Tech Tips: Fall 1994

Bronze Valve Guides

We have enjoyed owning a 1959 MGA 1500 fixed head coupe for more than 30 years. We have been able to keep the car in good condition during that time, thanks to an adequate supply of parts from Moss Motors.

I recently had the valves ground, and had the old steel valve guides replaced with new brass valve guides. After assembly, and when test driving the cat, the engine began to “flutter”. The problem was discovered to be a stuck valve and bent push rod. After replacement of the push rod, yet another valve stuck, although this time the push rod did not bend!

Apparently after the engine is up to normal operating temperature the brass guides expand more than would a steel guide. The solution is to slightly hone the guide when installing. Hopefully this information will prevent someone tearing down the engine of their MG, a second time for valve guide replacement!

-Ken Schutt, Winnegabo, MN

 Camshaft Lifters

I wish to follow up on the Tech Tip #84 which appeared in the Spring issue of “Moss Motoring”. This described how to install a camshaft without removing the head. While this may seem a good way to save labor and a few bills, in actuality you will probably end up spending even more in the long run. Allow me to explain.

Every camshaft manufacturer, and any mechanic worth his salt will tell you, never, NEVER! use old, used lifters, with a new camshaft! Even lifters that look good can cause damage, and usually that will not take long. The reason, and it has nothing to do with selling more lifters, (cam followers, or tappets), it has nothing to do with the bores they fit in, but has everything to do with the “face” of the lifter. In fact the number one cause of new camshaft failure is the use of “old” lifters!

Normal lifter faces arc not flat as most people assume, there is, in fact a slight crown, usually around two thousands of an inch. This in combination with the way the camshaft is positioned in the block relative to the cam, forces the lifter to rotate while lifting instead of just “pushing” the lifter upwards.

If you look down the bores of the lifters with the camshaft installed, you will see that the cam lobes are slightly off to one side of their respective bores. These factors are designed so that the cam lobe and the lifter will mate with each other after a period of break in. This break in is critical to the longevity of the camshaft and related parts and is usually around 30-45 minutes at 2000 RPM or above.

It is not uncommon for a seemingly good lifter to utterly destroy a camshaft within the first few minutes of operation, no matter how much Moly-lube you use! Also, you should keep all the related valve train components identified as to their corresponding place in the block or head.

This results in a mated assembly. If you’re extremely lucky you might get by using “used” lifters, but is it worth the gamble?! Take the extra time and do it right. It might cost a little more effort and a few extra dollars, but the added peace of mind that the job was done without compromise is well worth the effort.

– Barry Schwartz, La Mesa, CA.

…and further support for Barry comes from Frank Ieraci of New York…

How could you recommend replacing a camshaft without replacing the tappets? That has always been a no-no in the automotive world as I know it. The bottom of the tappets become worn in to match the corresponding camshaft lobe, and substituting a new cam would cause uneven wear and premature failure of both parts. Your Tech-Tip section has educated me out of a jam or two in the past and I though I would try and help with this one.

By the way I enjoyed your recent article on “Double Declutch” techniques, I have always been in the dark about this and you really set me straight. Thanks!

-Frank

(Well both readers are right, and it was an error which we shouldn’t have allowed to slip through! Thanks to Barry & Frank and others who wrote pointing out the error. -Ed)

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