Valve guides for exposed valves

[bevanclark]

Hi folks,
Apologies this is a non-Ariel topic, but i feel sure there are experts on this forum who will know the answers to these questions.

I have a 1929 BSA Sloper with exposed valve gear and very worn cast iron valve guides. Valves themselves have very little wear. The head is cast iron and the seats are in good condition. My questions are:
1. What is the correct grade/specification for the grey cast iron which should be used to make new guides ?
2. With such an elderly and relatively breakable head, what would be a "safe" interference fit for the guides ?
3. What valve stem to guide clearances would be appropriate. Obviously, there is no worry about oil going down the stems .

Mnay thanks,
Bevan

[cmfalco]

I used G2 cast iron to make the guides for my 1928 Ariel, sized for an interference fit of 0.002" in the cast-iron head, with 0.002" clearance for the inlet valve and 0.0025" for the exhaust. After 3500 miles, the inlet guide was unworn at a measured level of 0.0001". Unfortunately, the case-hardening on the exhaust rocker wore through, resulting in side thrust on the exhaust valve, so I don't know how the guide would have fared absent that problem.

Ni-Resist 201 Type 1 should be even better than G2 cast iron, so that is what I used to make the guides I installed after re-rebuilding the engine after the 3500 miles of the Cannonball.

[bevanclark]

Great info, exactly what I needed thank you very much.
Cheers,
Bevan

[nevhunter]

The BSA slopers have a FAIR bit of trouble with the valve guides. The guides are not very long. My best fix was to make both guides greasable, Fit a very small threaded grease nipple carefully. There's not a lot of metal there. Same with the fit of the valve in the head. Good fit but not too tight. The rocker box is weak and the rockers run on small rolllers. They even reported valve guide wear problems when the were new. Loose guides can cause Valve stem breakage. The motors are quite Powerful. Keep the primary chain well oiled. Done a lot of miles on Slopers of the BSA brand. Nev

[bevanclark]

Just a followup on this: I do not have access to a lathe so am having to rely on a local engineer (who is fairly used to working on very old car engines).
He has told me that they have been unable to source suitable cast iron blanks in N.Z. in the past and is claiming that fitting bronze guide liners will work fine in a low lubrication situation. As a total non-expert, I am uncertsin how to respond, but am very wary of the likely consequences for the rockers etc if a valve were to nip up.
For those in Australia, e.g. Nev, I will be in Melbourne and Adelaide end Feb/early March - are you aware of any Oz supplier of G2 cast iron (or the Ni-Resist material mentioned by Mr Falco) ? Half a day of Googling and phoning has not identified any N.Z. supplier.
Cheers,
Bevan

[nevhunter]

I don't see bronze as a good solution in an AIR COOLED Iron head. Stainless valves have GALLING problems Nitrided or chromed stems are best. I get my guide material cast at a foundry and I had a fair bit done but nothing recent. I went into it in a serious way yeas ago. Some fine grained stuff used in OEM Mitsubishis was no good at all. I had some original late 20 AJS guides analised and copied that material. I renewed the rego on an ex bike of mine yesterday One with grease nipples fitted and it's now been on the road for 40 years. Going fine with sidecar always fitted . Pulls it easily . Nev

[cmfalco]

a local engineer ... is claiming that fitting bronze guide liners will work fine in a low lubrication situation.

Although I personally wouldn't use guide liners, bronze guide liners might work, but bronze guides won't. Starting on page 39 of my Ariel rebuilding manual, I devote a page to a discussion of valve guide materials. Although the wear properties of bronze are better than cast iron, its much larger coefficient of thermal expansion than cast iron makes it a poor choice for guides in cast iron heads. A calculation I have on page 39 shows that if the valve stem clearance is 0.0025" at room temperature, at 250 ℉ it will have shrunk to a very tight 0.0006".

https://www.amazon.com/Ariel-Chronicles ... B0BN61Z6H1

[cmfalco]

unable to source suitable cast iron blanks in N.Z.

I checked your profile and found you are a physics teacher. The good news is, as a physics professor myself (albeit, now emeritus), that means I'm obligated to send you enough of your choice of cast iron or Ni resist for free to have a pair of guides made. Unfortunately, the bad news is, after going to the garage to weigh a length of the material (85 grams/inch), I checked an on-line calculator and the least expensive way to send a 1 lb. package (~5.4" of the 1"-dia. stock I have, neglecting the weight of the box) would be $48.95(!). A shorter length wouldn't help, since the price is the same up to 4 lbs. So, sorry, I retract the offer I almost made to send it.

[bevanclark]

Indeed I am a Physics teacher . Tried but failed to retire last year when my replacement bailed out 4 days before the academic year started !

I was sent a link to a pair of nos guides on ebay U.K. that were advertised for a lot more than the shipping cost of your stock. Due to time differences, I wasn't able to get clarity on the extortionate default shipping costs that ebay was going to appy before the sale closed.

I am very keen to avoid wrecking my beautiful bike and would be more than happy to pay your costs if you'd be prepared to reinstate your offer.

Regardless of that, I am very appreciative of your advice (thanks to Nev also).
Cheers,
Bevan

[nevhunter]

Was advised against my better judgement to USE K Line in a pocket valve Harley I was putting together It did a very short time before the clearance disappeared. The interference fit disappeared also when the thin bush shrunk when heated. This sometimes happens with Gudgeon bushes too when the bronze is not good/hard enough Some of these older motors get very hot in the exhaust port area. The combustion chambers are not very efficient compared to a good OHV. Nev