Author Topic: Valve guides.  (Read 2608 times)

Offline alanp

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Valve guides.
« on: 03.08. 2010 17:06 »
I've just spent 3 hours getting just one valve guide out of my A10 alloy head. What a load of grief that was!!! The guides are the bronze ones which were fitted by SRM about 10 years ago. I heated the head in the wife's oven until I couldn't touch it with my hand but the guide wouldn't budge with a reasonable fit drift and it eventually swaged fatter than the bore in the head to ensure that I was in deep trouble. I eventually got it out by laboriously grinding away the guide down to the head surface (inside from the valve seat direction that is, in case anyone is thinking that I was trying to get it out in the wrong direction) and drilling out the guide bore to 10mm to weaken it's grip on the head.
Anyone else done this and if so how?
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Online groily

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Re: Valve guides.
« Reply #1 on: 03.08. 2010 18:03 »
I've done quite a lot of guides on alloy heads recently, British and Japanese (not mine guv). I think I've applied a bit more heat than you maybe . . . I've cooked the heads in a preheated oven at 200 C + for a good 45 minutes. With really close-fitting double diameter drifts made to suit each size, I've whacked quite firmly with a large (as in 1.5lb+ ball peen) hammer - one good well-aimed whack from a decent weapon on a firmly-fitting tool being worth a million whacks from a lighter hammer on a slackly-fitting drift. If the guide hasn't started to shift immediately (like first or second stroke), I've applied a bit of gas torch up the port and round about to get a bit more heat in, and tried again. So far so good. Some of the guides have been bronze, some chilled cast-iron. In most cases, once the guide has started, it'll carry on moving - but if a cast iron guide is rusty or pitted on the 'port' side, it needs cleaning up by whatever means, or you end up risking damaging the hole in the head and needing an oversize guide and some remedial boring..
It ain't a favourite job, that's for sure. I think you did right to grind away laboriously, thus avoiding damage to the head, but I'm guessing you could have been more cavalier with the heat.
Bill

Online RichardL

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Re: Valve guides.
« Reply #2 on: 03.08. 2010 19:01 »
I'm sure I'll be somehow corrected, but it seems heating an alloy head in the oven does little good in this case, as the coefficient of expansion of bronze is not much less than aluminum, as I recall (I'm not hitting the books right now).It seems Groily's method of targeted heat staying off the guide would work well.

Richard L.
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Offline sparx

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Re: Valve guides.
« Reply #3 on: 03.08. 2010 19:43 »
Heat the head, definitely, but chill the guide as well. I use a can of the freezing agent sold for plumbing more normally used to freeze water in pipes when the supply can't be shut off.
  A large engineers "G" clamp is kinder than a big hammer in the absence of a press, which can be difficult to position the head in.
  The same applies when fitting the new guide, heat the head/chill the guide.
Dave
Peterborough (UK)

Offline beezalex

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Re: Valve guides.
« Reply #4 on: 03.08. 2010 21:09 »
I've never had any luck trying to use heat to get bronze guides out of alloy heads for the reasons richard stated.  I don't know if chilling the guides will do you much good either since the thermal conductivity of aluminum is so good, it's hard to heat locally.  Cast iron guides seem to benefit from heating on removal from alloy heads...

Mind you, installation is a different story (heat the head, chill the guides, and your drift in all cases), but you gotta act fast.

Anyway, alan, drilling them out is a good idea, but you will still have to use quite a bit of force.

Cheers
Alex

Too many BSA's


Online groily

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Re: Valve guides.
« Reply #5 on: 03.08. 2010 21:56 »
A press is all well and good if you can get the angle right and not bear too heavily against fragile bits . . . which isn't easy. I've never dared. But heat definitely works for getting out cast-iron guides (as all would agree). Fair point and I don't know what the differential rates of expansion are for bronze and alloys various, but can just say heat's seemed to have made it easier for me. Whether it's the localised blast with the torch that really matters is a good Q though - maybe it is simply that - but so far  so good . . .
I've never used freezing spray although it would be good I'm sure, I just use her freezer for cooling new guides, an oven for the heads, and get on with it asap, with particular reference to alignment on exhaust valves with cooling/lubricating holes that have to align with any drillings in the castings.
Bill

