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Author Topic: Hot cylinder head  (Read 1577 times)

David R

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  • Bullet 65, BMW R75/5 Suzuki DR650
Hot cylinder head
« on: February 01, 2008, 12:54:27 AM »
Hi, I just turned 2,000 miles today and my Bullet is running better than ever, but it seems that my cylinder head stays awful hot! I measure it with a  thermometer and It usually over 300 degrees F, just ahead of the plug when I pull back in from a ride. It is down some 25 degrees on average, but my plug comes out white. I have loosened the banjo fittings at idle and they leak oil, but I wonder if enough is getting through. Thoughts, experience anyone?

Vince

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Re: Hot cylinder head
« Reply #1 on: February 01, 2008, 01:17:26 AM »
Keep in mind that combustion temperatures approach 3000 degrees. 300 on the outside is not  that bad. At a stop temperature will spike because there is no cooling air flow over the fins. That being said, you should check carb jetting. Due to differences in bikes, as well as different altitudes, it is hard to be specific. However even with the stock carb and pipe I jet up 3 to 8 stages on the main jet. The jet # can be 117.5 to 130. The pilot jet gets bumped 1 or 2 sizes to 25 or 27.5. But it varies. I sometimes run larger or smaller. The rule of thumb is to jet up until it is too rich, then back down one size. Do one circuit at a time. First main, then pilot. Have a lot of fresh plugs with you. Have fun!

David R

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Re: Hot cylinder head
« Reply #2 on: February 01, 2008, 01:41:26 AM »
Thanx Vince, I just got it running pretty happy. I've only gone up one jet size on the main. (stock exhaust, air cleaner) But perhaps I should try that. I was also wondering about the increased capacity  oil pump that CMW offers. Their catalog claims cooler head temps.

mbevo1

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Re: Hot cylinder head
« Reply #3 on: February 01, 2008, 03:01:00 AM »
David -

Here's my .02 on the hi-cap pumps...

I purchased them with my new '07 Classic.  Took a while before my bike arrived (last shipment of '06).  After reading lots of discussions on the hi-cap pumps, most of the seasoned veterans on the Yahoo RE groups tend to think that they probably don't do a whole lot for an otherwise stock engine.  In fact, at least one of them says the stock pumps "float" at anything above about 3000 rpm because they're pumping more oil than the rest of the system can distribute. 

I ended up not installing them... they're out in my spares box in the original envelope. 

I loosened one of the oil banjos on the head on a warm engine and revved it up... a LOT of oil came out.  I think the stock pumps are working OK...

Mike and Stumpy in Michigan
'07 Classic - Stumpy
'10 C5 Military - Sherman

dogbone

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Re: Hot cylinder head
« Reply #4 on: February 01, 2008, 03:06:47 PM »
Pro : an air cooled engine is partially cooled by the oil, greater flow, cooler running.
Con : the oil pump drive system is a weak link. more volume = more stress on the drive gears.
I would work on Timing,Jetting,Spark plug heat ranges first
99 Enfield Bullet 535
a man isn't drunk,if he can lie on the floor without hanging on

Thumper

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Re: Hot cylinder head
« Reply #5 on: February 01, 2008, 06:40:57 PM »
David,

I'm with Vince. One of the best ways to make an air-cooled engine run cooler is to enrichen the mixture.

If your plug is white, that's a sign of a lean mixture (note that I did not say *overly* lean because it may not be). If there are any blisters on it then it definitely is too lean and hot.

Increasing the main jet would be a good place to start.

Does it ever get hot enough to smell funny?

Does it ever get hot enough to cause performance problems? (missing, stumbling, rough idle)...

As long as you give it adequate and fresh oil and none of the above are true, I'd tend to think you're OK - but making it a bit richer probably won't hurt!

Matt

SRL790

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Re: Hot cylinder head
« Reply #6 on: February 02, 2008, 03:44:56 AM »
Installing a high capacity oil pump on any engine with an "end" fed crankshaft is not always a good idea.  You run the risk of blowing out the oil seal (on the Enfield the cork with a hole in it) and leaving your bottom end with no oil at all!
Andy Wiltshire
54 350 Bullet, 62 Jaguar MK II, 68 BSA Spitfire, 69 BSA Starfire
70 Bonneville, 71 Bonneville, 71 BSA B25T, 74 Jensen Healey
74 Honda XR75, 81 Yamaha MX80, 82 Suzuki GS1100G

fredgold52

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Re: Hot cylinder head
« Reply #7 on: February 02, 2008, 06:43:06 PM »
David, I think it's very good you are being conscious of the heat situation.  Heat is the enemy of any engine.  As Thumper suggested, watch the jetting, both main and pilot, to be sure you don't have a lean running condition.  Also, check your timing to be sure it's on target and your valves to be sure they are not too tight.  All three are pretty easy to do.

When you can pull the plug after a nice long ride and see a chocolate brown color, or coffee with cream if you prefer, you can bet you are set up pretty well.
2006 '65' and a 200cc Stella, Indian all the way