Automotive valve guides 660 bronze instead of cast iron
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  1. #1
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    Default Automotive valve guides 660 bronze instead of cast iron

    Good morning All:
    This is a question for all you automotive guys.
    I've been asked to make replacement valve guides for a customer who apparently makes and runs antique race cars.
    The original guides are cast iron (based on what he's told me...I have no idea what motor this is going into)
    He wants replacements in 660 bronze.

    He gave me a sample (a "good" one) from the ones he pressed out of the head and I'm supposed to make the new ones "the same" as the old.

    Here are my questions:
    Do I make the press fit for the bit that goes into the head the same as it was (0.7515" ) which assumes a press fit of 0.0015" if the bores in the head are nominal 3/4" diameter.
    Do I bore to +0.002" clearance for the valve stems as per the sample, assuming the bores will collapse when the guides are pressed in and can simply be honed back to size after fitting.
    Can 660 bronze be easily honed with the standard tools you'd use in this application or is this going to be miserable to do?

    I'm a bit concerned about the consequences of just making and putting these new guides in without thinking this through first.
    I ask because the coefficient of thermal expansion for 660 bronze is almost double that for cast iron...with too hefty a press fit, is there a risk of cracking the head when it all gets hot?
    Is there a risk of the bushing collapsing onto the valve stem and making the valves stick?
    The customer can't answer any of these questions and the mechanic downstairs (I'm directly above an auto restorer) won't stick his neck out so I'm kind of just going with the best consensus I can get here.
    I was hoping one of you would have specific experience to point me to any pitfalls.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Well my experience was with air cooled MC's but does the valve guide have a lube supply? Did a old 40s Norton at customer insistence with bronze and it Stuck! Engine in question relied on oily vapor coming up push rod tubes .Fail! Cast iron lived just fine. Being your engine is likely water cooled expansion of the bronze likely not a issue ,lube is however. In most automotive engine rebuilding/repair I've been around guide finishing is done by reaming.

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    The way I remember from my hot rod days was the guide was bored and the sleeve inserted in that. A little extra clearance is good. The guides were rather thin. Check with a couple hot rot shops or older engine builders.

    Ed.

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    Would not use 660....for valve guides unless this going into an open valve gear style engine T or F head (no splash oil on the top)...
    For oil lubed valve gear think the 660 is too soft.
    Would rather go with Ampco 45, or 642 bronze.

    Don't need heavy press. install guides and finish ream with guide reamer (piloted end start) to clearance.
    Lots of old stuff has flanges on the guide for the springs to sit on that keep the guide in place...
    Lots of "Monoblock" cylinder/head setups (Miller. Alfa, Bugatti) require the guide to be removed to install the valve.....Light push fit here is the rule.

    In general,(not a hard rule) Bronze guides seem to have a greater tendency to stick than cast iron....Got to give them enough clearance.
    Cheers Ross

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    IME (admittedly limited) bronze valve guides are made from a harder ''Alu Bronze'' type rather than the softer lead bearing,

    X2 on ensuring the correct clearance, some engines (notably early Perkins diesels) are sods for sticking valves if the guides aren't reamed to the right size.

    As for the expansion rate difference - IMO the CI will have a higher hoop strength than the bronze, so I'd stay with about the same ''nip''

    Oh, and warm the head to fit the new guides.

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    Quote Originally Posted by JohnEvans View Post
    Well my experience was with air cooled MC's but does the valve guide have a lube supply? Did a old 40s Norton at customer insistence with bronze and it Stuck! Engine in question relied on oily vapor coming up push rod tubes .Fail! Cast iron lived just fine. Being your engine is likely water cooled expansion of the bronze likely not a issue ,lube is however. In most automotive engine rebuilding/repair I've been around guide finishing is done by reaming.
    Reaming after installation should be standard procedure. Apparently the guides will shrink a bit in their fit after being pressed in. I used to work on Harley-Davidson cylinder heads and there was a hand reamer tool that was used for this purpose.

    I believe cast iron valve guides are superior to bronze but my only experience is with motorcycle engines.

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    Fabrication job, or an engineering job? If the first then have the customer provide a dimensioned print, and manufacture
    to that print. If it goes sideways then its on him.

    If an engineering job then charge accordingly.

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    Do not use 660. You want to use SAB (silicon/aluminum/bronze). Press should be .001" and guide to valve running clearance should be .0015". Warm the head before pressing. Normally valve to guide running clearance is automatically established by using a purpose made valve guide reamer. I don't know why you are doing this. This job is quite quickly done on a special valve guide machine like the Italian Serti. I'm sure most automotive machine shops have at least one. Further new SAB guides are available over the counter in all kinds of different sizes. Don't reinvent the wheel.

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    I've seen this literally hundreds of times in my 41 years in the automotive machining business. Bronze guides in a cast iron head will stick a valve if not clearanced properly. And by properly, I mean rigid honed under constant oil bath, not reamed. Unless you have a task specific carbide bronze valve guide reamer ($175 each), a regular reamer will not do the job. The guide will not be straight or round. Typically twice the clearance of a cast guide is correct.
    Bronze guide in an aluminum head does not have the sticking issue. .0015" press fit is correct. Installing with liquid nitrogen is the easiest but heating the head will work also.

