9 replies to this topic

[nath15804]

Hi,
i have recently been told ( by a mechanic) that my cylinder head on my gasgas jtr370 needs skimming but hes not sure whether you can do it on these models because of a groove or something, can anyone shed any light on this situation, i would be very greatful.
nath

[GII]

How distorted is it? If it's not much you could try lapping it flat with grinding paste on a piece of glass

On a bike of that age and value, I'd be more inclined to try a couple of new o rings and a healthy application of good quality silicone before I paid someone to skim it.

[nath15804]

GII, on 11 October 2010 - 07:21 PM, said:

How distorted is it? If it's not much you could try lapping it flat with grinding paste on a piece of glass

On a bike of that age and value, I'd be more inclined to try a couple of new o rings and a healthy application of good quality silicone before I paid someone to skim it.

Cheers, what do ye mean by lapping it with the glass?

[nath15804]

GII, on 11 October 2010 - 07:21 PM, said:

How distorted is it? If it's not much you could try lapping it flat with grinding paste on a piece of glass

On a bike of that age and value, I'd be more inclined to try a couple of new o rings and a healthy application of good quality silicone before I paid someone to skim it.

He has said it is a tenth of a mill out by the way

[Monty_Jon]

Place the head on a piece of Very fine wet & dry on top of a sheet of thick glass or a surface table

Move the head in a figure of 8 a few time then rotate the head 90° and do the same several times (don’t remove to much metal!)

[Monty_Jon]

0.10mm shouldn't cause any problems anyway, the head bolts will pull that flat!

Edited by Monty_Jon, 11 October 2010 - 08:36 PM.

[nath15804]

Monty_Jon, on 11 October 2010 - 08:08 PM, said:

Place the head on a piece of Very fine wet & dry on top of a sheet of thick glass or a surface table

Move the head in a figure of 8 a few time then rotate the head 90° and do the same several times (don’t remove to much metal!)

ok cheers, and is a tenth of a mill a lot when it comes to cylinder heads?

[Monty_Jon]

GII, on 11 October 2010 - 07:21 PM, said:

On a bike of that age and value, I'd be more inclined to try a couple of new o rings and a healthy application of good quality silicone before I paid someone to skim it.

0.10mm is nothing on a single, tighten it properly with new “O” rings as GII says it should sort it out

Edited by Monty_Jon, 11 October 2010 - 08:45 PM.

[nath15804]

Monty_Jon, on 11 October 2010 - 08:44 PM, said:

0.10mm is nothing on a single, tighten it properly with new “O” rings as GII says it should sort it out

cheers, the guy said once he had put it bk together water was coming out, could this be because he hasnt tightened the bolts enough? how tight should they be? anyone no the figure?

[JSE]

Monty_Jon, on 11 October 2010 - 08:08 PM, said:

Place the head on a piece of Very fine wet & dry on top of a sheet of thick glass or a surface table

Move the head in a figure of 8 a few time then rotate the head 90° and do the same several times (don’t remove to much metal!)

Tape the sheet (I use 280 or 320 grit) to the glass with some masking tape to make it easier and use a little water on the paper. As you only need to take off .004" total the lapping will remove about .002" from each side to square it up, so you should be o.k. Be sure to grease the o-rings before installing them so they can settle in the groove.

Jon