Boring sprint engine

[GrahamFountain]

There's a car for sale on ebay with a Sprint engine that's supposed to be bored out to 2.2 Ltrs. Does anyone know if that would still take liners back to 1998 cc, and what pistons is it likely to have at 2.2 L?

Graham

[tony g]

I'd doubt its 2.2l. Max pistons available from Triumph was 20 thou (0.508mm) and thats not enough to make 2.2. From memory when I was looking into boring and sleeving the sleeve is 1.5mm thick so 3.0mm on diameter increase. STD is 90.3mm so boring the block for sleeves could take it out to 93.3 (ish). Ill have a look at my spreadsheet on bore v's stroke and come back.

Cheers

Tony

[tony g]

It would take a 95mm piston to make 2211cc with 78mm stroke so not much chance of getting a bore that size. A 92mm subaru piston will work and leave a standard block with 100 thou wall thickness (ive measured a block with an ultrasonic tester), which is a viable option if prepared to modify gudgeon pin bush and sort valve reliefs and compression etc.

Do you have a link to the"2.2" engine?

Cheers

Tony

[tony g]

If its the TR7 Graham its not a sprint engine. I have asked the seller for details on the pistons and bore.....

Cheers

Tony

[GlenM]

If its the TR7 Graham its not a sprint engine. I have asked the seller for details on the pistons and bore.....

Cheers

Tony

It's the standard 8v 2 litre, which has the same bore and stroke, and block, as the Sprint engine, so if that can be enlarged to 2.2litres...

[tony g]

Yes Glen I realised that, but getting to 2.2 would take the bore being a tad smaller than 95mm and Im not aware of an available piston that large and the bore wont have enough meat for it.
Years ago if anyone bored a 2.0 pinto they usually claimed it was a 2.1 but it normally wasnt

Tony

If its the TR7 Graham its not a sprint engine. I have asked the seller for details on the pistons and bore.....

Cheers

Tony

It's the standard 8v 2 litre, which has the same bore and stroke, and block, as the Sprint engine, so if that can be enlarged to 2.2litres...

[Magenta Auto Sprint]

What difference would re-stroking the crank make?

In the mini world they off-set grind the crank by a few MM, it means that the thickness of the hardness is now very thin but this could add a few CC.

a bore of 93.5 and a stroke of 80mm would give 2197cc
Malcolm

[soe8m]

I think this story is b@llsh$t. Enlarging the bore that much isn't possible and of setting the crankshaft that much also. It can be done with a custom camshaft but why would one do such a thing.

Jeroen

[Magenta Auto Sprint]

Well Rob Walker makes a good living out of Bu8sh*t.

http://www.robwalkerengineering.co.uk/c ... oking.html

re-stroking a 1275 A series crank form 81.28 MM to 84MM for £150

[soe8m]

That's for mini's. In the early days the opel and BMW rally engines had it also this way and had an extra plate between the engine block and head but for these and the minis it's (small) serial production. Why would one make one new crankshaft for a dolomite just to have 2,2 liter. Doesn't make sense. Heard a lot of stories of people fitting third overbore pistons and thought they had much increased cc's. All pub talk.


Jeroen

[MIG Wielder]

Is it possible to do an offset cylinder bore on the Sprint just as Oselli do on the 1800 MGB engine to give it 2 litres ?

[GrahamFountain]

It's not a Sprint engine! That'll teach me to look properly. But that twin choke manifold must be pretty rare. Might be nice on an 1850.

Could have done the maths on the 2.2L bore diameter on a standard stroke, but I didn't know the wall thickness for a liner or the limit on boring from standard. It would seem pointless to line and bore bigger as well - I just wondered if there was a piston around with a relatively close pin diameter and the right diameter as an interim to re-lining my +40 engine. Spose I could get forged ones at +60, which might be cheaper.

Graham.

[tony g]

Ive been looking at alternative cast pistons too. I currently have a 90.5 VW air cooled piston in a sprint block. Gudgeon pin bushes were remade by me with PB1 bronze and finish honed by the guru himself Rob Walker (as mentioned above). I now have 0.9mm piston out of the block so will machine this to suit my compression and I have yet to get valve reliefs milled into the crowns.
This obviously needs a good bore to start with but after a bit more digging, I found a 92mm VW that is next on the list to try . Sprint blocks typically cost £200 to rebore so experimental work needs to be carefully chosen

Tony

[tony g]

90.5 piston by tg1mm, on Flickr

[xvivalve]

Good work Tony!