s rods into a small bore block

[5portsrock]

Hi , what is required to fit s rods in to a 998 block . Also how light can s rods be safley lightened to ? Thanks

[Spider]

About 0.090 - 0.100" needs to be taken off one side of the little end. The side it needs to be taken off is the more flat side of the rod, with respect to the big end. If you look at the Rod side on, it looks almost flat, with the big end off set towards one side. It's the other side which needs thinning.

The other part is they are damn fiddley to fit. As the Rod is too fat to fit down the bore, you need to put the Rod up from underneath, as far as you can get it, with the little end above the deck, then fit the piston and press the gudgeon pin in. Likewise, a ripe bugger to disassemble too. You'll need to find pistons with plenty of meat around the Gudgeon Pin Bosses, as they need to be bored bigger to take 1275 Pins, which will need a little shortening, or JP Pistons do make a suitable piston with a pin.

You should be able to reduce the weight of the Rods by 10% with safety, and further, but you do need to be careful going lower than that, I'm sure someone else here could give some guidance on that.

Can I ask, why you are considering this route?

[5portsrock]

About 0.090 - 0.100" needs to be taken off one side of the little end. The side it needs to be taken off is the more flat side of the rod, with respect to the big end. If you look at the Rod side on, it looks almost flat, with the big end off set towards one side. It's the other side which needs thinning.

The other part is they are damn fiddley to fit. As the Rod is too fat to fit down the bore, you need to put the Rod up from underneath, as far as you can get it, with the little end above the deck, then fit the piston and press the gudgeon pin in. Likewise, a ripe bugger to disassemble too. You'll need to find pistons with plenty of meat around the Gudgeon Pin Bosses, as they need to be bored bigger to take 1275 Pins, which will need a little shortening, or JP Pistons do make a suitable piston with a pin.

You should be able to reduce the weight of the Rods by 10% with safety, and further, but you do need to be careful going lower than that, I'm sure someone else here could give some guidance on that.

Can I ask, why you are considering this route?

Hi Spider, thanks for the reply. Thought id look into fitting them as im considering making a 69mm bore small bore and i have some s rods spare . the small bore rods are probably the weak link in the engine so worth a look at doing ???

[Vegard]

Why?

[5portsrock]

Why?

Why what ? please ask if you have a question or better still can answer my original post .thanks

[Vegard]

Why bother the hassle with S rods in a small bore?

[Matt_Tupman]

Small bore rods aren't weak. Look at Mini Se7ens.

[Spider]

As the other guys have said, small bore rods are not at all weak, far from it and are easily comparable in strength to S rods. The weakest part of S Rods is the big end, they get very thin around the tops of them, either side of the beam.

If you use the small bore rods, I'd suggest replacing the bolts with Unbrako Brand Cap Head Bolts, these are Grade 12, the stock bolts are OK, but they are the weakest part of those rods.

I'd also suggest dispensing with the circlips to retain the Gudgeon Pin, they can come out or break, though they shouldn't come out if fitted correctly, but still, the odd one has been known to come out. There are a number of options here, probably the lightest would be to fit Buttons, I prefer Aluminum over Teflon. Or if you can find a set of Australian Rods circa 1965-ish to 1968 from a 998, these had press fit pins and I think the last of the A+ 998's did too.

Or, you could even look at custom rods, which IMO, are generally good value for money especially after you consider the time / cost of lightening a set off stock rods which will only be lightened stock rods! Custom ones are usually lighter and stronger.