Valve clearance adjustment - image

[rigspelt]

I couldn't find an image of the atomic 4 valve clearance technique, which is well described here in other posts, so I made up this. Is it correct? My understanding is that the clearance is maximum, the valve spring is fully relaxed and the valve is closed when the camshaft has rotated to that piston's TDC, and that both intake and exhaust valves at a cylinder are closed at the piston's TDC.

Also attached: the valve clearance adjustment worksheet I made up and Don reviewed a few weeks ago in another post somewhere here.

UPDATE #1: clearer image to show the clearance gap better. The valves are nicely diagrammed in Robert Staton's "Service and Repair Manual for Atomic 4 Marine Engine" (Seacraft Publications, Toronto, Canada).

UPDATE #2: the label "locknut" in the image below is wrong. It isn't a locknut, just the top of the tappet shaped to take a wrench. Hold the tappet with one wrench and twist the adjusting nut with another wrench. Takes some force to move that nut. See rest of thread.

[ne57301]

I'll soon have the same question. Looking at the Tappet picture in Moyers Catalog I'm guessing 'B' but I'm not positive.

[Don Moyer]

Beautiful! Not to beg, but if you could remove just a bit more masking tape to expose the flat spots on top of the tappet, you'd have everything in your photo to illustrate making an adjustment in the clearance.

Don

[Don Moyer]

I'll soon have the same question. Looking at the Tappet picture in Moyer's Catalog I'm guessing 'B' but I'm not positive.

The valve clearance is indeed the space between the top of the tappet and the bottom of the valve stem when that particular cylinder has the piston at the top of its compression (or power) stroke (commonly referred to as TDC). This would be "B" in your photo.

Don

[rigspelt]

I spent a couple of hours practising finding TDC on each of the cylinders and measuring the present clearances.

How critical is it that the crankshaft be turned "to vertical"? Is it allowable to be a few degrees before or after perfect TDC? I found it hard to judge super precisely when the crank pins were vertical.

1. I think the crank pins are vertical on the end of the crankshaft just before the small triangle mark on the flywheel cover, not when the top pin is pointing at it. I think this is because the hole in the center of the flywheel cover does not appear to be centered over the end of the crankshaft. Could that be?

2. I measured the clearances for the I and E valves at cylinder #1 all the way through the #1 intake stroke after I first felt a puff of air in the #1 spark plug hole. I could swear that the clearances were slightly wider just after half way into the stroke than when the pins were vertical. Is this possible? Both valves should be closed during the compression stroke from BDC to TDC, and remain closed during the power stroke from TDC to BDC, right? If so, then would not the clearances on both valves be maximum from BDC through TDC to BDC at that part of the 4-stroke cycle?

3. The next stroke is power, when both valves should be closed anyway, so is it acceptable to err a bit on the side of going a tad too far past TDC?

Here's what I found today:
1E .008 slight drag
1I > .008, < .010
2I > .008, < .010
2E > .008, < .010
3E .008 slight drag
3I .012 slight drag
4I .010 slight drag
4E > .006, < .008

I have not had the nerve yet do what appear to be the necessary adjustments.

[rigspelt]

Here's how I think it works:

The tappet is an intermediary part between the camshaft and the valve.
The valve spring compresses when the cam drives the tappet up into the valve stem base forcing the valve open, and relaxes when the tappet drops down allowing the valve to close. The tappet falls a short distance away from the base of the valve stem (the clearance gap).
Valve clearance is the gap between the valve lifter (tappet) and valve stem, ensuring that the valve closes completely. Clearance too low: valve does not close completely, so engine performance suffers. Clearance too high: valves get hammered.

Compression stroke up, both valves remain closed and compression builds.
TDC: both valves closed, spark plug fires.
Power stroke down, both valves closed.
BDC: both valves closed.
Exhaust stroke up: the exhaust valve opens after BDC and then closes before TDC.
TDC: both valves closed.
Intake stroke down: intake valve opens after TDC and then closes before BDC.
BDC: both valves closed again.

[ne57301]

How's this?

I think this pretty much answers that question!!

