The Triumph Dolomite Club - Discussion Forum

Greetings.

I am currently building-up a new head for the Blue Flame (on the sitting room floor, the joys of bachelorhood!). Its already been decided by vote that she'll go back on with twin carbs but now I have another quandry.

The 1300 engine has single valve springs and the 1500 has doubles. I have many sets of double springs. so, single or double? Points for /against? Answers on a postcard please, or you could use one of those information super-motorway devices I have heard so much about. Or fill-in the handy poll featurette thingy.
Jod

Whats your target rev limit? I can't remember all the sums needed to get from that to spring force but it starts with your rev limit and F=MA. Not sure what the point would be of splitting the required force across two springs if one can do the job, at a guess to prevent valve drop if one breaks?

Tinweevil

Target rev limit is to be higher than standard, looking at 7-7.5KRPM I hope.

Actually bolx to the maths, to much like hard work. Just fit whatever Martin Bellinger has, I think his rev limit is somewhere around 17k

Tinweevil

Go double Jod. No contest really. All the factory "uprated" engines were double and you have them lying around.

Thanks Julian for your kind words. My 1300 just likes high revs......

Heartily meant as a compliment Martin. I'm just too damn inclined to reach for the calculator and theory book. Sometimes what you need it a tried and tested answer. I am the eternal procrastinator, just ask Mrs Weevil

Tinweevil

I always think that experience is a better basis than theory.

Unfortunately I have neither on the 1300 or 1500 engine!

General experience says that double springs are better for higher revs as it reduces 'valve bounce'. They do however put extra load on rest of valve train ie. rockers, pushrods, timing chain etc so fit the best that you can!

KAC will go to 6000 on single springs before valve bounce
over 6750 on double springs - runs out of cam, and valve area before valve bounce!

No comment required

BWJ

oh, didn't I mention the big valve head???

As I understand it the point of two springs is not to increase strength as you could just use a stronger spring. But that each spring will have a frequency at which they will start to bounce and by having two differnt springs they will overlap those frequencys thus reducing the tendancy for bounce.
if that makes any sense

I get valve bounce at 50 mph in second gear (yikes).

I too am preparing a head Jod, based on the 1300TC item, which itself is Spit Mk3. It has bigger valves and double springs as standard, but I will be working the breathing further. Unfortunately, to get any real benefit from this I am going to have to change the camshaft. That really means engine out.

While I do that I may as well lighten and balance the bottom end, and fit new (Vandervell or similar good) bearings.

Then there is the extractor four branch manifold and special Bellinger designed side exit enhaust system. Oh, and the twin 40's.

Thus another small job mushrooms into a big one, as I may as well paint the engine bay whilst the lump is out, and re-bush and rebuild the front suspension and subframe.

I hope to bring PKO to Stoneleigh, and after that she will be off the road for a while......