Sprint / TR7 Pistons

[gdc2john]

Can anyone tell me what the difference is between Sprint and TR7 pistons is. I know both arw
2.0L but sprint ones are over double the price of the TR7 ones?

[xvivalve]

TR7 pistons have a recess in their crown and are lower compression. Sprint pistons have a flat crown that sit level with the deck of the block

[cliftyhanger]

TR7 pistons are dished so will lower compression. The dish is about 1mm/40 thou.
The valve cutouts are in a different place too.

I believe some places use TR7 pistons for sprint rebuilds, and with a std cam valves should not touch pistons.
If a head has been heavily skimmed, TR7 pistons will help to restore compression ratio. Conversely on an unskimmed head they will reduce the compression a little low.

I am building a sprint engine. The block was decked 30thou (damage to the face) and I have taken 30thou off a set of TR7 pistons. It is just the edge of the "dish" I have removed, they are now almost flat. The head has had a 10thou skim. Now I have managed to shim the valves to sensible clearances, I plan to assemble the engine without a head gasket, redrill the cam sprocket to correct the timing, then check that I have some clearance. Then fit the head gasket and finish the engine build. (ie about 3 months work at the current rate of progress)

[gdc2john]

Cool thanks for that, I have a heavily skimmed head so the TR7 ones sound like the story.

[soe8m]

TR7 pistons are dished so will lower compression. The dish is about 1mm/40 thou.
The valve cutouts are in a different place too.

I believe some places use TR7 pistons for sprint rebuilds, and with a std cam valves should not touch pistons.
If a head has been heavily skimmed, TR7 pistons will help to restore compression ratio. Conversely on an unskimmed head they will reduce the compression a little low.

I am building a sprint engine. The block was decked 30thou (damage to the face) and I have taken 30thou off a set of TR7 pistons. It is just the edge of the "dish" I have removed, they are now almost flat. The head has had a 10thou skim. Now I have managed to shim the valves to sensible clearances, I plan to assemble the engine without a head gasket, redrill the cam sprocket to correct the timing, then check that I have some clearance. Then fit the head gasket and finish the engine build. (ie about 3 months work at the current rate of progress)

Better set the timing with the headgasket. The distance between the sprockets will be different with or without the gasket and so the timing.

Jeroen

[cliftyhanger]

Better set the timing with the headgasket. The distance between the sprockets will be different with or without the gasket and so the timing.

Jeroen

Good point, I will do.
I am wondering if I will need to open the angled head stud holes up a little too. I reckon that the holes will have moved about 0.5mm, so will check iusing the old head gasket.

[soe8m]

Better set the timing with the headgasket. The distance between the sprockets will be different with or without the gasket and so the timing.

Jeroen

Good point, I will do.
I am wondering if I will need to open the angled head stud holes up a little too. I reckon that the holes will have moved about 0.5mm, so will check iusing the old head gasket.

The early heads have smaller diameter holes than the later type. When both faces do mate, engine and head with a tryfit without the headgasket there's no need to enlarge the holes. When tightening, all studs first and then the bolts. Both from inside towards outside.

Jeroen