Motor Specs for 96 270

[rev. victor]

Here's a tech question for the crowd. I'm tearing down the motor in my 1996 GG 270. This fall the motor started knocking bad. I pulled it apart and the big end rod bearing is gone. I found a supply of parts but can't seem to find the spec's for bore size, crank journals, etc. I scoured the web but no luck so far. Does anyone have the knowledge I seek? Any help or hints are welcome.

[jse]

Here's a tech question for the crowd. I'm tearing down the motor in my 1996 GG 270. This fall the motor started knocking bad. I pulled it apart and the big end rod bearing is gone. I found a supply of parts but can't seem to find the spec's for bore size, crank journals, etc. I scoured the web but no luck so far. Does anyone have the knowledge I seek? Any help or hints are welcome.

I'm not aware of any service manual, hard copy or web based, that would have the spec.'s you are looking for.

Rod big ends are usually set-size as you'll be replacing the rod/bearing/journal as a unit.

As for the piston, there should be a letter stamped on the crown as to it's size and the cylinder will usually have a corresponding letter stamped on the back or on the gasket surface.

Jon

[rev. victor]

I'm not aware of any service manual, hard copy or web based, that would have the spec.'s you are looking for.

Rod big ends are usually set-size as you'll be replacing the rod/bearing/journal as a unit.

As for the piston, there should be a letter stamped on the crown as to it's size and the cylinder will usually have a corresponding letter stamped on the back or on the gasket surface.

Jon

Jon,

Thanks for the response. You are always so helpful. I will do just that, replace everything. Thanks again.

[jse]

Jon,

Thanks for the response. You are always so helpful. I will do just that, replace everything. Thanks again.

The rod "spec.'s" should be easy as the parts needed will be the rod (outer race), the crank pin ("inner" race) and the bearing and any good crank guy will know how to set the side clearance when pressing the crank. You probably want to replace the seals and crank bearings, which is normal proceedure in an engine that old and the piston pin bearing also.

Check the cylinder lining and if it's in good shape find the letter marking (A,B,C etc.) and you should be able to put the next larger piston in with little problem as the normal wear will be about the difference between the piston sizes. So if the have an "A" cylinder, you can put a "B" piston in. Piston ring end gap is .1mm per inch of bore and piston skirt clearance should be in the neighborhood of .0015 to .002".

Use a caliper and measure the thickness of the old cylinder base gasket(s), which will give you a place to start for setting the squish clearance. Adding a few thousands for gasket compression, you'll have an idea of what gasket(s) to use to get the appropriate thickness. Using soft solder inside the assembled cylinder, measure the squish clearance and you'll want to have it at about 1mm or .039".

If you run into trouble, if you want, you can PM or e-mail me or contact me off the GasGas USA and UK websites under "tech" or "support", but if you are in the UK, you can't beat Kevin Hipwell's advice, he knows more than I do. You can also post to this forum and tap in to a huge amount of experience from all over the World.

Jon