Randy

[rigspelt]

Another wrinkle I haven't figured out yet. Just found this in a Universal manual for engines including the A4:

"b. Two types of tappet adjusting screws are used: one is of the self-locking type and the other has a locking nut for holding the adjusting screw in place. Before making the adjustment, this locking nut must be loosened and the adjusting nut held in place when it is retightened after the adjustment is completed."

[rigspelt]

I think this pretty much answers that question!! Randy

Great photos! I'll get better ones when I get back to my boat, which I've moved from the driveway to an indoor shop for the winter. So now I have to drive to the boat.

Looks like we have different adjusting mechanisms on the tappets. I'm still uncertain exactly how to proceed with the wrenches. I wonder if I hold the lower locking nut while turning the adjusting nut? See my last post about there being two styles of tappet locking mechanisms in Universal engines.

[Don Moyer]

I've never done an official "traverse" of valve clearances as you rotate the engine through TDC, but I would expect that the lower radius of the cam lobes have a slight dimensional variation that would explain clearances other than the official specification as you approach TDC from either direction.

As long as you line up the roll pin vertically (it's really one pin that extends through the front of the crankshaft), you should be OK. I've never noticed any variation in valve clearance if you vary a couple degrees from vertical.

Don

[Don Moyer]

Atomic 4 tappets are self-locking. You simply hold the top of the tappet with a 1/2" open-end wrench and turn the threaded part with another open-end wrench. Early engines have 7/16" hex-headed tappet adjustments, and later engines (circa mid-seventies) have 1/2" hex-headed adjustments in the tappets. From your photos, you appear to have the 1/2" variety.

Don

[lat 64]

valve clearance

Hi all,
I think I should weigh in on twothree items here.

A few degrees off of dead center is ok to adjust valves, you are all the way on the back side of the base circle of the cam at this point. Many auto valve-adjusting procedures call for doing more than one at a time, in those cases the cam must be quite a few degrees off of dead enter when they are measured. I would do them one at a time of course, like you are.

There is both a minimum AND a maximum. Stay in the range that is specified for valve clearance (eg. .010 to .012 or whatever.) Too tight can let the valves stay open when the engine gets up to temp and hot gases flow past the valve seat and then the valve starts to burn.
Too loose and it just makes lots of noise and beats up the valve tip. Rigspelt covered this, but it's important.

Also make sure you adjust them at the proper temperature. Some engines, like the old ford 292 v-8, must be at near operating temp for valve adjusting( Yes, it's very painfull. ) Others, mercedes diesel comes to mind, need to be ice cold to get it right. Check the spec.s for A-4.

Finally, it is good practice to practice. Adjusting valves is almost a black art on some engines like the old Datsun L-16 types. On those darn things the lock nut would actually stretch the adjuster screw so it would never be the same thing twice. Get lots of experience for what it feels like to do this on the bench if you can. so when you are laying in dirty oil with a battery terminal poking you in the ribs you can be efficient and accurate adjusting the valves. I always "run the rack" more than once if I can to check my work. there always seems to be one or two that mysteriously get missed or change clearance with just a few turns of the crank

Russ
p.s. Great pics

[rigspelt]

I posted a sketch of how the crank pin, piston position, valve state and distributor rotor position relate to each other during a part of the A4 four stroke cycle here: http://www.moyermarine.com/forums/showthread.php?t=2930

[rigspelt]

Help: Should adjustment nuts be so tight?

I tried adjusting the gap today on the valves. I put a 1/2" wrench on the lower "locking" nut, which spins freely, and a 7/16" wrench on the upper adjusting nut. Should it be so hard to turn that upper nut when holding the lower one fixed? I don't see a way to back off the so-called locking nut, turn the adjusting nut, and retighten the locking nut. Doesn't make sense to me.

My tappets look different from the ones ne57301 shows in his photos in this thread. See a clearer picture of mine below.

[Don Moyer]

You're likely simply not turning the upper nut (at the top of the adjustable part of the assembly) with enough force while holding the top of the tappet. The lower 1/2" wrench position is actually the top of the tappet, not a locking nut, as you're calling it. You can turn the tappet freely with a 1/2" wrench as long as you're not holding the upper nut with a second wrench.

Don