Valve seats

[pasbogdan]

After changing valve guides,valves angle is slightly different and valves do not seal on seats.(i mean i can see light on about 0.5-0.8 mm with valve closed)I never got in this situation with no engine.Will rework seats but i noticed producer says that guides should be replaced only if the distance from end of valve to the botom part of the camshafts holder in no less than 36mm.For the hydr tapet to work.If not they say to renew the head.Easy,no?What do you think about that?If reworking seats to get them perpendicular again on valve axle will get the valve much more uppwards and getting low number than 36 will do what?Throw the head?Did you tryed to rework the end of the valve?I saw that as a procedure for adjusting tapets clearance(they are not hydraulic,also no shim adjustable) on 1.9 diesel renault engines.I think 1.5 dci also.
What do you think?

[JP]

Cut valves cut seats make them seal and then take a little of top of valves for correct lifter clearance. Measure b4 and after and take distance and put this value shim as extra under spring seat to maintain correct seat spring pressure.

When changing guides you will always recut seats.

[pasbogdan]

Thx for answer.I cut seats when i replace guides but never got so much off angle to be forced to cut so much.And audi knows this happens.

[JP]

Only reason you go of angle is if head is not hot enough when fitting guides and you have to ream the guides out to size.

[pasbogdan]

Reaming is necessary,but not on all 20 guides.Some of them do not get under 7mm.
And the ones that do not get undersized in pressing process,when inserting cutting tool for seats with perfect 7mm tale you can see tool contacts only half the circumference of the seat.I guess they get a little off angle(guides) because head does not support guide on his full lenght,but on one side it is shorter.
How do you get the head hot?Using a gas torch local on the guide area or getting into a hot liquid?

[twenty valve]

I made a metal tank, filled it with boiling water and then brought it back to the boil on the hob Attached handles to the head first though so you can pull it out easily.

Also put the valve guides in the freezer the night before. I made a special drift which stepped from 10 to 6.9mm, with an m6 thread on the bottom, so you can slip the guide onto the drift, spin the nut on and hammer it in (quick!) They where all still tight going in though. Probably took 3 or 4 whacks with a lump hammer!

I used an expandable reamer and a honing tool to achieve the right sliding fit for the valves. Every guide required working.

When I re-cut the seats some where quite far out.

[JP]

Heat gun down the port pointed at where the guide goes. Leave it on max for ten min or so till you can't touch the head anymore without burning yourself use a correctly shaped drift and tap them lightly in. No reaming required using febi guides 99% of the time you can lap the valves in without even cutting the seats if doing a stock recon and there is no pitting or bowing on the seats.

[pasbogdan]

Afte milling new hoders for cutting tools to be exactly as the guide got after riming and hold the cutting tool perfect allign i cuted seats.To get the tool to cut to full 360 circle i had to remove a lot from seat on one side.Now from calculations i have to remove 0.8 from valve end.It seems to much.Valve has only one groove for holder and it is about 3mm from top of valve.It will get 2.2 after cuting the end of the valve.I am afraid not to lose the holders for valve as they will be so close to end of valve.I was thinking of removing the interior of the tappet and reface that.

[JP]

Yes you can machine interior of tappet too.