2416[/ATTACH] [ATTACH=full]2417[/ATTACH][ATTACH=full]2418[/ATTACH]</p></blockquote><p></p>
[QUOTE="Martyn Goodwin, post: 51678, member: 2433"] Excellent bit of explanation Max. Here are 3 photos of the failed piston from my Comet. No sign of melting of the piston - The top compression ring groove has actually opened up, a section of the top ring has broken off and been wrenched upwards and out of the groove - I assume it eventually went out the exhaust. That bit of broken ring scored the bore beyond repair and also badly damaged the exhaust valve and seat. The second compression ring groove has collapsed trapping the ring and preventing it from applying any pressure on the bore. It was only the oil ring that kept the motor running! And it ran in this condition (photos) for around 400 miles till I got back home (it was the last leg of a 3 day 1,300 mile trip) and was able to strip down the motor and start repair work. In case you wondered, its (or was) a CP piston. Oil use during those last 400 miles was high due to the excessive crankcase pressures resulting from the failure of both compression rings. I was advised that the light grey/white ash deposits on the piston crown indicated that the mixture (thus the carb jetting) was just about spot on. The reason I moved down a size on the needle jet was to reduce fouling of the spark plug at moderate speeds/throttle openings. [ATTACH=full]2416[/ATTACH] [ATTACH=full]2417[/ATTACH][ATTACH=full]2418[/ATTACH] [/QUOTE]
Insert quotes…
Verification
What was Mr Vincent's Christian Name?
Post reply
Home
Forums
Forums: Public Access
Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
ATD Advance Timing Curve?
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
Accept
Learn more…
Top