Big valve head refurb.

[bluegrass]

Hi, I'm just servicing a big valve 940 head ready to go on a midget 1275 engine, and as its the first head i've ever tried to service and fit, thought i should get some advice.
It seems quite good generally, but i have a few questions.

1. It came with single springs. Should i replace them, or are the single springs generally re-useable and ok?
2. Although the faces seem very clean and flat, do i need to clean them off with emery paper on a flat file, or is it best to leave alone.
3. The valve faces on the head (exhaust valves esp) seem a little pitted. Would normal grinding in of valves sort that out or do they need to be cut in again by a machine shop?
4. The valves themselves are fine, but the top of the exhaust valves have some pitting , is that ok?
5. Other than the above is it good to go, or am I missing something?

Many Thanks for any help.
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[bluegrass]

More pics.[frame][/frame][frame][/frame][frame][/frame]

[bluegrass]

After quite a lot of grinding i'm left with this.[frame][/frame][frame][/frame]

[bmcecosse]

The single springs will be fine. Are the guides good? The camera may be making them appear slightly 'oval' in the picture. The combustion chambers and valve heads look very pitted - maybe that engine has been pinking/detonating badly. You can speed up the grinding process by trapping a square of emery paper with a hole in the middle under an old valve - and then spinning it in the guide with an electric drill - then follow up with a finer grade, and finally with hand grinding. Fit top hat rubber seals on the inlets only.

[bluegrass]

Thanks for the reply.

Here is a picture straight down on a guide. They don't seem too bad, a very little movement in them, but then again, i dont really have any experience to compare.
I dont have a spare valve......do you think the pitting on the valve heads themselves is something i need worry about? ie should i replace them?
I actually thought the pitted look of the combustion chamber was from the casting itself. The other side of the head has a similar finish in the none flatted sections.
When you say i should fit the top hat rubber seals on the inlets only, what do i use on the exhaust valves?
Thanks for your help[frame][/frame]

[philthehill]

Personally I would not waste my time on those exhaust valve seats they need to be re-cut.
The pitting in the combustion chamber is just sand cast finish and nothing to worry about.
No seals required on the exhaust valve guides as a bit of oil on the exhaust valve stems is a good thing.
Regarding the pitting of the exhaust valves - nothing to worry about but I would get the seats of the exhaust valves re-ground.
If there is any doubt about the inlet valve seats that is both head and valve get them done as well.
There is no point in spending all this time doing the job if the job is not done fully.
It may be worth while trying to find a valve seat cutter and doing the job yourself.
Phil

[bluegrass]

Thanks Phil,

It may be a good opportunity to introduce myself to the local machine shop, I'll probably be needing them in the future for small things that crop up. I have to take the original standard 940 head off the midget and check the valves etc on that ready to go on my 1098, so I'll do that tomorrow in case i need their help with that too. I don't mind having a go at things myself, I prefer that generally, but it depends on the cost of cutters. Are they adjustable, or do i need different sizes for different valves?

Cheers

[bmcecosse]

I've never seen combustion chambers as 'pitted' as that - and with the similar finish on the valve heads (normally smooth) I do believe there has been considerable pinking - but it's nothing for you to worry about, it's in the past. If the guides feel good, then they will be fine. Perhaps just worth checking the thickness of the head in case it has been skimmed - should be 2.750". I believe the emery paper trick will clean those seats just fine - they are not that bad, doesn't need to be an old valve, but it's up to you if you prefer to go to a machine shop....

[ampwhu]

my valve seats are slightly more corroded than this. I do like the emery cloth idea. I shall be trying this first.

[bluegrass]

Yes, its tempting, because theres nothing to lose. If it doesnt work out then just take it to the machine shop anyway. What grade of emery do you think would be 'sensible' ?

[bmcecosse]

Just use a bit of whatever you have to hand - but probably 80 to start with then maybe some 200. I suggest 'emery' because it's likely to be more long-lived than say wet/dry. But try anything you like - it won't do any harm.

[bluegrass]

Ok, thanks I'll give it a go.
Just out of interest, if i do replace the valve guides, are the cast iron ones ok?
https://www.minispares.com/product/Clas ... o%20search

[philthehill]

The valve guides in your link are very suitable for your head but you will still need to cut/finish the valve seats to the valve guides.
Phil

[bluegrass]

Thanks phil.

[les]

Each to their own but my opinion would be to fit new guides, THEN get the seats recut to the minimum amount that removes any pitting, resurface or renew valves and be happy that you've done the best with the head. When you get these situation, in the long run its not worth messing about with half measures.

[bmcecosse]

Looking again at your pictures BG - the head hasn't been skimmed. I've never understood this need to recut seats after changing guides - assuming the old guides were concentric, and the new guides also concentric ( and surely highly likely they are to a close degree I doubt they are made in far away places...) - the seat will still be perfectly placed to receive the valve head! I'm sure yours are worth a try with the emery - nothing to lose really.

[les]

Just good engineering practice, if the worn guide lets the valve move, it's possible the seat gets distorted , and if the two procedures need doing it makes sense to do the guides first.

[philthehill]

You can only guarantee that the valve seats are concentric/square to the valve guide by cutting the valve seats - there is no other guaranteed way of ensuring that the valve/ valve seat is concentric/square to the valve guide.
The valve guide is the controlling element in all of this.
I have to say that whilst the emery paper may work in some cases it is very poor engineering practice.
Phil

[bmcecosse]

Indeed - I know it's not perhaps 'mainline' practice - but it works if the seats are just needing a light refresh, and saves a lot of hand lapping. I had a set of seat cutters, and frankly found it hard going even with them - so tried the emery and it worked just fine. It's only a few seconds of spinning the valve - just enough to face off the seat. If I still had access to the nice big 45deg countersink and the vertical drill - that worked a treat when I was 'sinking' the valves on a 940 head. That was a 'lunchtime job' in the toolroom - and did a great job - but even then we trapped a piece of emery in the cutter to stop it chattering.

[bluegrass]

I've had a frustrating visit to a machine shop today. I took both this big valve head and a normal valved 940 with a view to getting new valve guides and having the seats re-cut on the big valve head, new guides and asking advice with the recessing of exhaust valves in the 1098. I don't mind taking advice at all, but just felt he didnt listen. He seemed to want me to spend lots of cash having everything replaced on each head to a spec of his choosing....

I was told:

1. The big valve head needs inserts because of ridges on 2 of the seats) see pic 1
2. A skim (no checking for flatness carried out)
3. new guides: (no checking)
£200

The midget head:
1. needs to be skimmed a lot to change compression for a 1098
2. The block needs to be pocketed.



Where i could do with some advice is in second opinions on the big head valve seats. Picture 1. Do i need inserts because of the ridge around the seat, or could this be re-cut?
2. With the 1098 head, the valves seem in bad shape but the seats ok (see pic 2 of damaged valve).....is it advisable to change these valves and if so should i change guides too? In terms of recessing exhaust valves, is this something i can only determine once the head is attached to its intended 1098 engine, because i'll probably have to find a way to do it myself? Thanks for any help.[frame][/frame][frame][/frame]