Cylinders

[Boost Devil]

my celica gt4 (3s-GTE) has done about 125000 miles, i am going to get some forged pistons for it ..... but before i get the pistons do you think it benificial for me to get the cylinders bored out a size and then get an oversized pistons just to give it a good fit, would this be a good practice or doesnt it matter that much?

[daktari]

Probably best to wait till you strip the engine. Then you can measure the bores accurately to ascertain the ammount of wear.

If you just put standard sized pistons and rings in you might have to end up having to replace them sooner rather than later.

The main benefit of a rebore would of course be that your not going to have to worry too much about bore wear for the next 100k or so. And assuming you were going to go the whole hog and get the crank reground and new conrods etc your going to have a virtually new bottom end.

[Kelvyn]

You really need to know if tha bore has worn. One side of the bore tends to wear due mainly to the torque that the crank induces. With the pistons halfway up the bores you should be able to feel a slight lip right at the top of the bore. The wear is exagerrated(sp?) slightly by a build up of carbon (the top piston ring only comes so far up the bore). Honing will remove the carbon and break the glaze that forms in the bore so that the new rings can bed themselves in, but if the bore has worn then you will need a re-bore.

You should be aware though that there are minimum wall thicknesses set by toyota so that people dont go too big with the bores. There are several technical reasons for this and if you are running increased boost then its even more important that the engine block is measured before you get it bored, especially as forged pistons are so expensive (you dont want the block to crack or the head gasket going within a few hundred miles).

I'm sure there are people on here who can advise you in more detail, hopefully one will be along soon.

[Boost Devil]

Yeah that is my goal to replace the whole bottom end,TTE crank & rods and forged pistons aswell, and all apropriate bearings, thats what worried me about the new pistons if i just went ahead and put them in without having the bore taken care of would it just be a waste of time....and i think you have answerd that question for me.....if i dont get it measured and rebored it will probabley not last to long in that state, so il get it measured and see what size pistons and bore would be apropriate.

anymore comments welcome guys keep em coming

cheers

[dawesy]

for the cost of rebore (about £70) would be silly not too, just dont go above 86.5mm as this can weaken the cylinder walls. getn the head overhauled at the same time too

[Kelvyn]

Might be worth putting a post about engine mods on the MR2 section. some of the turbo owners must have gone through similar mods in their quest for more power. After all its basically the same engine.

[Boost Devil]

Im going to put new cams in the head, i know that head work is pretty expensive... what would they do to the head and any ideas how much it would cost... i suppose i could give the cams to the specialist let them fit em?

[Kelvyn]

The actual fitting of the cams is pretty straightforward, in principle its much the same as fitting the crankshaft, just on a smaller scale. If you have headwork done its mainly flowing and polishing, the can also match to the manifolds to help gas flow.

If you want to find out about camshaft fitting/removal check out http://www.mr2-tech.com/bgb/mechanical/vol..._mechanical.htm then click on CYLINDER HEAD 3S-GTE

[dawesy]

TBH port and flowing is not really important ill about 400bhp and then its just a matter of tidying up the port walls, removing casting lines etc. i was on about tacking it in and having it refaced, alkaline dipped (to clean it) and the valve seats recut. on head skimming make sure they leave a fairly rough finnish as this helps metal H/G's to seal

[Boost Devil]

top advise guys keep it coming

Cheers