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Author Topic: Valve job - better breathing  (Read 493 times)

Chasfield

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Valve job - better breathing
« on: April 14, 2012, 06:33:48 PM »
I have just installed one of Hitchcocks oversized, high quality 43 mm exhaust valves in my 500 classic. This is made of higher quality material and has a better gas flowing profile (flatter backed, not so tulip shaped - it should generally block up the exhaust port less). It also features a waisted lower stem.

Along the way, I did a proper blend and smooth of the head casting where it meets the hardened valve seats. There was a massive step in the exhaust port where these areas met, and a smaller but significant one on the inlet side. I just had to get rid of these ghastly flow blockages, given that the port area close in by the valve seat is said to be the bit that matters most when porting a head, I smoothed away other sundry lumps and bumps in the exhaust port but left the inlet side well alone for fear of doing more harm than good. Though I did blend the carb. stub manifold and heat proof gasket into the inlet port, since there were pronounced steps between these three components.

The valve itself is larger than the stock one, which Hitchocks reckon to be undersized and therefore liable to poor sealing. The new valve is noticeably bigger. In fact, I was slightly nervous about piston clearance so I relieved and profiled the piston striking edge of it a tad, until it gave the same drop to contact with the piston distance as the stock valve. Probably unnecessary but once I get an idea in my head...

I gave the valve a light lapping, The contact ring is of good width and noticeably larger diameter than the one on the stock valve.

What was the outcome of all this activity? Well, I've got good compression. I can stand on the kickstart now. There was actually more of an exhaust "blat" when I kicked the engine over, ignition off - which I took to be a promising sign. On the road, the exhaust note is a good bit louder and it has a snarl to it that wasn't there before. It also breathes noticeably better at high rpm - such that there is now some point to holding onto third gear. Before it was better to get into top early and use torque rather than revs to get a move on.

I am quite pleased with the outcome, given the 50 GPB spent on parts and gaskets. This was probably a better place to start than bunging a bigger, flat slide carb on such a rough hewn cylinder head as mine.
« Last Edit: April 14, 2012, 06:40:54 PM by Chasfield »
2001 500 Bullet Deluxe

ace.cafe

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Re: Valve job - better breathing
« Reply #1 on: April 14, 2012, 07:44:45 PM »
Good show!

A good valve job and blending away obstructions can be one of the most productive things you can do.
Happy that it worked out well for you, and has improved your pleasure of the Bullet!
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mrrstr

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Re: Valve job - better breathing
« Reply #2 on: March 11, 2013, 01:02:04 PM »
Sorry to bring back a dead thread, but I was wondering about doing something like this, and wanted to know: did you have to rejet the carb?  How has it held up over time?

ace.cafe

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Re: Valve job - better breathing
« Reply #3 on: March 11, 2013, 05:10:03 PM »
Sorry to bring back a dead thread, but I was wondering about doing something like this, and wanted to know: did you have to rejet the carb?  How has it held up over time?

You have to first determine what jets are in your carb.
The factory jets that it comes with are mostly too lean, but it is common for them to have been replaced along the way in a used bike.
If you want a jet recommendation, we need to know what air filter system and what exhaust system you have, and what elevation above sea level you are at, and the approximate temperature range at your location. These are the things which affect the jetting the most.
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Chasfield

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Re: Valve job - better breathing
« Reply #4 on: March 11, 2013, 06:23:10 PM »
Bike is still running nicely.

I had already up-jetted the 28mm carb before I did the head work because I am running a free(ish) flowing silencer and a K&N air filter element under the R/H toolbox. The main jet is now a 125 and I think the pilot jet is the #30 but can't remember for sure. I also put in a new carb slide with a one size richer cutaway. That filled up a mid range flat spot quite nicely.

Not sure what would have been required for the head work alone but in any case, I reckon a bog standard 2001 Bullet goes way better with richer jets. The factory shipped their machines out set awfully lean.

As regards ambient conditions: I live in England at sea level. It's nearly always bleeding cold!
« Last Edit: March 11, 2013, 06:28:28 PM by Chasfield »
2001 500 Bullet Deluxe

barenekd

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Re: Valve job - better breathing
« Reply #5 on: March 11, 2013, 08:59:01 PM »
Do a plug check on it. Without doing that you will never be able to get it exactly right. Have a couple of main jets with you a couple of sizes up and down from what you have now. Put a new plug in it when you get to a spot where you can run it wide open for a couple of miles miles. Put the new plug in and run full throttle for a mile or so, then cut off the engine and coast to a stop. Pull the plug and see how it looks. It should be a brownish color. If it's very light, or particularly white, it's too lean. If it's black, it's too rich. Adjust the main jet to suit, and repeat. The rim of the plug should basically match the porcelain. It the rim is light and the plug is black, the plug is too cold, if the rim is black and the tip is white, the plug is too hot. If your running the standard plug for the bike, it should be OK. You can do the same thing at half throttle to check the needle position mixture.
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