4 replies to this topic

[cossy820]

hi all, have just stripped my 998cc engine down as after rebuilding it a year back it was passing a lot of oil through exhaust, 5l in a 1000mile journey to be precise!! pretty sure it's not valve stems as i had new valve guides fitted as well as new stem seals. I presumed therefore that the oil must be passing up from pistons.
I have been measuring piston and cylinder no1 this eve and have the following measurements

Bore: top-64.56mm middle-64.57mm bottom-64.59mm

Piston: crown-64.02mm skirt-64.4mm

Am i write in thinking the clearance on this is to large for a 99h engine, and as such will require new pistons as well as rings?

Also am i right in thinking that these are standard size pistons??

thanks

[Artful Dodger]

piston rings need changing. most definatly.

it depends if the 998 engine has been bored out. if it has you need to wok out by how much and what pistons you will need to buy, i dont know the measurements but a few people on here do and im sure they will say:D

[Guess-Works.com]

What you really need to know is the piston ring gap, remove a top ring from a piston carefully, and then put it down the bore in various places and measure the gap between the ends of the ring with a feeler gauge.

I think for 998's it should be between 7 and 12 thou.

The bore for a 998 is 2.543" or 64.59mm, so there does not appear to be anything wrong with the bore size, and pistons are obviously smaller than the bore to allow clearance and room for expansion.

[cossy820]

thanks guys, most helpful,

i'll check the ring gap tomorrow and see what i get.

Also would i be right in thinking if my bores are 64.9mm, then i won't have oversized pistons/rings currently fitted?

thanks again

[Pigeonto]

hi all, have just stripped my 998cc engine down as after rebuilding it a year back it was passing a lot of oil through exhaust, 5l in a 1000mile journey to be precise!! pretty sure it's not valve stems as i had new valve guides fitted as well as new stem seals. I presumed therefore that the oil must be passing up from pistons.
I have been measuring piston and cylinder no1 this eve and have the following measurements

Bore: top-64.56mm middle-64.57mm bottom-64.59mm

Piston: crown-64.02mm skirt-64.4mm

Am i write in thinking the clearance on this is to large for a 99h engine, and as such will require new pistons as well as rings?

Also am i right in thinking that these are standard size pistons??

thanks

I'm no good with metric sizes but at 1st glance,skirt @64.4 and bore at 64.59, is that .008" (8 thou) clearance? If so its a bit of a rat's tail in a bucket fit. As I say some one do the sums but surely thats no good if its the case. Come back Martin!!