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valve lapping: necessary or not?

instrument for valve repair
according to the manufacturer statement
the valve lapping after is not needed.

mr tuomo kurki-suonio runs experiment
in finland after he has taken the engine
from the service station after the repair.

after being treated with
special instrument, the vacuum test
has shown 50% valve leaking.

lapping paste from vmpauto

after the valve treatment by classic lapping paste,
vacuum tester has shown just 10% leaking.

on the original rolls-royce engines
the bronze fixing is used for the soft valve work

antifriction paste fabo, vmpauto.
after fabo treatment
the thin bronze
layer is formed on the valve.
after fabo treatment
the containment level is 100%

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     valve lapping: necessary or not?
still about 40 years ago, regular valve lapping was necessary to keep the engines running. today many of the modern ice (internal combustion engines) do not need anymore valve lapping as a part of the regular maintenance. but when the time comes to repair the engine, then the valve lapping is needed or not?

     the engine repair shops, which are machining the internal parts of the engines, do not anymore lap the valves after they are handled by the machine tool. the reason is, they say, that the surface of the valves is good enough to be air tight, so anything more is not needed.

     sometimes however, some car or motorcycle owners do have realized that just after the engine as been assembled, it has been a little difficult to start and the idling has been erratic. those who have the possibility to use a high quality exhaust gas analyzer have been able to see that the value of the hc, the unburned hydrocarbon, is very high, much more what it should be in a repaired engine.

     but is it necessary to be so, to waste the expensive fuel for saving the extra job of the valve lapping?

     as the lapping paste manufacturer vmpauto, st.- petersburg is producing high quality lapping pastes with several different grades, we decided to test and see what the difference is.

     the engine was an opel 2-liter 8-valve, but technically the requirements are always same for four stroke engines of all makes and independent of the engine design. more there are valves, more it is important that they are air tight.

     by bare eyes the machined valves look good. we decided anyway test the tightness with low capacity electric vacuum pump which is normally used in the test bench to test the vacuum capsules of the distributors.

     the cylinder head has arrived from the machine shop as ready to be assembled so we just turned it upside down and dropped one valve on its seat. then we connected our vacuum pump with conical rubber piece to the intake channel of this cylinder.

     big was our surprise as the pump was showing almost 50 % of the leakage! from the experience we knew that this leakage will become less after the engine has been assembled and been running a while, but now we could see the actual reason for the bad running of the repaired engines assembled without valve lapping or not doing it correctly.

     the next step was to lap the valve with quality lapping paste. in this test we used the classic lapping paste from vmpauto. its quality has been proved by 100 000 times in many years, when it has been supplied to the mechanics, to workshops and to car accessories shops. in 3 minutes the surface was looking much better. now there was a grey line all around the valve head.

     back to the test bench to see if this short job has corrected everything. really, the result was excellent, the leakage being only 10 %. that is the point where most engine repairers will stop. it is good enough. but is it really, isn't there still something to do?

     the old mechanics do know the method of the "knocking" the valves. that is hitting the valve against its seat to get the opposite surfaces a bit smoother. to get the full benefit of this practice there is available from vmpauto a material called anf, antifrictional nonabrasive finishing. this treatment is giving a bronze film of 2 - 3 mu thick on the surfaces of the valve and its seat.

     quite a lot of effort is needed to get the correct finish with anf. it is necessary to press the valve with 5-10 kg force and the complete treatment for each valve will take 5 - 10 minutes. so we did and after that the sealing surface of the valve has bright bronze color.

     to see if this extra job was worth of it we dropped the valve on its seat and connected the vacuum pump once more. now we could understand why rolls-royce has chosen this finishing method for their engines. in our test the valve was 100 % tight!

     of course all the valves of this engine were handled with similar way. and after that we did the same also in the next engine. in fact we decided never to be satisfied with standard methods as much better way is available at almost no extra cost.

     we strongly recommend every car mechanic to do the valve lapping job correctly. now you can have the choice of several different grades of the valve lapping pastes made by vmpauto. just choose the best and do the rest!

     p.s. the engine in the example was for an historic racing opel kadett rallye. this car has been winning now in two races against the cars like a factory bmw 2002 and fuel injected ford escort bda, so maybe there is some magic at the valve lapping with best possible products.

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