87mm liners & pistons

[John Reilly]

Evening all!

To those that have done this pilgrimmage before me, i seek directions?

When I bought my basket-case, the engine was completely seized to the degree that the pistons had to be hacked out so buying new parts was a necessity so I thought it was a no-brainer to get the 86mm +40thou units.

Now thinking ahead to the operation and particularly to the carburettors, can anyone tell me if they had to change from the standard SU needle setup?

and/or or any other changes or refinements?

Thank you

John

 

 

[iain]

That’s a big question. It will depend on so much more than just the increase in pistons size. Changes in compression, change in cam etc will all have an effect. 
Iain

[Lebro]

Stick with standard (SM) till it's up & running, then you can experiment.

Bob

[John Reilly]

Bob, That is my intention, where I live one must think ahead as getting things takes time. I know the carbs will take care of the mixture when set up initially, I was just wondering about higher loads and demands.

I fired up the engine the other day, generally OK but a little uneven which is to be expected.

J

[iain]

John, with mine I ended up using RH needles as low end on SM was perfect but higher up the Rev range on a rolling road it was getting dangerously weak. 

Iain

[Lebro]

I have fitted RH to my HS6's as well, but too early to say if they are correct.

Bob.

[mikej]

Hmm. Still using SMs because they seem to work and set up well (under no load and relatively low revs.) So, from those than have been on a rolling road, is there a conclusion that they do run weaker (with the bigger pistons) at higher load and revs? Judging by the changing exhaust colour of mine I wondered if that's the case. Perhaps I should also experiment with RHs before charting the transition to E10, which I intend to play with.

MikeJ

[Ian Vincent]

I have 87mm pistons and HS6 carbs.  When I had my car set up on a rolling road a couple of years ago they stayed with the SY needles I was using even though there were a pair of SM needles in the glove box.

They said it slightly rich at idle but was bang on at higher revs. At my request they didn’t take it above 4500 rpm. 

Rgds Ian

Edited April 6, 2021 by Ian Vincent

[iain]

1 hour ago, mikej said:

Hmm. Still using SMs because they seem to work and set up well (under no load and relatively low revs.) So, from those than have been on a rolling road, is there a conclusion that they do run weaker (with the bigger pistons) at higher load and revs? Judging by the changing exhaust colour of mine I wondered if that's the case. Perhaps I should also experiment with RHs before charting the transition to E10, which I intend to play with.

MikeJ

That’s exactly what I found. Because my car has a 4.1:1 axle it does spent more time at higher revs even with o/d. The mixture at 3500 upwards was weak, not something I was going to risk, melting pistons is not my idea of fun. With the RH s and spirited diving I still get over 30 mpg and that’s including the 3000 mile trip to do the LBL rally in 2019.

Iain

[mikej]

On 4/6/2021 at 7:54 PM, iain said:

That’s exactly what I found. Because my car has a 4.1:1 axle it does spent more time at higher revs even with o/d. The mixture at 3500 upwards was weak, not something I was going to risk, melting pistons is not my idea of fun. With the RH s and spirited diving I still get over 30 mpg and that’s including the 3000 mile trip to do the LBL rally in 2019.

Iain

OK thanks, I will play with a pair when I can do some decent journeys. I need to set a base line so I can compare results once E10 is generally available.  My gas analyser is only a Halfords and running at 3500 will destroy it! Also, having suffered my first broken crank 2 years ago I don't like revving the engine off-load for prolonged periods.