8 replies to this topic

[JonnyAlpha]

Hi;

 

I have an early MG Metro Head 12G940and a 12G295 Cylinder Head. As I have never done this before I need some advice on what size valve lapping tool to get.I have been looking at this one with 19mm and 22mm ends.

 

The valves on the 12G940 are 29.5mm and 35.6mm which will fit the valve s on this head I guess. According to this info, the valves on the 12G295 are 30.93 and 25.4, so again this tool would fit.

 

Also what paste / grade should I get, Chemco on Amazon here just says 'FIne and Coarse' but one answer on the page suggests that this is probably 80 and 240 Grit. The tin in only 110g is the enough for a couple of cylinder heads, or should I get separate tins?

 

On Frost here you get a 300g tin (three times as much), but in four different grades, what should I get?

 

- Fine (220 grit)

- Medium (120 grit)

- Coarse (80 grit)

- Extra-coarse (30/60 grit)

Here is the link to a thread on my cylinder head if you need to take a look.

 

 

[hunterg30]

You don't need much to do the valves. I used the fine and course . Still got plenty of it left. Just use the tool with the suckers on each end . Quite easy to do , but don't get carried away doing them

[Spider]

If you need anything courser than 220 grit, the seats need re-cutting.

[JonnyAlpha]

If you need anything courser than 220 grit, the seats need re-cutting.

I guess I'll try with the 220 and if there are still pits I'll get the machine shop to re-cut. If a valve seat is re-cut does the valve need to be modified or will the difference just be taken care of when the rockers are adjusted?

[Bobbins]

The Chemco paste you've linked to will be fine (no pun intended!), chances are that you'll only use the fine end and the tin will last many many years and do many more heads than you're probably ever likely to do. The tool you've linked to is perfect for the job as well, but when you've finished your head leave it somewhere handy ... it's ideal for getting a good purchase on those pesky GU10 bulbs that you've probably got fitted in your bathroom/kitchen ceiling making them easier to replace :)

[gazza82]

I found the rubber suckers perish way before your run out of paste!

[Spider]

 

If you need anything courser than 220 grit, the seats need re-cutting.

I guess I'll try with the 220 and if there are still pits I'll get the machine shop to re-cut. If a valve seat is re-cut does the valve need to be modified or will the difference just be taken care of when the rockers are adjusted?

 

 

Usually tappet adjustment is enough. If the Valve Seats in the head end up too deep, you may need to have them inserted, but a LOT of material needs to be removed before they get to this stage.

[JonnyAlpha]

 

 

If you need anything courser than 220 grit, the seats need re-cutting.

I guess I'll try with the 220 and if there are still pits I'll get the machine shop to re-cut. If a valve seat is re-cut does the valve need to be modified or will the difference just be taken care of when the rockers are adjusted?

 

 

Usually tappet adjustment is enough. If the Valve Seats in the head end up too deep, you may need to have them inserted, but a LOT of material needs to be removed before they get to this stage.

 

 

Thanks 

what about the machine shop comment on not being willing to put in unleaded inserts due to the minimal gap between the Inlet and Exhaust Valves on a 12G940 MG Metro Head

[Spider]

 

 

 

If you need anything courser than 220 grit, the seats need re-cutting.

I guess I'll try with the 220 and if there are still pits I'll get the machine shop to re-cut. If a valve seat is re-cut does the valve need to be modified or will the difference just be taken care of when the rockers are adjusted?

 

 

Usually tappet adjustment is enough. If the Valve Seats in the head end up too deep, you may need to have them inserted, but a LOT of material needs to be removed before they get to this stage.

 

 

Thanks 

what about the machine shop comment on not being willing to put in unleaded inserts due to the minimal gap between the Inlet and Exhaust Valves on a 12G940 MG Metro Head

 

 

Well,,, that's their call as they have to warrant the job and that's fair enough.

 

I'll add that I've done loads without issue and plenty with valves even bigger than those from the MG. Touch wood, never had an issue with any.