8 replies to this topic

[SteveA]

With the GT6 back on the road I am starting to consider a new bottom end for it. The plan for it is to include cam bearings and a balanced bottom end.
To do this, the block will of course need to be line bored for the cam bearings, have the top decked and the cylinders bored to what ever pistons I use. Is there a best order for these macining processes?

[Wolfrace.]

Probably not as the casting is well and truly seasoned now.

[spitNL]

If the objective of milling the top is to bring the pistons flush with it, I'd do that after boring for new pistons.
Then do a mockup with the new pistons to determine exactly how much needs to be taken off.

I don't think it matters at what stage you have the block line bored for cam bearings.
If you're going to have the block line bored for the crankshaft too, do that before the mockup.

[RealWorld]

Hi Steve

Broadly agree BUT make sure the top/bottom faces of the block are parallel with the crank mains before you do anything.
The machine shop can do this for you (Triumph were a bit hit and miss) and then correct any run out. 6 thou or so deviance across the top face isn't unusual, and messes up virtually every other measurement you'll make is you don't get this checked/corrected first.

As Nick would say - ask me how I know...

Why you should sort the top face is obvious - the bottom less so - but as future decking/flattening etc will in almost all probability done assuming the bottom is parallel with the top, its good to get it right now.

So I'd:


- Sort the parallels (referencing to crank journals)
- Have crank ground to final sizes
- Have block bored out to desired size
- Have block line bored for the cam, bearings inserted and lap in the new cam to new cam bearings
- Tuftride crank
- Balance crank/flywheel/clutch/front pulley
- Trial fit pistons - measure - and deck the block to height of the piston with least pop-up (assuming you're decking to flat)
- Triil fit pistons again - measure pop-up on all and reduce their height to match block.
- Trial build again, just to check!
- Final build with lube for start up.

Or similar - have fun!

[SteveA]

Thanks for the suggestions guys, I will be starting off with a recessed bore block so my idea was to have that recess machined off, parallel to the main bearings and at a later time machine the pistons off to zero the deck.
I'd forgotten about tuftriding or nitriding the crank, that's another thing I'll have to look into.

[toofast2race]

Also look into getting the mains line bored or at the very least checked - mine were 0.004" out - block settling probably athough I wouldn't put it past Triump to bore it screwy.

I think the block needs about 0.035" skim to get rid of the recesses - that will bring the pistons very close to flush

[SteveA]

I was wondering about getting the mains checked for trueness, but what happens after they have line bored it? surely you end up with a larger diameter for the bearing shells to sit in?

[Nick Jones]

No, because you machine a bit off the main cap mating faces first (or off both the main cap and block mating faces if you are doing properly and have very deep pockets)

http://www.enginebui...ng_subject.aspx

Nick

[Wolfrace.]

Nick Jones, on 23 February 2012 - 09:15 PM, said:

No, because you machine a bit off the main cap mating faces first (or off both the main cap and block mating faces if you are doing properly and have very deep pockets)

http://www.enginebui...ng_subject.aspx

Nick

Ouch!

http://www.oselli.co...ces_engineering