Q&A / Tech

Mailbag: Tips for Changing Valve Seals Without Removing the Cylinder Heads

Q: I’m changing the valve seals on my 1973 Camaro. The cylinder heads are on the engine, and the engine is in the car. I’m using compressed air to hold the valves closed. Also, the Camaro has an automatic transmission. How do I keep the engine from rotating?

A: This can be done by using an engine-rotating tool and a breaker bar. Attach the rotating tool to the harmonic balancer. Next, attach the breaker bar to the tool, and rest the bar’s handle against a rigid surface in the engine bay. Depending on the crankshaft position, the engine may rotate in either direction when you pressurize the cylinder. Apply compressed air slowly, making sure the engine is rotating in the desired direction. If not, re-position the breaker bar as necessary, keeping it clear of wiring, hoses, and delicate components.

This is another in a series of weekly Q&A Mailbag sessions with Summit Racing‘s tech department, in which there are hundreds more. Click here to see them all

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6 Comments

  1. Jeff Pitman says:

    There is alot more to this than whats here is the rest of the answer somewhere else?

  2. I used to just stick a length of cotton clothes line in a cylinder and rotate the engine till it jammed the valves in their seats. Foolproof method. Change springs and seals without an air compressor in the pits.

    • That’s the craziest thing I ever heard but it sounds totally feasible and better than the compressed air methods. My only question is how do u convert cotton clothes line to a fluid measurements of CC? To long of a line stuffed in there could cause damage or compress it to the point of of pushing it into the piston ring gap. It would be like putting a tampon in there with a pull string hanging out of the spark plug hole. Lol! I give this method a careful thumbs up !

      • Alan Donaldson says:

        It’s an old tried and true method. Except I heard it with nylon rope so you don’t get any pieces or rope in your cylinder. It works just fine,you can’t compress it enough to squeeze it into the rings.

  3. Michael wilson says:

    I imagine that if you are changing valve seals, you would be changing them all and would have removed all the rockers. At that point it would seem unnecessary to require the engine not to rotate. The cylinder you are working on would just be forced to bdc and stay until you changed to the next cylin

  4. I am currently using the clothesline trick to free stuck intake valves on a vehicle that was in storage for over a decade. I use a flywheel wrench to turn the motor over, load a cylinder with about three feet of line, then slowly turn it over by hand until it stops. I can then remove the valve springs and seals. I cut a funnel to fit tightly around the valve guide and fill it with penetrating oil and wait. After a few days the valve comes free and moves easily again. I reinstall the seal and valve spring, and move on to the next one. This engine has head studs on it, so the alternative is pulling the motor. I’m happy to wait this out.

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