18 replies to this topic

[garzz75]

Do i have to increase the size of piston if i send my block of for a rebore??.Never had to get an engine rebuilt before,helpful advice welcome.

[oltonlad]

yes, if you have your block rebored then you will have to get oversized pistons, the usual way is to buy the pistons first then give them to the machine shop so that they can rebore the block to match the pistons.

[oltonlad]

if the bores look ok (not worn) then you could have them honed and just fit new rings to your existing pistons.

[garzz75]

thank you oltonlad for the advice i take it thats what meant by oversize +20 etc

Edited by garzz75, 12 June 2012 - 06:26 PM.

[Sam Walters]

If you have a company who will rebore your block without having the pistons to measure, go somewhere else.

[garzz75]

thanks guys

[Carlos W]

The best thing to do is speak to the machine shop and get them to measure the bore, and look at any scores which need to be got rid of, they can then tell you what size pistons you need!

You can then buy the pistons and they can rebore to the exact size of the piston for each cylinder, taking into account manufacturing tollerances

[lrostoke]

oversize is a rebore..and will need matching pistons...plus 20 will need plus 20 pistons and rings

honing is using special stones which clean up the bore to fine tolerances..it also leaves a sort of etched finish (honed surface)

[garzz75]

thanks guys will start looking for companies in my area.

[Carlos W]

just out of curiosity, why are you getting it rebored?

[Cooperman]

The standard over-bore sizes for a 998 are +0.020", +0.040" and +0.060". If you wnat a bit more torque you could go straight to +0.080" which gives a capacity of 1061 cc.
First of all check to see if your engine has been re-bored before. On the top of each piston will be the piston part number and, if it has been re-bored and has larger pistons the oversize will be stamped into the piston top. Then decide what size you want to go to which could be the next over-bore size. Buy a set of good quality pistons this size from a reputable supplier like Mini Spares and take the block and pistons to a machine shop and they'll bore to suit your pistons. You may want to get the crank checked and re-ground as well at this time.

[bmcecosse]

In my experience - the companies doing reboring up here insist on supplying the pistons - so they get the profit on the piston sale! No pistons = no rebore...... Maybe it's just a Scottish thing......

[Cooperman]

In my experience - the companies doing reboring up here insist on supplying the pistons - so they get the profit on the piston sale! No pistons = no rebore...... Maybe it's just a Scottish thing......

It's just a Scottish thing

[garzz75]

just out of curiosity, why are you getting it rebored?

Was just that the mini had been sitting for a long time i had to put in fourth gear and rock it back and forth the unlock it am just assuming it might have cylinder scores ??? ive not yet taken the head off to look.Am just guessing.

[Cooperman]

It's probably fine. Engines don't need necessarily re-boring just because they have been sitting for a long time. Pour some diesel fuel down the plug holes, leave it for a while to soak in, then turn the engine over by hand. Once it turns freely set the valve clearances, put petrol in the tank, change the oil and filter (use a top quality 20w50 oil), put light oil in the carburettor dashpots and check that the carb pistons move freely, spin the engine over with the plugs removed until the oil pressure light goes out. Check to see that you have a good spark at the plugs. Re-fit the plugs and start it up. Run it for about 20 to 30 minutes to fully warm it up and see what it's l;ike. It will smoke a lot at first until the diesel fuel is cleared from the systems, but then it should run OK.