Valve Guides: Bronze vs Cast iron?

[Bob S.]

Hello - The '66 L-79 I'm having "restored" already has "bronze valve guides" based on the receipt from a previous rebuild (only about 20,000 miles ago). No other detail on the guides (manufacturer/part number/etc.) was recorded.

I've done a lot of searching on this site and found several opinions expressed that cast iron is more suitable for a street engine. A stock rebuild is planned with as many OE quality parts as possible, and a little spirited driving on completion, but no racing. The ultimate goal is restoration of the original engine so it will be durable if driven another 75,000-100,000 miles and properly maintained.

What are the pros and cons of bronze vs cast iron guides? If the bronze guides are still serviceable (o.k dimensionally with no severe wear), should they be replaced with cast iron guides? ....Or should I stick with the bronze guides since they're already there?

Thanks in advance for your help.

Regards,
Bob S.

[Clem Z.]

Re: Valve Guides: Bronze vs Cast iron?

Hello - The '66 L-79 I'm having "restored" already has "bronze valve guides" based on the receipt from a previous rebuild (only about 20,000 miles ago). No other detail on the guides (manufacturer/part number/etc.) was recorded.

I've done a lot of searching on this site and found several opinions expressed that cast iron is more suitable for a street engine. A stock rebuild is planned with as many OE quality parts as possible, and a little spirited driving on completion, but no racing. The ultimate goal is restoration of the original engine so it will be durable if driven another 75,000-100,000 miles and properly maintained.

What are the pros and cons of bronze vs cast iron guides? If the bronze guides are still serviceable (o.k dimensionally with no severe wear), should they be replaced with cast iron guides? ....Or should I stick with the bronze guides since they're already there?

Thanks in advance for your help.

Regards,
Bob S.

it depends who did the work and what materials they used. bronze wall guides need to be fitted with hard chrome plated valves stems. spiral wound bronze wall guides are the best from the stand point of lubrication BUT need to be equipped with positive type valve stem seals. the bronze wall inserts can be removes and a cast iron sleeve installed

[Bob S.]

Re: Valve Guides: Bronze vs Cast iron?

Thanks Clem. F-M V1756 valves w/chrome stems were fitted and the heads do have "positive seals" (according to the very informal handwritten-on-a-plain-piece-of-notebook-paper "receipt").

The previous owner mentioned a problem after the rebuild (done for the owner before him) and that something had to be repaired, but I don't know exactly what was done.....replace a couple of guides? or seals?

The fact the rebuild lasted little more than 20,000 miles before needing to be redone, doesn't give me a lot of confidence in the workmanship.

I'm leaning towards "starting from scratch" with good/best quality parts all around....I don't want to go thru this more than once.

[Loren L.]

Re: Valve Guides: Bronze vs Cast iron?

I'd almost be that the "something that had to be repaired" was rocker arm stud related - are the studs now threaded or pinned? 40 year old metal...
kinda falls into the category of Why Not put a bolt through the balancer.

[Bob S.]

Re: Valve Guides: Bronze vs Cast iron?

Sorry Loren, I didn't make it very clear. Whatever needed to be redone after the rebuild had to do with the valve guides. I just don't know whether it was guides, seals, or ???

Bob....

[Bob S.]

Clem: Bronze vs Cast iron valve guides?

Clem -

In a previous postings, I've seen you (and others I think) indicate that cast iron guides are better for a street engine than bronze. This makes a lot of sense to me since iron is harder, and should wear at a slower rate (everything else being equal.....) than bronze. Am I seeing this correctly? But this makes me wonder why bronze guides are so popular? Does it have to do with the higher RPM of hi-perf/race engines?

I'm still struggling with the choice of guide materials. It makes sense that iron would be more durable, but a proven valve seal arrangement is limited to the inferior nitrile OE design. (I am thinking more and more about researching a viton circular cross section o-ring that would provide comparable "fill" of the gland between the valve stem and retainer as the OE square section seal.....but am nervous since that would be my own totally unproven "design").

Thanks,
Bob

[Clem Z.]

Re: Valve Guides: Bronze vs Cast iron?

CI guides hold the oil better for valve stem lubrication. the spiral wound bronze wall guides are better than solid wall bronze guides because of the shallow spiral groove that allows the oil to get in to the area but on a street engine that operates in high vacuum conditions a lot this will cause oil burning. i never checked but i think the bronze wall guide material is harder than CI

[Clem Z.]

Re: Valve Guides: Bronze vs Cast iron?

here is a complete write up on bronze wall guide replacement. judge for your self and like i posted before it depends what they used and who did it. http://74.125.47.132/search?q=cache:...lnk&cd=5&gl=us

[Duke W.]

Re: Valve Guides: Bronze vs Cast iron?

The vast majority of auto engines now have aluminum heads,which require some sort of guide liner, and bronze is almost universally used. "Bronze" covers a large family of alloys, and I think nickel bronze is currently the best, but silicon-bronze was used in the past. The same also applies to cast iron - different alloys and grain structures.

In any event one must select a proper system, which includes guide material/design, seal technology, and valve stem surface treatment, and the K-line spiral bronze guide with a positive type viton seal and chrome plated valve stems should be very durable and yield low oil consumption.

BTW, I checked some online catalogs for the OE type seal, and photos clearly show that it's not a common O-ring design. I also failed to find any in Viton, so maybe I am wrong about their availability, but I recall someone mentioning that Viton versions were available.

Duke