Oil consumption

[Kevin H]

Are you talking about JP Pistons in South Australia?

[peterg]

Yes, having checked

[Kevin H]

Okay. I assume you are in the UK, but if you are looking at piston manufacturers in Australia then Special Piston Services are recommended ahead of JP
Special Piston Services High performance Forged Pistons (ask for Colin!). However they are probably more expensive.

This came from a friend who rebuilds Bugatti engines, and is a bit of a perfectionist.

[Geoff Dowdle]

Peterg ,
you keep talking about distortion of the block .
I have been working on Bristol 6 cylinder engines for over 40 years and have never heard or experienced distortion in the block as you described .
My guess is that the liners are badly worn which would probably cause your excessive oil consumption.
Have you measured the pistons and compared it to the diameter of the bores as I suggested earlier.

JP pistons are cast copies of the original 8.5 compression forged Bristol pistons with three wide compression rings and segmental oil rings.
In my opinion the cast split skirt piston you have are a far better designed and made piston than the JP . Why does your engine man think that your pistons are not suitable for modern petrol ?? It sounds very strange .
Post a few photos of your current pistons .

But on the other hand I have fitted the JP pistons to a number of engines and they run quite well for road use. They are quite a bit heavier than the original forged pistons .
Why do you want 9.5 pistons ? Your block and head have probably been machined a number of times over the years and the 9.5 pistons could give you 10.5 to 1 compression . Unless you are racing it is not ideal for normal road use . What octane fuel is commonly available in UK .
I use 98 or 95 octane unleaded (with no Ethanol ) in my Bristols in Australia,
you would need that at anything above 8.5

There are probably a number a different good quality pistons available in UK far better than the JP pistons .

Ross Pistons in USA make a 8.5 piston for 2 litre Bristol , they are forged , two thin compression ring , flatter crown than high domed original 8.5 .
Overall better design and quality

Geoff

[peterg]

Geoff,
Working on a now very limited budget I'm throwing out worries, possibilities and options to gain opinions before throwing cash at them.

I couldn't work out how the wear occurred where it has. Opinion is, rather than engine block problems, that it was poor machining when the liners were originally installed.

On the options front I can replace the liners and reuse the split skirt pistons my specialist doesn't like, use JP pistons, 9.0:1 Hepolite or 9.5:1 Cosworth pistons at ascending cost; or rebore to plus 10 thou and install JP pistons or Cosworth (presumably). At a higher cost I can even get new pistons made. There may be other options but I haven't discovered them yet.

I have no idea why he doesn't like them. Possibly because they are not recommended for racing?

We have 95 & 98 octane here and I have no problems running my Gold Star (9.5:1) on 95, hence the consideration as the pistons are available.

If other pistons are available in the UK I would like to know and whether it is safe to rebore the liners as Bristol's didn't recommend it.

[Geoff Dowdle]

peterg,

BCL as far as I know only ever supplied STD or 0.010 oversize pistons .

In Australia we have been using 0.020 JP Pistons for about 20 years .
I have a set of 0.030 JP Pistons in one of my 400's and have only done about 15,000 miles but no problems yet and don't expect any.

What is the cost of Hepolite 9.0 pistons ?? The flat top split skirt pistons that I assume are with your engine are probably Hepolite

Geoff

[peterg]

The Hepolites are £828 inc VAT for the set plus delivery (I assume).

Bottom line is the car is apart at my specialist, so I am over a barrow. Final decision is to rebore and fit Cosworths (because that is what he does & is comfortable with), at a great cost. The crown of the pistons will be shaved to get as low a compression as possible (down to 9.75 as std and 9.5 if possible).

To fit new liners would have increased the costs even more.

At least I know it wasn't his fault when the engine was rebuilt. I wouldn't have expected him to measure the cylinders mid length when there wasn't any sign of wear top or bottom.