Valve seat, rocker question

pommie john · Apr 15, 2012

I've just had the valve seats done by a ( supposedly) reputable workshop.

There seems to be two problems with the work they've done.

The inlet rockers seem to have been heated up quite hot. So much so that they have discoloured. Would this have damaged the rockers in any way? The workshop claim they only heated the head to 100C and used liquid nitrogen to insert the seats and guides, so could that have discoloured the rockers?

Here are the inlet rockers

Exhaust rockers for comparison, looking as they always have.

Also, the seats don't quite fit the ports.
The ports are slightly oval but the new seats are perfectly round so at one point there is a little aluminium to remove to blend it in, but at the opposite side the seat protrudes into the port by about 1mm. How can i blend it in without risking damaging the seat which has just been cut? I guess valve seats are very hard and not easy to grind away.

splatt · Apr 16, 2012

You probably should have removed the rockers, couldn't tell you if damaged, as for valve seats, they probably machined the seat a bit deeper cutting away a bit of the bottom of the port, the seats arn't that hard and a carbide burr will blend it in easily, it will also root your seat face very quickly if you slip,is there still aluminium under all of the seat at port throat?

pommie john · Apr 16, 2012

Quick update. I made a call to the workshop and they are going to blend the seats into the ports for me. The issue of heated rockers is all that's left.
I know I should have taken them out, but I'd only just put them back in and I originally thought they were just going to re cut a valve seat, but as they got deeper, well, you know how it goes.

john robert bould · Apr 16, 2012

The head as been heated via a blow torch! No 100c will discolour steel...If the head had been heated in an oven the rockers would be all the same colour...BRIGHT steel! or the same as you last saw them.
Rockers that colour must have experanced Direct flame contact , i would be having a fit myself at such work!

pommie john · Apr 16, 2012

john robert bould said:
The head as been heated via a blow torch! No 100c will discolour steel...If the head had been heated in an oven the rockers would be all the same colour...BRIGHT steel! or the same as you last saw them.
Rockers that colour must have experanced Direct flame contact , i would be having a fit myself at such work!

Yeah, that's what I thought. What about damage to the heat treatment or whatever to the rocker arms?

conkers · Apr 16, 2012

John,

I have fitted seats and guides (and modified) hundreds of heads professionally over the past 30 years. (Not bragging, but want to establish where my point of view is coming from).

1. I would have removed the rockers even if only cutting seats, as the filings and chips/swarf/dust could get in there. So remove them to clean now.

2. If they heated the head enough to discolour the rockers, it is possible the aluminium has now gone soft, get it hardness tested (along with the rockers) before you start pulling threads out on reassembly. I have never tested a Norton head for hardness, but just compare it to a good one (or the crankcases?). 50-60 Rockwell C is about normal for ally heads, a soft overheated (welded) head might be as low as 30 HrC.

3. If head has gone soft, get it heat treated or leave it under a bench for a couple of years to age harden.

4. Chances are that you'll have nothing to worry about... sometimes oily deposits can cause discolouration.

Mike

Hobot · Apr 16, 2012

Ah don't we love the things out of our control. Another way to remove valve seats w/o heat or machining is send to cryogenic tempering and the Al contraction will pop them right out. Don't do it now of course. Cooked looking rockers, but what else might reveal a thermal stain, spindles, their covers, studs? Cryo cycle would re-temper the rockers if need be. I'd ask shop what process might of caused differences in the rocker sets. Now is good time to grind end of rocker to the nub so solve once and for all the push rod bustle justles. Only the brave risk the oil passage in the side arm, it ain't down the middle.
Some spinldes are hard to extract d/t head holding them, but maybe shop thought the rockers were and put a torch on em.

JimC · Apr 16, 2012

The more I see here and from personal experience of bungled machine shop work, the more I realize there are few shops qualified to work on a Norton head. Are there such problems with other motorcycle heads and machine shops? Where are those who purchase Fullauto heads getting them prepped?

comnoz · Apr 16, 2012

pommie john said:
I've just had the valve seats done by a ( supposedly) reputable workshop.

There seems to be two problems with the work they've done.

The inlet rockers seem to have been heated up quite hot. So much so that they have discoloured. Would this have damaged the rockers in any way? The workshop claim they only heated the head to 100C and used liquid nitrogen to insert the seats and guides, so could that have discoloured the rockers?

Here are the inlet rockers

Exhaust rockers for comparison, looking as they always have.

Also, the seats don't quite fit the ports.
The ports are slightly oval but the new seats are perfectly round so at one point there is a little aluminium to remove to blend it in, but at the opposite side the seat protrudes into the port by about 1mm. How can i blend it in without risking damaging the seat which has just been cut? I guess valve seats are very hard and not easy to grind away.

