r75/5 I have the heads and cylinders from both sides parted and removed for the pushrod seal replacement. The valves have not been removed. What is the best way to go about cleaning them and checking for proper seating? There is a fair amount of combustion crud on the back side of the valves inside the ports. Any advice or input would be appreciated. Thanks in advance.
• With the valves and springs still in place, you can pour 2oz of liquid (thinner, alcohol, water) into the port. The valve should seal the liquid from entering the combustion chamber for at least 3 seconds.
• You can remove the valves and use a wire brush mounted on a bench grinder to clean off any burned-on oil deposits. It is not necessary for them to be "spotless" or to polish the valve faces. The valves should be re-installed in the port they came from.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
It helps very much. Thank you.
• You can remove the valves and use a wire brush mounted on a bench grinder to clean off any burned-on oil deposits. It is not necessary for them to be "spotless" or to polish the valve faces. The valves should be re-installed in the port they came from.
► You'll want the Intake valve to be fairly clean on both sides. Typically, the fuels with cleaners will have done a good job of this. But there's no need to get them cleaner or brighter than what a wire brush can do.
And the same goes for the Intake port. You don't want any build-up from burned-on oil blocking the port.
You will also want to make sure the screw-in inlet spigot ("Connector") is secure. Those need to be tight in the head to prevent an Intake air leak. If the spigot is found loose, I typically remove them and add a gasket sealer to the threads before re-installing and tightening the spigot.
► The Exhaust valve is another case entirely. It is handling super-hot gasses, and you really don't want those high temps being absorbed by the valve and staying in the cyl head. Since the baked-on carbon is an insulator, I don't typically clean anything off the Ex valves on the combustion chamber side. On the stem-side of the Ex valve, I will remove any burned-on oil deposits that might impede the gas flow. This under-side of the valve is one location where there can be large deposits. I do not clean the Exhaust port.
The Ex port threads should always be protected, and copper-based Never-Seeze should be used when re-fitting the finned exhaust pipe holding "Nut".
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thank you Mr. Whatley for the detail on this. I am considering trying to do the valve service myself and am processing how the components should look like under normal engine operation and your input has been helpful, as a newbie and eager to learn.
The bike has been dormant for some time. Both exhaust valve faces on the combustion side look like dry rust with zero flaking. The seats sweated a wee bit with the leak test after 3 or 4 seconds. I removed all 4 valves. The seating shows a consistent witness ring of rub contact on both the valve and the valve seats on all but the R/S exhaust valve. It had no slack at the rocker. It nor its seat appear to be burnt, but lack the shiny bare metal contact ring like the others.
I welcome any opinion on whether it is worthwhile to service the valves or replace them.
Best regards,Dave
► Combustion happens in a fraction of a second. So if it held liquid-tight for anything near 3 seconds, then you are fine.
► However, it won't hurt to use some very fine Valve Lapping Compound on each valve face. Apply a very small amount onto each valve seat, and then reinstall the valve. Alternate then between 1. turning back-and-forth 15°, and then 2. lifting the valve to rotate 45° into a new position and repeating. The video shows the motion. Only 20-45 seconds is required on each valve.
This guy uses a lapping stick and Pushes. For me, using a 6" piece of tubing from the other side and Pulling is better. Your choice. The object is the back-and-forth motion. For this reason I do not use a drill motor.
https://www.youtube.com/watch?v=pVp04atZoc0
The object is to get a thin, light gray wear pattern all the way around both the seat and valve. Then you MUST remove all the Lapping Compound from all the parts. The compound is carbide paste and it will chew your engine to pieces if it gets into the engine oil. Removing the compound takes longer than the Lapping !
► Obviously, the valves MUST remain matched to the seats. Marking with a Sharpie Marker can help.
Have fun and learn !
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thanks for the tips. The link to the lapping procedure was also very helpful.
Best regards,Dave
@wobbly I am curious why you pull rather than push when you lapp the valve to the seat.
@wobbly I am curious why you pull rather than push when you lap the valve to the seat.
Because Push only works with the suction cup if the valve face is 1. clean enough and the rubber cup is 2. new enough to get a good suction. Whereas any old piece of rubber hose will slip over the stem of the valve well enough to Pull.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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