Pistons and crankshaft query - GT6

[petegardner_901]

How can I tell if the engine has already had a rebore - the piston crowns have   "073"  scribed on them - is that a standard size piston?

 

Similarly - if the crank has been reground at some point should it be marked?

 

 

Thanks

P

[Pete Lewis]

You need to measure the diameter of the piston, , std rebores would be in +0.010" +0.020 not odd

numbers like 73

 

the crank may me marked somewhere but depends who re ground it if at all its been ground.

 

you need to remove a bearing shell if its undersize it will have -0.010" or similar on the shell backing

 

pete

[petegardner_901]

Thanks pete - I'm certain now it is standard size - there are no undersize markings on the shells or crank.

 

I'm going to fit new std. rings and shells.  Should the top ring be stepped - I can't feel a ridge at the top of the bore. Engine has done about 75000 miles

 

P

[dougbgt6]

What has led you to this? You stripped it down, because? 75000 is getting towards the point to think about re-bore & regrind. My car's done 77,000 and it's had two engine rebuilds.  Before the second I replaced shells and bearings, they lasted a month before I was back to my original problem.

[Pete Lewis]

Its a long time ago I used stepped rings , not even sure if they are available

 

if you cant get a accurate measurement measure the ring gap at top of bore and compare with

25mm down the bore , then you know if its stepped.

 

you must glaze bust/ hone the bores with new rings

 

pete