Recutting valve seats with new valves?

[koolio]

Due to a botch job engineer (now I know more of a self proclaimed amateur really) I have to ditch my old 70s CB450 K3 head which is beyond salvation and start again (please don't ask I am livid with the guy).

Luckily I have a spare head which needs cleaning up and I've ordered some new valves. The seats look ok but 2 of them have some surface rust.

Question is, is it a requirement to get the seats recut? Or can I get away with phophoric acid treating them, cleaning them up and just lapping the new valves in.

The reason is not for being cheap but valve pre-tension on this particular engine there is no way to adjust the pre-load tension so the more the seat is cut the less pre-load there is.

(This is what the mechanic did without my ok, cut the seats so hard the pre-load tension is now useless).

[YBR Ric]

Any reason not to get new valve seats fitted at his expense and then get the job done properly?

[davebike]

The trick way used in the trade

take a piece emery paper or better cloth
make a cone shape around you finger Aiming fro a 90° angle and just clean off the seat face

Then grind in the new valve

Yes I done this lots of times
____________________
Dave
NC750Xdct + others at work !
davebike1@gmail.com

[jjdugen]

Yeah, doncha just love those torsion bar valve springs.
____________________
The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
Try Soi 23 on Amazon for a good read.... Self promotion? Moi?

[koolio]

[Fizzer Thou]

In the past I have only ever had the valve seats in the cylinder head cut when the valve guides have been replaced.For just a bit of surface rust I would just lap the valves in with fine and not use course unless the seats are pitted.

Once there is an even circular band at 45 degrees,install the valves and the spark plugs and pour in some white spirit or similar.If the seats are good then there should be no liquid leaking by
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Always have a 'Plan B'

[koolio]

Yea I do acetone tests all the time, thanks for the advice.

Ok will see how I get on with this one. I would usually recut but torsion bar bs doesn't like this!

[Triton Thrasher]

Re-cutting seats sounds a bit drastic for "some rust."

Make sure the valve to guide clearance is ok, then grind them a little bit, with fine paste, until the rust is off the seat contact area and there's a grey line right round. Should only take seconds and practically zero dimensional change.
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Rrrrrrrrrrrrrrrrrr

[koolio]

Yes but new valves should equal a valve seat recut imo, even if it is a light cut.

I suppose I am a little frustrated both with getting the head done asap and the pre-load annoyance otherwise I would not hesitate to get them cut lightly.

I will see when I get there I maybe able to get away with it.

[Triton Thrasher]

[koolio]

[hmmmnz]

can you not get new valve springs with a slightly longer length, or new hardened valve seats fitted.
it seems to me that you are trying to make it more of a deal than what it is.
ok don't want to spend anymore, and you use the spare head, unless there has been a burnt out valve, i doubt that you'd need more than a simple lapping of the valves
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[Fizzer Thou]

[Snod Blatter]

[hmmmnz]

[Fizzer Thou]

[Snod Blatter]

They could get away with that because the valves are a lot smaller, so they have less tendency to float. This is a 450 with only 4 valves, they're big bits of metal to try and precisely control at 9500 RPM.

[sickpup]

And here we move into the world of blueprinting and its associated parts.

The big question here is just how much meat has he removed from the old head?
Many manuals come with a measurement that is for the length of the valve spring when in place. the way to achieve this perfect length was to either add washers that came in .01mm thickness (on GSXR oil boilers that is) or machine down the head.

In your case you could measure and have a spacer machined up to go under the valve on the head assuming that the valves aren't recessed to the point of not being much use.

[koolio]

[Triton Thrasher]

Valves can be shortened and hardened caps fitted to them. Americans seem to be mad for "lash caps," as they call them.

Valves can be altered and new collet grooves cut.

But experts' time costs money.

The 450 was a good bike, compared to the 1960s competition, but maybe not a good bike for the home mechanic, 40+ years later.
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Rrrrrrrrrrrrrrrrrr

[jjdugen]

The 450 was NOT a good bike, don't ask how I know!!!!!
____________________
The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
Try Soi 23 on Amazon for a good read.... Self promotion? Moi?

[Triton Thrasher]

[koolio]

[sickpup]

[koolio]