Looking at the finish on the seats I would guess they are powdered metal seats. They are commonly used and work well. They are very easy to cut with a burr.

Looking at the rockers I would say they are damaged -just how much is hard to say without a hardness tester. Getting them hot enough to turn them blue will affect the hardness but they may still be usable. Jim

john robert bould · Apr 16, 2012

Having a good guess here.
The head was heated in a oven etc. then the "man" found a tight guide...gas bottles at hand, as the flame is directed into the head , {inside a box ]the heat is very hot. enough to "surface heat" the steel rockers...i doubt the rockers would be through heated, just surface to discolour them. I would not worry about them breaking. infact this would very,very slightly soften the forging.
Also i would'nt worry about the alloy being effected, the area around the exhaust ports get's much hotter!

pommie john · Apr 16, 2012

Thanks for the replies everyone.

I'm taking it back tomorrow to have the seats blended in and I'll question him further about heat on the rockers.

I'm hoping JR Bould is right about adding a bit of extra heat with a blowtorch. The exhaust rockers are not affected so I hope the whole head has not been overheated.

These people were recommended by one of Australia's top ( ex national champion) historic racers so I thought they would be good.

john robert bould · Apr 17, 2012

I can never understand why guide's are knocked out as a full diameter, as we all know this replacment "swage's" the guide bore.
The head would require a lot of heat to expand the holes for a bronze valve guide to become loose, bronze and alloy have close expansion rates...so heating the head will only reduce to "hold" on the guide by a very small amount.
In the past i centred the guide bore on an angle plate on the milling machine and drilled the guide leaving about 1mm left,this thin wall left offers no resistance and taps out very easy .
Must admit to the home repairer this proccess of drilling must sound behond most..it's easy for a well equiped workshop.

splatt · Apr 17, 2012

Most likely the oil in the adjuster thread has flashed over, they don't appear to have blued but more sooted

pommie john · May 30, 2012

Next problem.
I've got the head back on ( after removing the rockers again and thoroughly cleaning everything and look at the valve tips. The right rocker is nowhere near the centre of the valve, It's just touching the edge of the tip when at rest and moves a little towards the centre of the stem at full lift.
Clearly the geometry has gone awry somewhere. They have recut the exhaust seats ( I didn't ask them to) and it's my guess that they have cut the right hand seat far too much and the valve is recessed into the head.

Opinions please.

Left rocker looks OK

Right rocker. Miles out.

Matt Spencer · May 30, 2012

OFF with theyre Heads, Hang em from the yard arm . Keel Haul the knaves .

Ive found with heads the more entusiastic they are , the more of a rush & the less care .

The worlds best Bonneville head was done by a man of few words , except maybe tecnical ones .

Photo of the insides / seats , again . please .

Offset Rocker arms ??

one tends to think theyve gassed the rockers to align central , perhaps .

:|

Hope someone pulls a rabbit from the hat , should average center of stem tip through travle . As we all know .

pommie john · May 31, 2012

They are OK left to right, so they haven't been bend to centre them. They are centred using solid spacers instead of the spring washers. Nothing has changed there, it's got to be to do with valve seat recession , pushrod length, valve length or something like that.

Obviously the head will be coming off this weekend.

pommie john · May 31, 2012

OK, the head's off. It's really hard to tell, but I think the right hand exhaust valve seat is more recessed than the left, but not by much, maybe one millimetre. Would one millimetre be enough to cause this?

comnoz · May 31, 2012

pommie john said:
OK, the head's off. It's really hard to tell, but I think the right hand exhaust valve seat is more recessed than the left, but not by much, maybe one millimetre. Would one millimetre be enough to cause this?

No,
Either the guide is crooked in the head or it has been reamed/honed crooked. It appears that the seat is not concentric either. Jim

rvich · May 31, 2012

I have had a number of conversations the last few days about the lack of "apprenticeship" in specialty trades. This is another. Typically it kind of hard to convince a kid that they should be interested in learning how to work on Norton heads and if they are interested, getting them hooked up with somebody who knows what they are doing is another problem. I suggest we round up a few indentured servants and send them to Comnoz. They will thank us later.

Russ

splatt · May 31, 2012

They recut the exhaust seat for a good reason , heads been hot and had a new inlet seat fitted beside it, you have gone about this a little bit backwards as normally the ex seat would have been replaced, or both done, you have approx 1 more thread sticking out of the adjuster =1mm, try swaping valves and see if one is longer, or new valves may have a thicker face pulling the valve down a bit more.Or cut the stem right back and fit hardened lash caps and adjust the height that way
These were made 40 years a go on rooted machinery

Valve seat, rocker question

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