Hitchcocks Forum

Hi all. I'm busy getting a 1951 G2 back on the road. Bought 10 years ago, not run for 7-8 years before that, so I have no earlier knowledge. The tank was full of some awful-smelling orange stuff - was that lead-replacement petrol that had gone-off?
Previous owners no longer available to ask.
SO........how do I know if it has hardened valve seats? I've had an Indian 500cc with a set of soft seats where the exhaust lost some 5mm diameter over some 400kms, hence my concern.
Any thoughts, anyone?
Cheers, ChrisD

Is it any more expensive to have a seat fitted after it's receeded than to have one fitted before?

Couple of mates with older bikes that definately don't have hardened seats were of the oppinion they'd just run them anyway and keep an eye on the tappets. If they started closing up, they'd pull the head and have them done.

My 1956 Bullet engine has standard valve seats and I have run it on unleaded or super-unleaded for the last 10 years with no signs of distress.
I think valve seat recession is more of an issue with engines that run at high revs and old cast iron car engines, such as the old B.L. A and B series engines with soft valve seats with no inserts.
I would say that most if not all alloy heads have steel inserts and are pretty safe to run on unleaded.

My 2004 350 Bullet Electra would close its exhaust clearance up after about 50 miles and lose all compression. The valve seat was very soft. I had a new one fitted about 8,000 miles ago and rebuilt it with a stainless valve; it’s never done it since.

A comparison between a British 1951 Royal Enfield and a 2003 Indian made machine is like comparing chalk with cheese.

In 1951 these engines like most others ran quite happily on the poor quality fuel then available.
I might suggest setting the valve clearances as per the book and then ride it.
Subsequent regular checks will show if there is any significant change, ie the exhaust push rod tightening up.

That’s correct, just ride the bike. You’ll soon know.

The only other way is to remove the cylinder head and find someone who can do a Brinnel hardness test on the seats. This involves dropping a diamond tipped, calibrated weight onto the material from a rig, normally a swing arrangement. The resulting dent is measured and the relative hardness can be estimated.

I know which method is more straightforward

I know which is the most expensive.

Your valve seats will already be as hard as they ever need to be. The sheer amount of hammer they will have experienced under conditions of high temperature and pressure will have seen to that within a few miles.

The removal of tetra-ethyl lead from 4 star fuel was manna from heaven for all the snake oil salesmen who prophesied the vaporisation of valve seats within a few miles that only their magical elixir could prevent. Oddly enough, the same salesmen were selling the selfsame stuff when tetra-ethyl lead was introduced back in the 1930's - when the nasty lead stuff would of course cause vaporisation of the valve seats within a few miles.....

None of my old bikes/cars have modern 'hardened' valve seats and I've never run any of them on lead-replacement stuff. None of them have ever suffered from valve seat recession.

Jools, but see my post above!

For some reason I can no longer post photos; I have an interesting one showing how far the exhaust valve seat of my bike had recessed.

Are we talking about recession occurring through impact, or stiction caused by the valve sticking to the seat?

If the latter a very week two stroke mix about 500-1 should help

I know a few people that are running the two stroke mix with no problems

Laugh if would want

Hope this helps Dai