Britbike forum

Cast iron guides - advantages?

Posted By: Tigernuts

Cast iron guides - advantages? - 06/15/19 2:38 pm

The late T140s were fitted with cast iron guides for some reason. Does anyone know the reason? I'm guessing it was purely a cost saving measure but maybe there was some supposed advantage?
Posted By: kommando

Re: Cast iron guides - advantages? - 06/15/19 2:48 pm

Self lubricating from the carbon, same principle as machine slideways.
Posted By: triton thrasher

Re: Cast iron guides - advantages? - 06/15/19 4:30 pm

Cast iron guides have always lasted longer than phosphor bronze on my bikes.
Posted By: HawaiianTiger

Re: Cast iron guides - advantages? - 06/15/19 6:40 pm

Old Keith Moore would swear that iron guides last forever. I went with bronze because that's more easily available on most motors.
I find the advantages are that, at least for me, I don't have to buy 5 or six guides because the iron ones break so easily.
But on the other hand, you can knock the iron guides in or out of a cold iron head easily. My bike currently has iron guides. One of them was broken, so I knocked out one from a spare head and installed it in my good head. No problem. Maybe apples and oranges using iron guides in alloy heads. I've never done that.
Cheers,
Bill
Posted By: triton thrasher

Re: Cast iron guides - advantages? - 06/15/19 6:49 pm

The brittle nature of iron guides is why bronze became universal on racers. A bent valve from over-revving would make pieces of cast iron fall into the cylinder and make a terrible mess. Bronze is more pliable.

Of course, if racers used bronze, then the self-styled fast road boys had to as well!
Posted By: Tigernuts

Re: Cast iron guides - advantages? - 06/15/19 9:21 pm

Looks OK then. I was wondering about the difference in rate of thermal expansion, iron being lower than aluminium whereas Colsibro is very close. But if nobody on here is aware of there having been problems with iron guides being prone to coming loose in aluminium heads, I won't worry about it!
Posted By: triton thrasher

Re: Cast iron guides - advantages? - 06/15/19 9:49 pm

There’s a recommended interference fit.
Posted By: NickL

Re: Cast iron guides - advantages? - 06/15/19 11:14 pm

Aluminium bronze, which is the preferred type to use as a valve guide material, has
a much greater ability to conduct heat away from the valve. It is also extremely hard
wearing. Phosphor bronze is easier to finish and size but will not last as well.
Posted By: Excalibur

Re: Cast iron guides - advantages? - 06/16/19 1:38 am

Did Triumph ever spec phosphor bronze as valve guide material? I recall aluminum bronze or Hidural 5 spec'd. Have I remembered wrongly?
Posted By: Rohan

Re: Cast iron guides - advantages? - 06/16/19 2:07 am

Cast iron guides will happily run with little to no oil, but about everything else HAS to have oil.

Are the valve stems chrome plated, that comes into the equation too.
Posted By: Tigernuts

Re: Cast iron guides - advantages? - 06/16/19 9:03 am

They can be chrome plated or not. What's the rule, in iron guides? Chrome good or not?
Posted By: Tigernuts

Re: Cast iron guides - advantages? - 06/16/19 9:08 am

So, iron for inlet OK, but Hidural / Colsibro for exhaust would be a good combination?

I'm looking into this because I've just bought a head which has new iron guides. It just seems odd that Triumph made the decision to change - after god knows how many years - to iron guides, and I wonder whether there were any sound technical reasons for this (or whether there really aren't, and it was purely a cost saving measure). It can have whatever valves I choose (G&S have chrome plated stems, not sure what other choice there is in the UK for decent quality valves?)
Posted By: tridentt150v

Re: Cast iron guides - advantages? - 06/16/19 9:59 am

Every time I have used cast iron guides they have grabbed a valve, usually it was a very hot day if that is any excuse.....I only use phospur bronze or derivatives of it in my bikes. I think the cast iron ones are ok for slow revving low speed old singles and farm machinery, but not for long sustained high [ish] speed rides.
Posted By: Hillbilly bike

Re: Cast iron guides - advantages? - 06/16/19 10:49 am

Originally Posted by Tigernuts
They can be chrome plated or not. What's the rule, in iron guides? Chrome good or not?


Some say with cast iron guides you need chromed stems or nitrided to prevent galling...As Nick says, some types of bronze are better at transferring heat..Powdered metal is now the choice for many newer engines....
Non concentric valve seats are often a cause of valves "grabbing"..Even some shops with expereince can't do good valve work...The best guides and valves won't be worth a crap unless the machine work is dead on...
Posted By: triton thrasher

Re: Cast iron guides - advantages? - 06/16/19 11:17 am

Originally Posted by tridentt150v
Every time I have used cast iron guides they have grabbed a valve, usually it was a very hot day if that is any excuse.....I only use phospur bronze or derivatives of it in my bikes. I think the cast iron ones are ok for slow revving low speed old singles and farm machinery, but not for long sustained high [ish] speed rides.


The “excuse” for valve stems picking up is insufficient clearance.

