|
|
Posted by Joe Cimoch [68.189.252.175] on Saturday, February 25, 2012 at 18:23:03 :
In Reply to: Valve clerance posted by Alberto Dominguez Sarmiento [186.108.95.21] on Saturday, February 25, 2012 at 13:58:05 :
From the Best of the Forum:
David Goldman Asked:
Many of you must have adjusted the valves on a 251 cu in in a WM300 (66 in my case). I am looking for the definitive methology. I know what the manual says:
.010 Intake (Hot)
.014 Exhaust (Hot)
But hot seems hard - i.e. the manifold is really right in the way.
So - the question stands - What's the best approach?
Hot or Cold?
What should the clearance be?
How to minimize skin loss?
Any special tools?
Gasket set number?
Etc.
I've adjusted a lot of valves, but this will be my first flathead, so I assume there are a few tricks to the trade. Any help or hints would be appreciated.
Thanks in advance.
Alan Bowes wrote:
Try to set them hot if at all possible. Setting them cold will mean having to use a larger gap and not getting consistent results due to differences between the thermal expansion from valve to valve.
Hint: Remove the inner fender panel and the right front wheel to make it easier to get in to adjust the valves. Wear a high-temp sleeve protector so you don't burn yourself on the manifold. Some people use thin gloves, but it's really hard to "finesse" the adjustment with gloves on.
Also, use a thin, flexible valve adjusting wrench that will flex a bit as it moves up and down with the lifter.
If you really have trouble with the moving adjustment, it's possible to warm up the engine, then stop it, quickly rotate the crankshaft so that the lifter for the valve you are adjusting is on the opposite side of the cam from its lobe, and quicky adjust that valve before it cools down. You have to plan ahead and act fast. I'd guess that you should try to adjust the clearance within 30 to 60 seconds after shutting off the engine. Even that isn't foolproof, although it should be pretty close. Warm up the engine thoroughly between adjusting each valve.
Generally speaking, for best accuracy it's best to adjust it while it's running at a slow idle to make sure that the valves stay warm and that they're all a similar temperature. This is kind of a "lost skill" these days and it will take a bit of practice, but it's not really all that hard. You probably already know that the feeler gauge will always be tightly gripped as the cam lobe comes up on the valve lifter/tappet you are adjusting, and you only have a fraction of a second while the lobe is pointing downward to test the clearance.
Gaskets are easy to find at places like VPW or large auto parts stores.
Have fun.
Alan
Steve McManus smcmanus@mis.net posted:
I wonder if anyone out there has the COLD valve settings for the 230 six. I just can't imagine setting them with the engine runnung as described in my old Motor book. Thanks
Alan Bowes wrote:
Subject: Re: Valve lash - Tips for hot adjustments.
I've never been satisfied with cold adjustments. Sometimes they work fairly well, but often not. One problem with setting valves cold is that the expansion characteristics of the valves, etc. can vary between batches of valves, depending on the metallurgy in each batch. It can also depend on things like whether the exhaust stems are sodium filled or not, or whether all of the valves are from the same lot, etc. If you adjust valves while they're hot, you can set them to their minimum safe clearance and still avoid the danger of burning a valve from its being held open as the result of an overly small clearance. If you set the valves when they're cold, you should err on the safe side to avoid too small of a clearance when they're warmed up, which means that a few of the valves will usually end up being kind of noisy, plus you'll be losing some lift, which equates to some loss of power.
IF you follow the procedure in the TM, hot adjustments are a LOT easier to make. The problem is that it's a fair amount of work to prepare for it.
Remove the right front wheel.
Remove the right fender splash shield.
Remove the heat shield for the fuel pump.
Remove the crankcase ventilation line.
Unscrew the crankcase vent metering valve to move it out of the way.
Remove the valve covers.
More work, yes, but now you can get to things a LOT easier. Set valve clearances to .014 inch, hot.
Remember to solidly block and secure the vehicle and don't let any kids play around it while you're doing this, since you'll be working under the fender with the vehicle in neutral and the engine running. This is a true recipe for disaster if someone is goofing off around it.
Have you set tappets before? Setting tappet clearance is a bit of an art, and it requires a rather light touch. As the engine is idling, you should be able to slide the feeler gauge in and out during the part of the cam rotation when the raised lobe of the cam is opposite the point where the tappet contacts the cam (i.e., the raised lobe is pointing straight down). You should feel a tiny bit of drag as you slide the gauge, but not too much.
One thing that helps is to use "tappet wrenches." These are long, thin open-end wrenches that don't interfere with each other as much as thicker ones would while you're making an adjustment. A good set of tappet wrenches is also nicely rounded on the edges so that the bouncing wrenches aren't so hard on your hands. One helpful tip: If you're in a cramped position, don't try to handle two wrenches and the feeler gauge at the same time. Check the clearance, put the gauge down, and make a slight adjustment with the wrenches. Then check the clearance again, etc.
There is also a compromise method that sometimes works pretty well. It involves warming up the engine (with the valve covers off, of course), then stopping the engine and immediately turning the crank to a position where you are sure that the tappet that you are adjusting is against the side of the cam opposite the raised lobe (lobe pointing down). Quickly adjust that tappet while the parts are still hot. Start the engine again and run it for a couple of minutes, then shut it off and repeat the procedure for the next valve, and so on, until you have done all 12. It helps if you put a chalk mark on the lower pulley and figure out the proper crankshaft position for each valve adjustment prior to starting this procedure. Remember that the crankshaft rotates twice as rapidly as the cam, so there's a 50-50 chance that you may have to turn it one extra revolution to properly position the cam. It really isn't as hard as it sounds. I've done this on several engines where access was di!
fficult, and I've never had a noisy (or burned) valve yet.
By the way, if you happen to notice any loose tappet adjusting screws, you may have a problem. You could try replacing an adjusting screw, but often it requires replacement of the tappet to restore the snug fit. I'm not sure if these adjusting screws are available in a special oversize, but I kind of doubt it. If you have to replace a tappet, you might as well pull the engine, as far as I'm concerned. They are normally OK, however.
When you're done, you'll be drenched in oil and sporting a couple of new blisters and battle scars, but you will have survived one of the great adventures in automotive lore: setting tappets. Consider it to be a true nostalgic experience that you can have today without having to pay admission.
I just noticed that I forgot to mention the intake valve clearance. So, here are a few more bits of information:
Exhaust clearance (hot): .014"
Intake clearance (hot): .010"
For the intial setup (cold) clearances when you're assembling an engine, the TM says to use .010" on the intake valves and .015" on the exhaust, but I'd personally suggest using at least .011" for the initial intake clearance and .016" for the initial exhaust clearance, then tweak it when it's hot. (If this were an overhead valve engine, I'd add another one or two thousandths to those initial clearances, since there would be more and longer pieces of steel between the cam and the valve seats, all of which expand when hot.) Alan
Hydraulic lifters? Who needs 'em?
Alan
Patrick Cherry blkburnhse@aol.com Wrote:
Steve, Alan's suggestion re:running the engine to get it hot, stopping, setting one or two valves, running again is probably the easiest way to get an accurate hot setting for your valves. The only way I know of to get a good cold setting is to adjust the valves hot like the book says, then let the engine cool completely (at least 24 hours), then, without starting the engine, rotate it by hand and check what your cold clearances are -- this will give you an idea how each valve should be set if you don't want to continue doing it hot.