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Author: Subject: Grinding in of valves?
Barksavon

posted on 20/3/19 at 06:18 PM Reply With Quote
Grinding in of valves?

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

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obfripper

posted on 20/3/19 at 07:04 PM Reply With Quote
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

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rusty nuts

posted on 20/3/19 at 08:11 PM Reply With Quote
I would at least give them a light lapping in and then check with engineers blue
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CosKev3

posted on 20/3/19 at 10:11 PM Reply With Quote
Put some petrol into the ports with valves in place,if it leaks out you know they need lapping in
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Barksavon

posted on 20/3/19 at 10:32 PM Reply With Quote
Thanks

[Edited on 20/3/19 by Barksavon]

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Mr Whippy

posted on 21/3/19 at 07:07 AM Reply With Quote
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
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joneh

posted on 21/3/19 at 08:17 AM Reply With Quote
Petrol is really thin and will probably leak out after an hour. I thought paraffin or diesel was the way to go?
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Mr Whippy

posted on 21/3/19 at 02:00 PM Reply With Quote
Nope should be gas tight which is a lot thinner than a liquid
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nick205

posted on 21/3/19 at 02:47 PM Reply With Quote
quote:
Originally posted by Mr Whippy
Nope should be gas tight which is a lot thinner than a liquid



I'd agree and gas under a 10:1 compresion ratio as well.

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joneh

posted on 21/3/19 at 05:19 PM Reply With Quote
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.
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CosKev3

posted on 21/3/19 at 05:27 PM Reply With Quote
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.


That won't work,unless you make up an enclosure around the valve that's sealed otherwise the compressed air will just take the easiest route,which will be bouncing off the valve/head!

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rusty nuts

posted on 21/3/19 at 05:31 PM Reply With Quote
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.
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coyoteboy

posted on 21/3/19 at 05:31 PM Reply With Quote
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?





Report your local potholes, it actually works!

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joneh

posted on 21/3/19 at 06:04 PM Reply With Quote
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?


I agree, should be done, and I've just finished doing mine. Just interested in the test methods. The compressed air method seems to be used a lot by others and gives a good indication immediately.

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Mr Whippy

posted on 22/3/19 at 01:00 PM Reply With Quote
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]

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joneh

posted on 22/3/19 at 02:48 PM Reply With Quote
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]


I meant squirting the air around the valve, not in the port. You see the bubble raise up in the ports.

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