Valve guide work

[camelotr]

Hi,

Recently I had all my cylinder heads done by machine workshops. As my knowledge is slowly rising (from zero to nearly nothing :-) ), I have realized, that "mass production" work is not always the best for my beloved old cars. Now I would like to learn the basics of cylinder head reconditioning. This wont make me an "expert", but at least will enable me to check the works, and correct them if necessary.

First I would like to ask some help around the valve guides.

My recent cylinder head is a Mini 12G940 casting, with "fastroad" modifications: slightly ported cambers, 3 angle valve seats, 35.6mm inlets and 31mm rimflow exhausts (each has chrom stems) and I plan to "round" the top side of the intake valve to better flow.
.
As advised by the "pros", I have bought bronze valve guides (manganese). They were fitted by the machine workshop.

How to adjust the clearance? What numbers to go for? I asume bronze guides need bigger clearances than cast iron, am I right?

Why are bronze guides better than cast iron?

[stevieturbo]

Only way to adjust tolerances is to ream the guide out once installed.

As to what those clearances need to be...havent a clue.

And Bronze offers better heat conduction to remove heat from the valves ( at least exhaust valve anyway )
I'd guess it is also a better self lubricating material than cast iron ? it is just a guess though.

[Pumaracing]

camelotr said:

As advised by the "pros", I have bought bronze valve guides (manganese). They were fitted by the machine workshop.

How to adjust the clearance? What numbers to go for? I asume bronze guides need bigger clearances than cast iron, am I right?

Why are bronze guides better than cast iron?

In general they aren't. I never use them unless they are fitted as standard with no other option. Cast iron lasts much longer. For some strange reason people think bronze guides are fashionable and they must have them in their engines.

Standard clearances will be fine. 0.02mm inlet, a bit more on the exhaust say 0.025 to 0.03mm. Adjustable reamers such as Taylor and Jones are the best choice for reaming guides. Don't even think about buying cheap Chinese adjustable reamers which will either not cut at all or just break their blades however J&L Industrial in the UK do their own Value brand with HSS blades which work as well as T&J ones and are a lot less money, like 1/10th the price.

http://www.mscjlindustrial.co.uk/CGI/INPDFF?PMCTLG...

Manganese bronze can refer to a number of alloys but the most common in the UK is material code CZ114. It's basically just a fairly soft high tensile brass not really a proper bronze and won't last as long as cast iron guides. It's used because it's cheap and easy to machine - not because it's a good valve guide material which it certainly isn't. Aluminium bronze, code CA104 is a "proper" valve guide material. Tough as old boots and a right barsteward to machine but twice the cost of CZ114 so no one ever uses it.

Edited by Pumaracing on Sunday 27th February 12:56

[camelotr]

Hi Steve, Pumaracing,

Thanks for he introduction.

Some people tell me to use bronze valve uid with stainless steel valve stems and cast iron with chrom. Does it have any reason to do soo?

May I ask You to tell me an acceptable way to measure the guide-valve stem clearance?

[Pumaracing]

camelotr said:

Hi Steve, Pumaracing,

Thanks for he introduction.

Some people tell me to use bronze valve uid with stainless steel valve stems and cast iron with chrom. Does it have any reason to do soo?

May I ask You to tell me an acceptable way to measure the guide-valve stem clearance?

Whether the valves are stainless steel or not the stems should still be chrome plated or tuftrided and if not you shouldn't be using them.

I thought we covered stem/guide clearance measuring in some detail in the last thread?

http://www.pumaracing.co.uk/bronze.htm

[ian_uk1975]

camelotr said:

May I ask You to tell me an acceptable way to measure the guide-valve stem clearance?

Set-up a dial indicator mounted in a stand against the valve margin with the head of the valve as close to the seat as possible. Wiggle the valve and record the measurement shown on the dial indicator. Half that figure and that will give you a pretty accurate figure for valve stem to guide clearance. A potentially more accurate way would be to use a telescoping bore gauge in conjunction with an external micrometer, but in inexperienced hands, the dial indicator wiggle method is easier to get right. A seasoned pro can tell just from wiggling the valve stem if the clearance is acceptable, or not.

[Pumaracing]

As I thought we covered valve to guide clearance measurement in detail here including the formula for measuring stem rock with a dial gauge.

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[camelotr]

Yes we have disscussed the formuly, I just thought it would be good to have it in this opic as well for all of us green novices.

Although since our last discussion over the subject, I have bought an inside bore gauge. Is it a better way? How to use it properly?

[camelotr]

Pumaracing said:

http://www.pumaracing.co.uk/bronze.htm

Very good article!

[Pumaracing]

Article now rewritten, expanded and with links to bronze technical specs.

[Pumaracing]

ian_uk1975 said:

Set-up a dial indicator mounted in a stand against the valve margin with the head of the valve as close to the seat as possible. Wiggle the valve and record the measurement shown on the dial indicator. Half that figure and that will give you a pretty accurate figure for valve stem to guide clearance.

No it won't except in a very particular combination of circumstances. The equation for turning valve rock into stem clearance depends on the lengths involved and has been given in a post I refer to above.