Author Topic: Cast Iron Valve Guides are Different  (Read 253 times)

Offline Colsbeeza

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Cast Iron Valve Guides are Different
« on: 01.10. 2018 04:04 »
I dropped the head in for overhaul to the workshop owner, and explained that I had 4 more spare guides if there was any problem. I did not speak to the bloke who did the work as he was having a day off.
When I got the Cast Iron Head back from overhaul, the bloke who did the work wasn't there, so I rang him next day.
He told me that I had given him 3 Inlet and 1 Exhaust guide. "No worries he said - I modified one of the inlets to suit".
He explained that the exhaust guides have a recess machined from the underside of the combustion chamber. He machined one of the inlet guides to suit. This was bit of a mystery to me, as all 8 guides were in there original plastic envelopes and all had identical part numbers. Without opening the packets, it was not possible to see the difference.
I then opened my 4 spares and discovered I had (not surprisingly) 3 exhaust and 1 inlet guides. ( Photo attached).
The externals of the guides are also dimensionally slightly different.
I was unaware that inlet and exhaust guides are different.
I cannot understand what the recess in the exhaust guides are for. Maybe clearance to allow for a small buildup of carbon behind the valve head?? Anyone know.??
Second lesson is always talk directly to the bloke doing the work. He had been unaware that I had spare guides.
I now need to obtain an inlet guide to have a full set of spare guides.
On the whole though, I am confident in the quality of their work and knowledge.
Cheers Colin



Colsbeeza
Australia

Online beezermacc

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Re: Cast Iron Valve Guides are Different
« Reply #1 on: 01.10. 2018 08:19 »
Cast iron head guides all have the same part number so all guides are the same (originally). I have seen the recess in some modern guides but again, depending who supplies them, all four are the same, either with recesses or without. The exhaust valves get coked stems in use so a bit of a recess is probably a good idea to inhibit the coking on the part of the stem which runs in the bottom of the guide.
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Offline Colsbeeza

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Re: Cast Iron Valve Guides are Different
« Reply #2 on: 01.10. 2018 11:36 »
Beezermacc - I purchased the guides about 25 years ago, so must have been a fairly recent development before then. What you say makes sense about minimising coking.
Thanks and Cheers
Colin
Colsbeeza
Australia