11 replies to this topic

[Udo]

I've refurbed my head after head gasket went including

New valve guides
Cleaned up valves
Reamed the guides to fit the valves
Re-cut the valve seats
Lapped the valves in

Cant think I've missed anything

but the started car up ran for about twenty mins quite happliy then an exhaust valve stuck open

Anybody any idea what would cause this?

Valve isnt bent if you hold it against a start edge but the end has been swollen by the rocker hitting it

[cowboy]

could be a faulty valve. you baught.

i had a problem in canada, put all new valves in a Car for Snshine, a few miles down the road it started to tap,. took the head of after being recovered to find on of the valve heads had fallen off. total right of of the engine, head and pistons all damaged.

hope it hasn't done any damage to anything else.

[Bungle]

were the new guides reamed out after fitting ?

[icklemini]

were the new guides reamed out after fitting ?

indeed - the guides need reaming out once pressed in.. - Though you say they were reamed - Sure this was done right?? (if the machine shop did it then send it back to them!)

TTFN,
Dave

Edited by icklemini, 11 February 2007 - 10:53 PM.

[Udo]

Not new valves and the valve head hasnt detached its self

Guides were reamed out, and I did them so I'm confident it was done right.

[icklemini]

Not new valves and the valve head hasnt detached its self

Guides were reamed out, and I did them so I'm confident it was done right.

what clearance did you allow between the valve stem and the guide?
guide/valve material mismatch?
Bent valve?
Overheating?

[Udo]

what clearance did you allow between the valve stem and the guide?
Didnt have internal micrometer so did them by feel and they all felt the same and would drop thru the guides by their own weight - not brilliant I know but I've done it that way before

guide/valve material mismatch?
Not according to Keith Calvers articles

Bent valve?
Well it wasn't but it is now after close checking!

Overheating?
No

Edited by Udo, 12 February 2007 - 08:04 PM.

[icklemini]

what clearance did you allow between the valve stem and the guide?
Didnt have internal micrometer so did them by feel and they all felt the same and would drop thru the guides by their own weight - not brilliant I know but I've done it that way before

0.0015" clearance on the stem diameter is the absolute minimum
usually a 9/32" ream or a 7.14mm with new valves

guide/valve material mismatch?
Not according to Keith Calvers articles

Iron guides - chrome stems
Manganese-bronze guides - well anything really, but the nitrocarburised ones wear better...

I have come across it before - I put it down to the oil seal being a bit too enthusastic - there was a seal on the exhaust valve, not normally needed as oil dont flow 'down' them stems to burn.. :\ did you put seals on the exhaust valves??

TTFN,
Dave

Edited by icklemini, 13 February 2007 - 12:57 AM.

[Udo]

You may have come up with a reason there as I did put seals on all the stems but then again they are on the inlets as standard and dont usually make them stick.

Also if you look at the mini expert mag it shows KCalver putting his uprated seals on all valves so now i'm confused

Cheers

[dklawson]

A thread has been running parallel to this one where the poster was asking about why there were only 4 valve stem seals in his gasket kit. I made the point expressed above that particularly on newly rebuilt heads you probably don't want exhaust seals.

As mentioned, 0.0015" clearance should be your target. Internal mics may be of some use but the way I check small bore holes like this is with "plug gauges". Basically they are precision ground rods with tightly controlled diameters. Most machine shops have them for inspection purposes.

In-spite-of what KC may have said, read up on valve guide material and valve stem material. There are small differences in the coefficients of thermal expansion and this may dictate minor changes in the "cold" tolerance you apply to the reamed guide diameter you choose.

[fikus01]

i think lawson is onto something, forgot all about heat expansion, look at the valve when it comes out and see if it was 1 spot that caught (dirt/grit) or if its scuffed all round like its been clamped!!

[icklemini]

i think lawson is onto something, forgot all about heat expansion, look at the valve when it comes out and see if it was 1 spot that caught (dirt/grit) or if its scuffed all round like its been clamped!!

exhaust does run hotter than inlet..

exhaust valve has nothing but hot gas going over it.. inlet has a nice cool inlet charge cooling it.

are on the inlets as standard and dont usually make them stick.

inlets dont get as hot.

exhaust valves dont need the seals as any #spare# oil that gets down the guide is blown back up the next time the exhaust valve opens (all that gas coming out of the chanber)

the inlet valve, however, when open has a 'suck' act upon it, pulling air into the chamber, and without seals, oil will be drawn down the guide because of the vacuum...

i only put seals on inlets to be honest..
ttfn,
Dave