Auto Technologies Head swap frustration
- Thread starter aries
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I was hoping he was gone. Maybe he could turn his own negative comment and say when the flag drops the ignorance stops. :roll:
Hi Chaps!
Thanks for your responses thus far. Changing jet size has made no difference to the problem. If I lower the choke it falters readily. so its not running lean. But I shall tinker on.
Fuel is via the H configuration of pipes from tank. I keep both taps on and as metioned, never had problem before with the original combat head.
Certainly it has more poke at low and mid range speeds, sounds more throaty too. However when patience runs out I may just refurbish the original head and stick it back on the bike, leaks and all!! Crazy eh.
Cheers
Aries
Thanks for your responses thus far. Changing jet size has made no difference to the problem. If I lower the choke it falters readily. so its not running lean. But I shall tinker on.
Fuel is via the H configuration of pipes from tank. I keep both taps on and as metioned, never had problem before with the original combat head.
Certainly it has more poke at low and mid range speeds, sounds more throaty too. However when patience runs out I may just refurbish the original head and stick it back on the bike, leaks and all!! Crazy eh.
Cheers
Aries
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Hi , I cannot imagine that a simple head swap could kill speed to such an amount , should be something else somewhere, but what ? that being said , if you are fed with your fullautohead you can swap for any of mine : combat , RH5 or STd ..... :roll:
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I don't see where you say you contacted fullauto for suggestions? He is on this forum and I imagine he'd be interested in helping solving your set up problem.
Could that copper head gasket be leaking between the cylinders under higher-load conditions? Seventy mph is about what my Combat will pull with a dead cylinder. If it'll run on one cylinder I'd try revving it with a compression tester in each hole to see if the dynamic BMEP is above 130 psi or so.
Tim Kraakevik
kraakevik@voyager.net
Three Commandos
Tim Kraakevik
kraakevik@voyager.net
Three Commandos
aries
take it out and run it up in 1st ,2nd and third and tell us what it does. if it does it at the same RPM in all gears you are probably looking at a valve float issue. what you will than have to do is remove the head and compare the measurement from the valve spring seat to the valve retainer on both heads. you will probably find that the distance is greater on the new head and you will want to set it to the original head spec.
take it out and run it up in 1st ,2nd and third and tell us what it does. if it does it at the same RPM in all gears you are probably looking at a valve float issue. what you will than have to do is remove the head and compare the measurement from the valve spring seat to the valve retainer on both heads. you will probably find that the distance is greater on the new head and you will want to set it to the original head spec.
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aries said:
Aries, the head is designed after a standard head. The combat heads were machined differently in the spring seat area and did not use fiber washers under the intake spring seats. Some of them used spring seats that were a different thickness also.
You would want to check the valve spring installed height on your cylinder head and make sure it is close to the recommended height as specified by the spring supplier.
If you do not have fiber washers under the intake spring seats then I will almost guarantee that the intake springs are not compressed enough. If you have thin spring seats then you may need two fiber washers under the exhaust seat and one under the intake seat. The best bet is to measure the installed height of your springs and go from there. Jim
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Educational on spring height issues. I think I've experienced valve float trying to pass a semi during my first days on a Combat, it sounded horrible misfiring as power dropped till I up shifted just in time. Could one really have valve float w/o some nasty symptoms besides dull power top out?
Jim. Thanks for your input. Im being qiute dense here, but how can I measure the spring height. The spring seat is one fixed point, but where do I go from there?
Perhaps I could compare the seating height between the two heads, but with such potentially small measurements that doesnt sound very accurate I know!
Thanks again
Aries
Perhaps I could compare the seating height between the two heads, but with such potentially small measurements that doesnt sound very accurate I know!
Thanks again
Aries
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Seems an awful lot of complicated answers in relation to a problem which may well be very simple, and easily solved with 1 hour dyno set up session.
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Aries,
Do all the simple stupid tests first you shouldn't start pulling it to bits until you've exhausted all of them;
A compression check will ensure there's not a head leak and the valves are closing, check the ignition is advancing, perhaps you've upset the wiring and its not, what do the plugs look like? try a new set, etc.
Best of luck mate.
Cash
Do all the simple stupid tests first you shouldn't start pulling it to bits until you've exhausted all of them;
A compression check will ensure there's not a head leak and the valves are closing, check the ignition is advancing, perhaps you've upset the wiring and its not, what do the plugs look like? try a new set, etc.
Best of luck mate.
Cash
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aries said:
You can get a close enough measurement of the valve spring installed height to know if it is the problem by using a 6mm wide strip cut from a tin can about 4 inches in length. The object is to find out exactly how long the spring is when it is in place on the head with the valve fully closed.
Slide the strip down along side the valve spring so the end of the strip is resting in the lower spring seat. Now take your pocket knife and make a small cut in the side of the strip at the point where the top of the spring meets the upper spring retainer. Now remove the strip and measure the distance with a good rule or caliper. Or compare the reading with the old head if they are using the same valve springs.
If the measurement is within 1.5 mm of the spec then this is not likely to be the problem although for maximum performance this measurement should be within .5 MM of the spec. Micrometers are available that replace the spring temporarily to measure this height. Jim
Thanks for your ideas chaps. Played around and checked a few things today, but not taken bike out yet. Having tried most other things to no avail I do suspect the possibility of the valve springs lacking compression. Pain in the arse, but something else to go on.
The old Norton never ceases to surprise, cure one problem and discover another, but its all worth it when they do run well,eh. Thank goodness for this forum.
Cheers All
Aries
The old Norton never ceases to surprise, cure one problem and discover another, but its all worth it when they do run well,eh. Thank goodness for this forum.
Cheers All
Aries
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