Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
I found the snug fit dummy valve the best check of absolute concentricity.
I have dismantled several high mileage Minx heads and found porous castings with extensive pits in exh seats yet seemed OK. Obviously must occupy little width. If just due rust probably not deep.
For the BMC A guide clearance is given as .0015 and .002 min, and as modern valves are all one dia reaming might not be necessary esp for inlets.
I find new fixed reamers cut aggressively; one source suggested lubricating and this moderated the cut and gave very high finish.
I wonder what seats are like when the head is tightened and engine flat out hot!
Joined: Aug 2017 Posts: 1,666 Threads: 46
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Location: Auckland NZ
Car type: 36 Nippy, 31 RM, 38 Special, 24 Works Rep
A burnt seat caused by failure to remove past pitting will cause far more damage, I have had to deal with a few AUSTIN 7 engines in recent years with this malady. My belief, rightly or wrongly, is that with little used cars ( and all of these were little used or recently recommissioned without the benefit of a valve grind I should add ) the valves sit open for extended periods, rust forms on the exposed seats, when the engine is run this rust effects the valve sealing properly and burnt seats result. Now Auckland has at certain times of the year quite high relative humidity, so it may not be such an issue in other places, but certainly something worth thinking about. The engines I am discussing in every case had not completed a high mileage since the last valve grind, certainly far less than one would normally consider necessary. I should also add that the cars effected, when used, were only taken out on relatively short runs and I believe this is another factor, how many times have you gone on an long run 150 miles or more with some decent constant speed sections to find the car is running better than ever. My thoughts are that a decent hammering of the seats, provided they are not too bad to start with settles them back in as well as possibly removing some build up.
Black Art Enthusiast
Joined: Aug 2017 Posts: 521 Threads: 82
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Location: Deepest darkest Kent
Good work Stephen,
I use a diamond plated valve for cleaning up burnt seats. With a little paraffin it cleans up the seat in no time. Five to ten minutes for four exhaust seats
Joined: Aug 2017 Posts: 1,808 Threads: 99
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Well done so far, that's some lovely work on making the tooling. You have skills.
It looks like you have some juddering on the cutting surface from having so few cutting heads?
A seat cutter will have around 20 cutting heads.
Also A pickervant kit usually gives you a grinding head, it may be worth buying one of these on its own to grind back the judder.
Also Austins recomendations is the seat head should be no more then 2mm.
The pickervant set usually gives you two cutting angles, one for the seat. And one to cut the excess at another angle.
Hope this helps, Tony.
Joined: Aug 2017 Posts: 312 Threads: 9
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Location: TINOPAI NZ
Hi Stephen,
Just make two sets of cutters to fit in your holder one 30 degrees and one 60 degrees this will allow you to cut the inside and out side of the seat to get the right width on the valve and central on the valve face.
Hope that helps
Colin NZ
Joined: Aug 2017 Posts: 521 Threads: 82
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Location: Deepest darkest Kent
Jeff,
I had a refaced valve diamond plated twenty years ago by a man who made diamond plated files that I use.
I'll see if he is still in business,
Robert.
