OJCar
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"You are Malcolm and I claim my £5"
- Thread starter Robotstar5
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brightspark
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had a pinto head re worked . bronze guides fitted from memory about 125 thou skimmed off it for higher compression hardened valve seats fitted and valves refaced then it got a very light grinding with fine paste by hand so the faces were a mat grey all over making the perfect seal
This was the point @whm_fab was making, in that valve/seat faces shouldn't make full contact.
Typical cutting angles are 45deg for the seat, and 44deg for the valve, so the actual contact area is as narrow as possible.
The larger the contact area, the easier it is for something to stop the valve seating correctly.
A correctly cut valve and seat doesn't need lapping.
Ah, that explains why in all the footage of factory cylinder head production lines I've watched I've never seen a wizened old bloke with massive shoulders sitting at the end with a valve sucker grinding all the valves in . ...
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oldbikedavey
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Nah...."You are Malcolm and I claim my £5"
oldbikedavey
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Don't think that Perfect Seal gasket compound is easily available any more.
Went over to Loctite 5923, and won't be using anything else on paper gasketed joints or crankcase faces.
Old as the hills, but very good indeed.....
brightspark
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we are talking valves not gaskets
the only gasket for the head i use felpro gaskets from burton power products about 57 quidoldbikedavey
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Just down the road from me, but I'll bet they don't do anything for BSA's....we are talking valves not gaskets
keithski122
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In my years I've only ever given a valve a quick lap by hand with coarse paste, never could be bothered with the fine paste lapping. A quick leak test with the fluid from the parts washer and never had any problems with them leaking.
Farside
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Yep, done that too, not had any bad results from doing it slow and steady, avoiding undercut.
Ubique
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I've lost count of the number of M-B M139 / M260 cylinder heads I've changed, all entirely due to the post-combustion injection to give the 'boy racer' exhaust crackle... The M260 heads were supplied fully assembled whereas the M139 were supplied bare with the Magnesium alloy exhaust valves individually packaged in water & fire resistant packaging. The workshop instructions for the assembly of the cylinder head expressly prohibits the 'lapping in' of the inlet or the exhaust valves.
Counter that with my recent place of work where a DW10 engine with low compression due to (mainly) valve leakage - apparently - it wasn't my job... was made worse by excessive 'lapping in' with lashings of fine grinding paste, so much in fact, another tin had to be purchased. None of which really mattered because they chose to re-use several single-use fasteners, including the camshaft & crankshaft pulley bolts ('they've only been used once') - something gave way and some of the newly lapped-in valves were mashed into the pistons on a 'it just needs running in' extended high rev. run after a compression test with poor results....
That is just one reason why it's my 'recent place of work...'
premmington
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I used to have this debate with my Dad... If the head is new and the valves are new and they are the perfect angles - they should not need lapping.
It is when heads have been reconditioned - seats recut - heads should be pressure tested valves/springs/collets in - cams out - valves up.
If you reusing stuff - lapping comes into the game...
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@keithski122 "A quick leak test with the fluid from the parts washer and never had any problems with them leaking."
This is how I do it - drop of Derv in a fairy liquid type bottle. I too always just use course paste.
I hate lapping valves - I got air driven oscillating thing to do it with. But I would also put a wooden type stick thing into battery drill.
brightspark
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hand finish is allways the best 
Try fine..
Well I wouldn't want the inlet valves to be red hot - the exhausts? not that important. Ultimately the valves will just grow, the head and seats will move and deform. But to eliminate what you can makes sense to me, otherwise why bother trying to make your race engine better than anyone else's. You carry on having the shivers, I build race engines to win, not fart about at the back. Sometimes these tricks don't work, but I've never had a catastrophic failure, I have mostly made progress though.
Melvyn Best
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I, on the other hand find lapping valves in by hand to be therapeutic ,except when you can’t get the sucker to hold the valve. I think the first set of valves I ever lapped in were on a Jaguar mk10 which after assembly need shimming , again the first time I ever used a set of feeler gauges ( remember them?) and a micrometer. This was a week or so after my 15th birthday . Unfortunately my arthritic hands would struggle with valve lapping these days
8ob
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I get that but do doubt some of the methods/beliefs some of the race engine builders follow. I get the distortion thing with bolting down a head on a block, in my mind the only way you could check seat distortion on an installed head would be when its torqued down on a block, that would have to be somehow done from the underside with the crank,pistons and rods removed, that would then all change when its up to temperature. Where do you stop? I am also sceptical of the theorised advantages of torque plates on blocks when honing, how does that thick slab they use represent the amount of block distortion a flimsy head with a gasket under it would impose on the same block?
Bob
Well. All this distortion of the block bores is measurable and exists. Making a torque plate to replicate it is a difficult trick, but that doesn't mean don't do it - I've never torqued down a head, tipped a block upside down and measured it, but I think I will, if only to prove or disprove the extent, and difference between a head and a plate.
As I understood it, its more to do with the distortion from the bolts, rather than the actual head. Some engines you can see polishing around the areas where the head bolts are, with honing marks still visible around the rest of the bore.
Heard of some race engine shops using heated oil, using plates with galleries in to circulate the oil to create thermal distortion too. I guess with race engines on the limit, every teeny, tiny, bit helps. But for engines where the head bolts drop into a ladder under the block, so no distortion around the bores . . . ?
I suppose it's a little extra you can charge the customer for.
For one of our highly stressed machines, we do machine with a substitute component bolted up to create the same effect as in use - seems to work, certainly reduced the number of failures/increased service life.
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This is the sort of thing I'm working on
Just got to remember to check for valve seat distortion after dropping it in a bucket of boiling oil
Just got to remember to check for valve seat distortion after dropping it in a bucket of boiling oil
