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Tappet Adjustment - Solid & Hydraulic
 

TT2 should be viewed to determine the best camshaft positioning method for your particular situation. Once you place your cam lobes correctly then you can adjust your tappet clearances. If you have an overhead camshaft (OHC) engine, then the principal is the same. The only difference is there are no pushrods or lifters. The rocker arms make direct contact on the cam instead of a tappet. To make it easier, still look for the valve movement as you would with a pushrod engine to determine the correct position. So with the camshaft now in the correct position lets set the tappet clearance. Choose which one is more suited to your style of engine.

The following is the adjustment of a solid tappet cam follower in a 6cyl Holden engine

The hydraulic lifter positioning and setting is exactly the same as the solid tappet. The only difference is the clearance  is set to zero plus half to three quarters of a turn as shown in the next video.

If set correctly, no further adjustment will be required of the hydraulic lifter supposedly for the remaining life of the engine. In reality though there may be times that you will need to either do them again statically or you might like to adjust them while the engine is running.

The table below shows the relationship of how far the push rod socket is pushed into the lifter at various turns of the nut on a Holden 6cyl engine with a stud & nut set-up for the fulcrum. This is for a 3/8" UNF stud that has a pitch of .041" per thread. If your stud is a different size or thread then you will need to know the pitch to calculate what is required to adjust for one quarter turns of the nut. The formula for a 1:1.5 ratio rocker is calculated by multiplying the nut movement distance by 1.68 as calculated by my CAD program. There is an actual formula on the Hydraulic Lifters article in the engine section.

Turns of fulcrum nut

Fulcrum movement

Lifter plunger movement
1/4 turn

.010"

.016"  (.40 mm)       
3/8 turn

.015"

.025"  (.63 mm)      
1/2 turn

.020"

.034"  (.86mm)      
3/4 turn

.030"

.050"  (1.27 mm)      
1 turn

.041"

.069"   (1.75 mm)    
1 1/4 turn

.051"

.086"  (2.18mm)      
1 1/2 turn

.061"

.102"  (2.59 mm)   
1 3/4 turn

.071"

.119"  (3 mm)   

 The running method is much quicker but can be messy if you don't have rocker stoppers or a tappet cover with the centre cut out to access the rocker post nuts. Both devices pictured below.

If you don't have a cut out tappet cover or rocker stoppers, try using a piece of cardboard to deflect the oil spray. When doing a V8, only do one side at a time. If you have to remove the fuel line to get the cover off, make sure you reconnect the line before starting the engine, otherwise bad things will happen, like a fire.

Start the engine and let it idle. Position the cardboard to control oil spray. Start from the front and loosen the rocker arm pivot nut (anti-clockwise) on the first rocker until it begins to rattle. Stop at this point, then turn the nut clockwise until that particular rattle just disappears. I say just that rattle because you may hear several rattles during the adjustment procedure. This is because the tappet cover acts as a bit of a baffle when fitted, so it quietens down any rocker clatter. Once removed you will hear this clatter but ignore it unless it is a distinct tapping noise, similar to the loose rocker you just loosened. Over tightening will cause that cylinder to miss, if this happens, back the nut off and start again.

Repeat this for every rocker until all are done. You need to do all the rockers quickly, because as I said it can get very messy. If you have the oil under control you can slow down a bit and take your time. Tip- don't be smart and undo all the rocker nuts at the start thinking you can save some time. It makes it very difficult to know when the rattle is gone when all the others are rattling loudly.

When done, STOP the engine.

Check the thread pitch of the rocker post. If it is a fine thread then tighten every rocker nut a further 3/4 turn. You will find that this will be the most common. If the pitch is coarse like a whitworth or UNC then only do the nut up a further 1/2 turn. That's it. Do not start the engine at this point. Replace the rocker cover after cleaning any mess that you made. Re-check that you have assembled everything correctly. The engine should now start and be rattle free.

Also don't be too concerned about making the engine lifter rattles totally quiet. You will notice that when I adjust the lifters running in the video that some sound like they are loose and they probably are. The aim is to get one to rattle louder than the other and then tighten it to make the rattle disappear. The minor rattles won't disappear until you turn the nut down a further half to one turn, I prefer 3/4 of a turn. The tappet cover also acts as a deadener as said before so you will not hear any rattles if the lifters are adjusted correctly. The following video is fairly old, back in the early days of filming. I do plan on replacing it when another opportunity comes.

After the adjustment, if the lifters still rattle then you have a problem that needs further looking into. Check all the rocker components from springs back to the lifter or possibly a worn cam lobe.