Offline BSA_54A10

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Re: Valve guides.
« Reply #6 on: 04.08. 2010 11:37 »
Valve guide tools are really cheap and much more gentle on the head than a hammer.
Bike Beesa
Trevor

Offline alanp

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Re: Valve guides.
« Reply #7 on: 04.08. 2010 12:56 »
Trevor, can't say I've ever seen them for sale. Any idea where to get one for A10s?
Alan
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Offline Rusty nuts

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Re: Valve guides.
« Reply #8 on: 04.08. 2010 13:01 »
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Online groily

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Re: Valve guides.
« Reply #9 on: 04.08. 2010 22:21 »
Nice weapon Rusty- ought to get one!
I think the expansion factors per degree Centigrade for aluminium, bronze and cast iron are 22 18 and 10 bits per million bits respectively (according to a googling exercise I just did). Doesn't help entirely as who knows the exact composition and expansion rate of any particular alloy of alu, but it says to me that you probably want to heat heads with bronze guides good and hot, plus apply local heat off-the-guide, to get the benefit of the relatively small differential. As well as burning off any crud, carbon, etc which is trying to act like glue.
Bill

Online trevinoz

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Re: Valve guides.
« Reply #10 on: 04.08. 2010 23:04 »
Just my two-bob's worth, have any of you considered using "K" liners in your guides. This saves the trouble of removing them and all of the risks of the new ones going in skewed and loose.
I have had them fitted to the Big Valve head but have not started the engine yet. Too many projects and not enough time.
For those who have never heard of "K" liners, they are a thin wall bronze tube which is pressed into the worn guide after it is machined.
The cost is much less than a set of valve guides.
They are commonly used in car engines which do not have removable guides, even race engines.
Trev.

Offline BSA_54A10

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Re: Valve guides.
« Reply #11 on: 05.08. 2010 02:24 »
mine is a universal kit I bought from Domi Racer years ago.
As far as i know they still do them.
Harbour Freight probably sell a cheapie knock off that might last long enough to do the job once.
I have probably done near 100 guides with mine. ( mainly on cars )
If I get around to it I will take a photo
Bike Beesa
Trevor

Offline alanp

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Re: Valve guides.
« Reply #12 on: 06.08. 2010 16:12 »
Found this on the web. Good info on drilling the guide for removal but not right through so that the punch will force out the guide without expanding the guide.

'If you want to minimize damage to the head,and also make the guides easier to remove then drill them part-way through.Starting from inside the port,drill the guide bore bigger,but not all the way through.Core them out until the wall thickness is 0.040" or less on any part of the guide that has an interference fit in the head.

Find or make a punch that will fit in cored-out section of the guide and stop against the un-drilled section.The advantage of this (besides reducing the wall thickness of the guide)is that the guides are removed in tension,so they are drawn thinner when you punch them.
Put the punch in the freezer,and heat the head in an oven to 150-160 C.Each time you punch out a guide,put the punch back in the freezer and the head back in the oven.'

Alan
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Offline beezalex

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Re: Valve guides.
« Reply #13 on: 06.08. 2010 16:37 »
Good stuff, alan.....I like it.
Alex

Too many BSA's


Offline BSA_54A10

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Re: Valve guides.
« Reply #14 on: 07.08. 2010 14:29 »
Ok folks, here is the valve guide tool set.
Originally there was 3 sets of sleeves but I can only lay my hands on one at this time.
The set comprises a bent rod ( on left ) with a shoulder on it, 3 sets of sleeves , a rod with a stepped ball sized to sit in the valve seat and the handle which has a threaded hole in it to run up  down the other two rods.
The top sleeve is almost completely hollow, big enough to go over the entire guide and long enough to sit on the valve spring collar when the guide is fully removed.
The bottom sleeve is mostly solid with one end bored about 1/4 of its length so it will sit over the top of the guide on the shaft & push against the guide when installing and is flipped over so it sits square on the end of the guide for removal.It is slightly smaller diameter than the guide so it will pass through the hole in the head





Set up to pull the guide out


Set up to replace the guide
The ball end is also threaded but I can not remember if it came with more sizes to accomodate different valve diameters

Well that should get those lathes working over time



Bike Beesa
Trevor