I’m sure there are better materials than iron now, but it can be a question of who is selling what, to fit what old wreck.
Posted By: Tigernuts

Re: Cast iron guides - advantages? - 06/16/19 10:19 pm

This makes sense. But it leads to the question of what is sufficient clearance? Let's suppose good quality chrome-stem G&S valves in (presumably) decent quality Triumph iron guides - what clearances would be considered the minimum acceptable? (inlet and exhaust)?
Posted By: NickL

Re: Cast iron guides - advantages? - 06/16/19 11:02 pm

The manual will probably spec the clearance, but 1-1.5 I/L 2-2.5 EX is a common 'go to'.
Posted By: Hillbilly bike

Re: Cast iron guides - advantages? - 06/17/19 12:44 am

My T140 street bike and the two race bikes are .001" on intakes and .0015"... These tight clearances only work when the valve to seat runout is practicaly nil...As in done on a single axis valve machine, like a Newan or maybe a Serdi...Or the few real fussy machinists that can hold such clearances with convetional valve facing equipment...
Posted By: HawaiianTiger

Re: Cast iron guides - advantages? - 06/17/19 1:20 am

When I sent my '62 6T head to a specialist, he decided to install Ampco 45 guides and seals , 7mm Kibblewhite Black diamond valves with titanium retainers. He set the clearances at 3/4 thou for inlet and 1 thou for exhaust. I was mortified. I just knew I was going to seize a valve. It worked fine. But, this guy does F1 and other race engines.....just saying. The guy doing the work will know what he can get away with, I would think.
Cheers
Bill
Posted By: NickL

Re: Cast iron guides - advantages? - 06/17/19 7:35 am

On most of these old crates, they will be around 5 thou in a year or two.
Posted By: Stein Roger

Re: Cast iron guides - advantages? - 06/17/19 7:51 am

Norton used cast iron valve guides on all heads I've worked on. They seem to last better than Triumph bronze alloy ones, but then there are other differences as well.
Triumph used cast iron in the TR6 heads, they are longer than the bronze ones, and wear much better. There's little difference between a TR6 and a T120 in power output so I would use cast iron in a T120 without a worry. The longer inlet guide may rob a horse or two in the short run, but this will even out as the bronze guides wear.
A few thousand miles down the road the advantage will be with the iron guides.
IMHO of course.
Posted By: Hillbilly bike

Re: Cast iron guides - advantages? - 06/17/19 9:51 am

Originally Posted by NickL
On most of these old crates, they will be around 5 thou in a year or two.


By 10,000 miles for sure....but like being young and handsome, enjoy it while you can...
Posted By: tridentt150v

Re: Cast iron guides - advantages? - 06/17/19 12:36 pm

Originally Posted by Stein Roger
Norton used cast iron valve guides on all heads I've worked on. They seem to last better than Triumph bronze alloy ones, but then there are other differences as well.
Triumph used cast iron in the TR6 heads, they are longer than the bronze ones, and wear much better. There's little difference between a TR6 and a T120 in power output so I would use cast iron in a T120 without a worry. The longer inlet guide may rob a horse or two in the short run, but this will even out as the bronze guides wear.
A few thousand miles down the road the advantage will be with the iron guides.
IMHO of course.

Yes Norton did use cast iron, and I've also had mates [3 I can think of] on Nortons with valves that have grabbed...…….I am yet to see a +'70's British twin [they were never used on triples AFAIK] with cast iron guides that hasn't had issues. Every one I know of has been converted to PB.

If they work for you then power to you, but everyone I know uses bronze.
Posted By: Irish Swede

Re: Cast iron guides - advantages? - 06/17/19 12:37 pm

The idea of "punching out" the old guides always bothers me. Sooner or later the head will be worn or damaged from this process, and good heads are getting scarcer.

I had the original iron guides bored and threaded for "bronze-wall" inserts.
Those are threaded in, like heli-coils, then reamed to size.

When the insert wears out, you just pull it out and thread in a new one, ream it, and the process begins again.

The insert also holds oil to lube the valve stems, because of it's coils.
Posted By: Tigernuts

Re: Cast iron guides - advantages? - 06/17/19 5:55 pm

Originally Posted by Irish Swede
The idea of "punching out" the old guides always bothers me. Sooner or later the head will be worn or damaged from this process, and good heads are getting scarcer.

I had the original iron guides bored and threaded for "bronze-wall" inserts.
Those are threaded in, like heli-coils, then reamed to size.

When the insert wears out, you just pull it out and thread in a new one, ream it, and the process begins again.

The insert also holds oil to lube the valve stems, because of it's coils.



Is this the same as the K-liner system? Sounds like a good idea to me, but its hard to find shops that know about it, and do it, in this country.

My queries about cast iron guides have been rendered academic now anyway - the head arrived today and they are bronze - the photos on ebay made it look as if they were iron, but it was just 37 years of grime & dust that made them grey, and the seller didn't say.

I've offered up an exhaust valve from my old head and it sticks within about half an inch in both exhaust guides, so either the guides will need honing or I'll have to get some correctly sized valves. The G&S valves seem to come oversize, ie: .311" stem diameter instead of .310 max. This is the case not only with the old valves (no wear on the stems at all after 13000-odd miles) and the new ones I bought (also G&S). On the old ones, the wear to the tops of the stems was negligible - a visible polished stripe where the rocker adjuster pin has been contacting but you can't feel the wear, and I'd guess it at well under a thou.

The fit of the exhaust valves in the guides was the best I've ever found in any used British engine - a lovely sliding fit with barely a trace of 'rock when anywhere from just open to fully open. Wish I could remember what guides I used! They look like Wassell guides but can't be (I wouldn't have used them).

The inlets, on the other hand were a tad sloppy on the drive side to significantly sloppy on the timing side. Not as bad as I'd have expected at 130000-ish miles, but not good enough to re-use. The inlet stems were correctly sized too, and showed about half a thou of wear.
© 2020 Britbike forum