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Author Topic: Valve won't seat!  (Read 5250 times)

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Shackeng

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Re: Valve won't seat!
« Reply #45 on: 14 March 2017, 09:17:30 »

Continual rotation in one direction doesn't work - so I was told in my earlier years, but I cannot remember the reason why. I was also told of an accessory for a power drill that mimicked the alternating-direction action of hand grinding but it's unlikely to be available still as so few people lap valves in nowadays.



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What James has done here(put valves from one used head into another) shows just how well the seats are machined on modern engines/equipment: you wouldn't have even considered doing that on an old engine with just grinding paste - you would've had both the seat and the valve reground and then lapped(which even with coarse paste is a final finishing operation) them to match each other.

I'm glad I didn't know this when I hand lapped valves on my Mk1 Consul, M2 Zephyr, Renault16 and Beetle engines all those years ago. ;D
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Marks DTM Calib

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Re: Valve won't seat!
« Reply #46 on: 14 March 2017, 11:57:25 »

Aluminium heads on an engine do not in anyway guarantee hardened exhaust valve seats sadly.....as many Rover V8 owners will be able to confirm sadly


That is not what the many Rover V8 owners I know say: you'll be suffering from knackered cams/followers/bores/ other low oil pressure related faults long before the valve seats fail. I read a letter from a manufacturer of valve seats some years ago, he reckoned that they had never(since the thirties!) sold a valve seat that wasn't suitable for unleaded fuel.

Pre 85 engines are well known for valve recession as they had a basic chilled Iron seat, this vastly increased if they operate on load for any period (so smaller cars not such an issue, Land Rovers etc, bigger problem).

There was always some confusion as Rover stated they were ok from the early seventies (they weren't but the recession was considered small.....), its when they finally opened the inlets up with EFi that they truly had to swap over to a proper hardened seat. Easy enough to track with the valve seat part numbers.
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