Oversize valve guides

[limeyrob]

Stripping the ally head.  Both exhaust guides have been moving, one pushed out with hand pressure, one took a gentle tap. CI guides and both measure up at 0.562" OD.  I'll replace with oversize bronze.  Curiously valve stems show no wear neither do the inlet guides (also CI) but bore of exhaust guides is heavily worn.  Its had guide oil seals fitted which I'm sure carry a lot of blame, they won't be going back on.
I can get guides in + 2 thou and + 4 thou, I'm thinking heat the head to 150C and use + 4, is this a good plan?  Thanks

[berger]

when i were a lad [ a very long time ago as in teen years ] i took my head [ ally cylinder head  that is ] to an engineer geezer with some cast iron valve guides for him to fit and cut the seats etc, at the time my old man was poorly and bed bound so i had to just go elsewhere and not bother him or i would have got a severe telling off from mummy!!!!! she even told all the farmers and vacuum cleaner and washing machine geezers and bike racers to bugga off because he was really ill and wasn't doing anymore jobs for a while. he was ill  from standing in his freezing workshop on one leg using his one eye doing them jobs to keep them happy.. sometimes at midnight and into the early hours with drips from his nose falling into his socks..  [ he couldn't wear boots or shoes after smashing himself up badly in fog on his rudge before i was an entity in the world. anyway the engineer geezer gave me a telling off , he said i shouldn't be giving him cast iron guides to fit in an ally head and the bike shop who sold me them should know better .  so after all this cast iron valve guides should not be put in ally heads.

[muskrat]

G'day Rob.
The guides only need a 0.002" interference, you really need to know the size of the holes. I use an expanding reamer.
Valve guide seals are only used on the inlet. Were they fitted to the exhaust?
Cheers

[limeyrob]

I feel the same about CI guides, I'll leave the ones on the inlet as they have very little wear and are in line but exhaust will be bronze.  Yes seals were on exhaust and it looks like they have been running very dry.  I don't like valve seals on old engines, I'd rather see a puff of smoke on the overrun.  My daily driver has a Perkins engine with no valve seals and its fine.
Thanks for the advice for 2 thou, I'll get measuring. I like the idea of using an adjustable reamer, there's a chance the bores are out of round so this would kill 2 birds with one stone.

[trevinoz]

Interesting comments on guide material.
BSA initially fitted bronze guides to alloy heads but later changed to cast iron.
I have always used cast iron and I am happy with them.

[berger]

Trev PRICE!!!!! they wanted a new dress  for the wife ,

[limeyrob]

Interesting, I've had C11, B31, B40, DBD34, A10s and A65 and all had bronze guides. Rebuilt the top end on the A65 and don't recall it having CI guides (it was 71 OIF).  I suppose it's a case of sticking with what you know.

[JulianS]

Below is what Trev refers to.

[sean]

Interesting comments on guide material.
BSA initially fitted bronze guides to alloy heads but later changed to cast iron.
I have always used cast iron and I am happy with them.

my 62 super rocket had the cast iron guides ....one exh guide had a piece broken off ....I replaced them all with colisbro ones from SRM + .020 and turned down to fit each individual hole they were all slightly different .

[limeyrob]

That BSA tech note is interesting.  Pity they don't give the actual dimensions.  My old guides measure up as 0.562-0.563 so they are 9/16 with no external wear, internal wear is 0.010.  Looks like they may have only just started to move in the head.
Its a very odd engine and a lot of the recent work makes no sense.  It came built up - head torqued down with a clean bores and pistons, new big ends but 15 thou end float, mis-matching cases (not a set), a 1/8" compression plate and 8.5 pistons yet in the box with it was a cylinder with 7:1 pistons, a big journal crank and the matching number pair of cases.  Why bolt up a head with 10 thou of slack in the guides?  I'm having to tear everything down and assume nothing.
Adjustable reamer in the post so I will clean up each guide hole then get a decent measure and aim for 2 thou interference fit.
The coefficients of expansion are roughly:
Alloy head 13
CI guide 6
Bronze guide 10
("^6/F)
This suggests that the bronze guide will be less likely to loosen in the engine gets too hot.

[chaterlea25]

Hi Rob,
Be very careful using an expanding reamer
Take very small cuts at a time.
They can dig into the alloy and produce ridges where oil will leak down..
I would have checked the guide bores with snap gauges and micrometer, or even see if a 9/16 reamer would rub she surfaces clean .. the std guides come 1.5-2 thou over nominal size.
I hear the alloy heads to 200-250 degrees and freeze the guides.
I put a bit of high temp sealer around the guide near the shoulder to help stop any leakage

John

[sean]

Hi Rob,
Be very careful using an expanding reamer
Take very small cuts at a time.
They can dig into the alloy and produce ridges where oil will leak down..
I would have checked the guide bores with snap gauges and micrometer, or even see if a 9/16 reamer would rub she surfaces clean .. the std guides come 1.5-2 thou over nominal size.
I hear the alloy heads to 200-250 degrees and freeze the guides.
I put a bit of high temp sealer around the guide near the shoulder to help stop any leakage

John

I believe he is using the reamer as a measuring tool .

[limeyrob]

You are both right!  I was using it as a measuring tool but even then and with care I found it dug in.
So I got a decent measurement AND I may have made things slightly worse.  Problem solved (so far) by ordering the +14 guides.  i was going for +4 but they were out of stock everywhere I tried so that decision was made for me.
I dropped the crank and cases off for regrind and hone/line bore on Monday and while I was there asked about guides.  They said they were happy to do the guides - size, skim seat etc so my plan now is to step away from the bench and hand the head and new guides over when I collect the bottom end.
Was very pleased to find a decent machine shop who could do the work.  Our local one closed shop at Christmas, the next one is only taking vintage Bentley stuff and so busy they didn't want my business, the next one got "beware they are scammers" reviews so i was close to giving up when I found a great place about 35 mins drive away in Bracknell.
I'm hoping to use the existing valves, they look hardly worn but coked up, inlets valves and guides are good.  New springs on order.  This is a "recommission" of a basket case not a restoration so I want to keep on top of the budget.

[bikerboy]

reviews so i was close to giving up when I found a great place about 35 mins drive away in Bracknel
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I live in Bracknell and if its the one I am thinking of (the only one there I think) I would be a bit wary I am not impressed

Depending on where you are coming from Roe Engineering in Church Crookham is excellent. He has an old Triumph himself so is well up on vintage bikes and what is what

He is also extremely helpful