Valve seat cutter

[MalcW]

Hi, I have a Model 18 that has a leaky exhaust valve. It's been recently rebuilt by a PO and the valve and valve guide are good, but it could do with the seat cutting. Any recommendations for a decent cutter? Thanks.

Malc

[Joker_Bones]

I wanted to do exactly the same a couple of years back...
I assumed I would be able to get an inexpensive cutter on ebay, good enough for limited uses, but could not find one. There were some high end ones or sets, but way more than I wanted to spend.
I took the head to local garage and they recut the valve seats for me.
Since then I have picked up a set of vintage valve seat cutters at an autojumble. They were unbranded and didn't appear particularly sharp but I managed to use them to recut a pair of valve seats recently.
I don't know what is available currently though I am curious, have you looked?

[MalcW]

Haven't looked yet, only found the issue this morning.. There was poor compression and removing the head and doing the old petrol in the head test resulted in in all dribbling out of the exhaust port. Good idea about getting it cut elsewhere.

Malc

[Joker_Bones]

The valve seats I re-cut were pitted, you say yours are good.
Maybe a trial lapping with some grinding paste, it would show you what the angles and concentricity of the seats/valves are like and perhaps further lapping will solve the issue?

[MalcW]

I think I may have found the problem. I can see a fresh witness mark around the valve stem, right next to the valve head. I think the exhaust valve guide is too far into the cylinder head and is just touching the valve head, preventing a good seal. The manual suggests there should be a circlip around the guide, but I can't see one. I'm not as familiar with the singles as I am with the twins, but does this sound feasible,?

Malc

[Duncan]

Early guides did not have the circlip and the early spring plates have to be modified to clear the circlip if one is fitted, there should be a depth stated in the manual for the length of guide extending into the rockerbox that you can check against.

[MalcW]

Yes, the manual refers to half an inch. I haven't measured it, but it's less than that. If necessary, can you fit a later circlip guide to an earlier head?

Thanks to you both for your help.

Malc

[Duncan]

Yes, the manual refers to half an inch. I haven't measured it, but it's less than that. If necessary, can you fit a later circlip guide to an earlier head?

Thanks to you both for your help.

Malc

Yes the guides are the same it just the circlip groove that's different, the circlip can be omitted if required or relieve the spring tray to clear it, check the depth to the groove first though as I cant recall what it is. Remember to heat the head and to remove the guide into the combustion chamber as there will be carbon on the end in the exhaust port.

[MalcW]

Yes the guides are the same it just the circlip groove that's different, the circlip can be omitted if required or relieve the spring tray to clear it, check the depth to the groove first though as I cant recall what it is. Remember to heat the head and to remove the guide into the combustion chamber as there will be carbon on the end in the exhaust port.

I was hoping to clean around the port end of the guide with suitably soft implements, then eat the ead and use a suitable puller to ease the guide back up a bit Do you think thay's feasible, ir should I do as you say and start from scratch?

Malc

[Joker_Bones]

I imagine what you need to know is why the valve guide is in too far... Was it inserted too far or is it loose and found its own way to that position in service.
When I have swapped out valve guides I have heated the head up in the oven 180C and even at that temp the guides were still reasonably tight and required pulling/drifting out/in.
If you heat the head and the guide is still reasonably tight then I imagine repositioning it would be fine. If it falls out I would question if it's too loose and may move in service.
Assuming it is reasonably tight and you only want to move it back a little then what you suggest is an option, otherwise remove it into the port, clean it up and refit from the top side.
The idea is not to drag crusty deposits through the hole in the head gouging as it goes.