When I've rebuilt a cylinder head in the past I've always lapped the valves in using paste and the sucker on a stick spun between the palms
until a continuous grey line appears on the valve seating face etc. This has always been on either leaded Pinto or A Series heads. We're now
rebuilding a ST170 engine and head. The head is stripped with valves out and wire brushed clean. The head has valve seat inserts (possibly only on
exhaust ports though, can't recall and haven't got the head at moment to check) and both inlet and exhaust valves look good. Is there any
value in lapping the valves in on the ST170 head.
Thanks
Ian
A light lapping with some fine paste will be a good idea, and will show up any abnormalities with the valve seating.
Check the valve guides for wear while it's apart, my zetec needed new exhaust guides when i had the head ported with 80k on the donor car and 25k
in my striker.
Dave
I would at least give them a light lapping in and then check with engineers blue
Put some petrol into the ports with valves in place,if it leaks out you know they need lapping in
Thanks
[Edited on 20/3/19 by Barksavon]
will need so little work to do and insure a really good seal, why not do it. Then pour some petrol in with the head inverted and check nothing drains away over an hour or so
Petrol is really thin and will probably leak out after an hour. I thought paraffin or diesel was the way to go?
Nope should be gas tight which is a lot thinner than a liquid
quote:
Originally posted by Mr Whippy
Nope should be gas tight which is a lot thinner than a liquid
Yeah I get that, but petrol sat for an hour vs a gas compressed for milliseconds, I reckon you could get petrol leaking still but be air tight for milliseconds. I'd turn the head on it's side, fill the ports with your chosen liquid, then blast the valves with compressed air. See if you get bubbles.
quote:
Originally posted by joneh
Yeah I get that, but petrol sat for an hour vs a gas compressed for milliseconds, I reckon you could get petrol leaking still but be air tight for milliseconds. I'd turn the head on it's side, fill the ports with your chosen liquid, then blast the valves with compressed air. See if you get bubbles.
Using engineers blue takes all of 5 seconds for each valve, quicker , safer and more efficient than using petrol and cheaper , a tin lasts years.
You will get bubbles that way, if you get any pressure in the port - because it will attempt to lift the valve slightly. That's not the normal
operating process for the valve, which gets gas pressure ramming it shut.
The default method has always been petrol, that I know of, and I would expect a tiny seep through if at all. If it drains a noticable volume,
it's gubbed.
But ultimately it takes sod all time to lap the valves so why not just do it for assurance?
quote:
Originally posted by coyoteboy
You will get bubbles that way, if you get any pressure in the port - because it will attempt to lift the valve slightly. That's not the normal operating process for the valve, which gets gas pressure ramming it shut.
The default method has always been petrol, that I know of, and I would expect a tiny seep through if at all. If it drains a noticable volume, it's gubbed.
But ultimately it takes sod all time to lap the valves so why not just do it for assurance?
as above pressuring the ports is applying pressure to the opposite side of the valve and more testing how strong the valve springs are than the valve
seats
[Edited on 22/3/19 by Mr Whippy]
quote:
Originally posted by Mr Whippy
as above pressuring the ports is applying pressure to the opposite side of the valve and more testing how strong the valve springs are than the valve seats
[Edited on 22/3/19 by Mr Whippy]