Grinding valves

[DW]

I've taken the engine to bits following a leakdown test which showed that I was getting leakage out of the 2nd cylinder intake, plus small leakage past the rings in all cylinders.

 

How do you re-grind valves? Is it just a matter of using the paste as an abrasive between the valve and its seat to grind a match?

 

 

 

David

1700XF

[PAUL MARRIOTT]

And a lot of elbow grease 😬

 

DVA's method is to place the valves in their seats, switch the lights off (you'll need darkness to do this) get a good torch and shine it on the valves whilst peeping throw the ports, move the torch round to various angles, if you can see light through the seats grind some more. Give the Head, Seats and valves a good clean first so that the muck doesn't block the light.

 

I would do all the valves while you have it stripped.

 

Paul M

[DW]

Bought a spring compressor (G-type) but can't get the springs to compress - presume I'm doing something wrong! I've put the fork bit over the top of the caps, and screwed the bottom of the compressor up to the valve underneath. There's an arm on the G Clamp that compresses it further and locks, but I don't get any movement on the springs to free the collets........

[DW]

Aha! Light blow with the hammer does it

[PAUL MARRIOTT]

Ping......there goes another 5 mins looking for the damn things on the floor

[thinfourth]

Never done this on a car engine but done it on other valves.

 

You should have a sucky thing to stick on the valve and use it to turn it.

 

You want a backwards and forwards action so rubbing it between hands works.

 

Some lapping/grinding paste is a bit dry so a touch of oil will thin it down a bit and give you a slightly better action. Clean it up regualrly and look a nice even grey ring once you have cleaned it off.

 

Another check is to get a marker pen or even better engineers blue and so round one of the mating surfaces and give the valve a light spin and it will show any high spots.

 

 

O/T time for big valves the seat and valve are ground at different angles so when the valve heats up the angles close up and you get a better seal.

 

Sod the heater wheres my shades

[owelly]

I have spent many many hours franticly rubbing, getting callouses on the palms of my hands, but thats a different story......

After you think you have ground the valves in, drop a little paraffin/similar round the seat and see if it leaks away to the valve stem/port. If it does, keep grinding ☹️

 

its only a game.........

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[oilyhands]

The best test to see if the valve is properly lapped is to clean the seat in the head completely clear of all traces of paste, preferably with carb cleaner or similar, dont use excessive amounts or it will wash paste down the guide, clean it with some rag / workshop wipe moistened with cleaner. Then wipe the seat of the valve clean lightly with a *dry* wipe / rag, this leaves just a trace of paste on the seat of the valve. Put the valve in the guide and close it, turn the valve two complete revolutions and remove. If you dont have a grey line of paste deposited all round the seat in the head in an unbroken line then the valve isnt lapped. If you do, chemically clean the seat in the head again and repeat. If the test suceeds again, the seat is lapped. Clean valve and seat and do the light test described above.

 

When lapping ensure the rubber sucker sticks properly to the valve head and is concentric, place your hands as far as possible towards the top of the stick and cup your thumbs over the top to stop them slipping down. Do not use excessive pressure or excessive paste. As well as the reciprocating motion, lift the valve off the seat a little every 3-4 seconds to redistribute the paste back into the seat. DO NOT let any traces of paste enter the valve guide. Sometimes a cable tie around the rubber at the business end will prevent the wooden stick slipping in the rubber end. Occasionally I have placed the end of the stick in an electric drill for more troublesome seats, on a slow speed this can break the back of the lapping provided you finish by hand, just don't lean the valve is any particular plane while lapping.

 

It's not uncommon for the collets to lock in the cap, someimes so much that you can bend the spring compressor. To slacken the grip of the collets on the cap (and not loose them), a sharp tap on the cap with a suitably sized socket and short extension will normally do the trick, if the collets fly out they will be contained by the socket...

 

Oily

[Paul D Jones]

The best test to see if the valve is properly lapped

 

Is to use Oily's method but use engineers blue you only need a spot the size of a pin head and rotate the valve 370 deg anymore and you could be covering up little imperfections in the lapping

 

After you have finished wash the head and all components grinding paste CAN cause a valve to stick in the valve guide with all the cost that goes with a bent valve

 

Paul.

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