    Also, bore them .0015" over stem diameter and let the installing machinist do the final sizing with his rigid hone setup, hopefully. FYI, Serdi is French and they are nothing special other than using a live pilot system that is fast, but with that speed comes inaccuracy with the wrong operator. I've seen seat runout as much as .015" done on one of those machines.
    Last edited by slowmotion; 12-09-2019 at 02:52 PM. Reason: added more

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    Hi again All:
    So the customer was sent to me because he originally had some made by another shop and apparently they were so far off center that the valve seats could not be cleaned up.
    To the best of my understanding he could not buy what he needs from the store, for whatever reason
    The guys below me (RX Autoworks) suggested he come and see me.

    Problem is I don't know this turf well at all so I'm shooting entirely in the dark here.
    I know I can make the bore and the body concentric with one another; and I can hit the dimensions he wants, but he doesn't seem to be able to tell me definitively..."here, make THIS" with a picture and dimensions and material specs.

    So I have a 1" dia bronze bar cut up in pieces sitting on my floor...it's 660 bronze per our telephone consensus, and from all of you who've commented, it's the wrong material and opens a whole new can of worms I didn't anticipate.
    My gut tells me to call a screeching halt to the whole sorry enterprise right now until this can be sorted properly.

    So I'm looking at a new bar; either Durabar or 642 bronze per Alfa GTA's recommendation (thank's Alfa...I owe you one!).
    I'm looking at letting him know the experiences some of you guys have had with bronze guides in cast iron heads and I'm looking for a decision from him, not me on what he thinks will work.
    I'm clearly not competent to make these judgments, and I ain't gettin' paid to do so, so I ain't gonna!

    To all who responded to this thread' thank you very much...it's appreciated!

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    Last edited by implmex; 12-09-2019 at 06:45 PM.

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    In general ,bronze guides were used in alloy heads ,so that the guide would stay put when the aircooled head got hot.....JAP used steel guides with a bronze liner ,only on inlet valves ,exhaust guides were always cast iron......Another point is that exposed exhaust guides wont work with an oil scraper ring on the piston......not enough lubrication.

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    not knowing the valve stem dia but possibly an easy way would be to make the cast guides to od then bore to accept off the shelf guides from such places as goodson.com

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    More than likely, the original guide was not concentric i.d. to o.d. and that's why the seats did not align when concentric guides were installed. For this reason I started installing guide liners in the original guides some 20 years ago. This way you do not lose the original guide centerline and valve seats line up. Most all heads manufactured today have non concentric guides. Guides are installed in the head with unfinished i.d.'s (usually .015" small), then the guide is bored and the seat is machined in one setup. Works great but the guide i.d. and o.d. are not parallel, but it doesn't matter until the guide is changed. You may want to punt on this project and tell the customer to call PEP, they will make custom guides in the proper intake or exhaust material as needed.

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    The OP may be trying to make something that is readily available at $10 for a packet of 12......Rule #1.....never get auto parts made by a general engineer....waste of time and money.........its quite likely the counter girl at the local engine reconditioner will be able to recognize the guide and supply a replacement for under a buck a piece.....and whats more with a correctly honed bore and a centreless ground OD,accurate to tenths.

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    I would propose fixing it like this:Bronze-Liners & Tooling | Goodson Tools & Supplies

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    Quote Originally Posted by john.k View Post
    In general ,bronze guides were used in alloy heads ,so that the guide would stay put when the aircooled head got hot.....JAP used steel guides with a bronze liner ,only on inlet valves ,exhaust guides were always cast iron......Another point is that exposed exhaust guides wont work with an oil scraper ring on the piston......not enough lubrication.
    IIRC air-o-plane recip engines (continental, Lycoming, franklin) used a bronze
    of some sort.

    Recall the head (the whole jug) was heated in an oven, and then a piloted
    driver was used to push them home.

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    I never liked bronze guides, sticky, and so much clearance to keep them free, they pass too much oil. Cast iron is much better. And do it all in one setup on a seat and guide machine. Ive heard if guys doing them in a mill, have not seen it done that way. You need the head, or block as the case may be, and the valves. Fast, concentric, and it wont come back. Good luck with any other methods.

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    OK, some further information:
    In reference to your post #13, slowmotion, I checked the one old sample guide I have with a gauge pin and a clock, and it's concentric to better than 0.001".
    So may I assume the others will be too?
    This was the "good" guide...all of them were pounded or pressed out of the head with a punch, and are apparently not salvageable.

    With respect to your post #14, john.k, I am given to understand these cannot be bought and need to be custom made...I do not know why but I assume it's true.

    So all notions of sleeving them or salvaging them in some other way or just going to the store appear to be off the table.

    I've sent an email asking for more guidance...man is this ever turning out to be a lot of admin.
    The programming and proveout literally took less time than the correspondence and internet research.
    BTW, for the poster who asked, the stem diameter is 0.375".
    Also, for those who've alluded to me doing the install and fitting; I am only supposed to make 16 guides and deliver them to him...he will be doing everything else so once it leaves my shop, it's no longer mine to deal with.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Would you care to state the ID/OD/L/Flange position of the guides.....or the motor they are out of ,if known,

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    At a previous shop we never made guides out of Ampco 45 but we made a lot of guides out of Ampco 18. From what I know about Ampco materials, 45 is favored where the bushing may run out of lube and seizing is very undesirable.


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