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Using double springs with Jag EBC springs


sparky_spit

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Hello all, I've not posted here for a very long time but spent many hours recently while recovering from cold/flu reading nearly everything on this site, and especially the engine section in some detail, so I hope you don't mind if I jump right back in with a quick question? 

My 1500 engine that's going back into my Spitfire again has just had its head back from machining (new valves/guides/seats, port matching and SSR cleaned up) and I'm fitting it up now. It's a 218141 big valve head and gives a measured 9.6:1 CR on the 1520 bottom end. The bottom end is new and has been balanced, and it has a Spitfire MK3 grind cam. The intention is to have a torquey engine for night rallies that gives good progress without too many revs and therefore noise (which is a growing issue) that I get with the 1296 that's in there now.  I doubt the new engine will be used much above 4500/5000.

The question is... is there any benefit in fitting the standard inner valve springs along with the EBC4871 Jag springs?  I understand that they are not actually needed, from what I have been reading here over the last week or so, but I'm thinking of a belt and braces approach in case I break a spring and drop a valve.  I'm using the standard spring seat, which helps locate the main spring, so it would be easy to fit the inners as well, and a bit of testing with a spring balance shows that there is negligible additional spring load on the camshaft with the inners fitted.

Or would fitting them interfere with the positive properties of the Jag springs and actually make them less effective?  Especially as both springs are wound in opposite directions?

Or am I worrying about nothing and should just fit the single Jag springs and get on with it?

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Hi Mike,

Welcome; it's good to see you here :smile:

Ref your spring question, with the kind of rev range you propose you won't be having any valve bounce problems. From that point of view, the single Jag springs will be fine on their own - even standard Herald push-on cap type springs would be fine.

Double valve springs bring two advantages:

-Provides extra security against a dropped valve should the main spring fail (as you say). Though genuine Jag springs are not likely to fail in this application.

-By having a different resonant frequency to the main spring they further reduce any tendency valve float/bounce at high rpm. Not really an issue with your proposed use.

So, some slight positives. On the negative side, the only one I can think of is increased valve train loads. I don't remember how the Jag spring ratings compare with Triumph springs (with or without the inner) -iirc someone did measure and post numbers on here -perhaps you found that? When you say "negligible additional spring loads" what sort of numbers are you getting? Needs to be measured at what equates to full valve lift.

Generally I'm wary of adding any more load than needed due to the somewhat doubtful quality of cam followers available today. You also need to check that the follower faces are flat. There are still suppliers out there (who should know better but perhaps just don't check) sending out crowned followers. These won't live long! Put two together face to face and check there is no rock. With a fine smear of grease they should stick together.

Look forward to hearing how you get on. Your old spare engine is still going btw..... about 5k miles added now. You don't have a GT6 one tucked under your bench do you? :)

Nick

 

 

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+1

TR5 double Red's, have a good rep for being good on cams, I know they are good to 7k (not that you need that) and do bring that extra piece of mind that a single failure isn't going to drop a valve. As Nick said opposite wind is intentional. Also inexpensive have a quick look on the Chris Wittor site.

Alan

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Hello Sparky spit

                               I ran the jaguar valve springs for 30,000 miles with about the same specification engine as you (mk3 grind, 9.5 to 1, cleaned up head)

I had no problems at all and cam has not worn(valve clearances not moved much)

I took it up to 5,500 rpm now and then! (crank not balanced)

I have used the red TR5 ones in the new engine as the cam is a bit more wild and crank balanced but the springs have a slightly lower rate(have a look at my crude tests)

Hello All

              I have decided (rightly or wrongly?) to have the block decked.

I took it in yesterday and the man said it would need at least 0.010" off to get a good surface and he can not re-cut the recess.

So I am having the recess removed about 0.030" the old pistons came to 0.020 below the deck and the new ones would have been 0.024" below.

So I should get a pop up of 0.005" approximately (I would rather the block surfaced and there will be less to come off the New head!)  plus these blocks are common/cheap

I have bought a set of valve springs off Chris Witor the TR5 type as I could not find any Jaguar springs anywhere.

https://www.chriswitor.com/proddetail.php?prod=CW2906

I thought I would try and compare the spring rates and this is what I found

New red (county springs about 34lbs @ 35mm and 110lbs @ 0.405" compression with 0.150" spacer(105lbs without)

White Jaguar  40lbs @ 35mm and 120lbs @ 0.405" compression'

The Newman single springs are rated @ 160lbs ??? So I think over kill for a 1500!

So what is all your opinions? (I promise not to get upset or cry) still time to change my mind as the man is busy and job will not be done until January

This is how I did it a bit crude but it was for comparison more than accuracy!

All tests with out bottom Triumph collar, I will make the 0.150" spacers in steel I do not fancy aluminium and will make them a good fit inside the outer spring to stop it moving around!

 

Roger

 

 

 

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Many thanks for the replies; this is all good stuff and gives me plenty to ponder.

I've had 3 sets of the Jaguar springs since when they were plentiful and cheaper than sweets.  I donated one set to Dale at Moordales and another set went into another Toledo head that had been skimmed for 10.1:1 CR, which is obviously useless on a 1500 road engine, and which got sold.

A while back I did some comparative tests which, while not being as precise as yours Roger, did give a good comparison between types.  I fitted up a Jag spring to a valve in the head using the standard seat, retainer and collets. Next to it, likewise with the existing springs which I'm assuming are the standard Triumph double springs.  I made a lever with a loose fitting hole and fitted this to a rocker pedestal stud, positioned so that it could be pulled down onto the valve with a spring balance. The working length of the lever was 430mm and the valve (acting as the fulcrum) was at 50mm, giving a advantage of x8.6.

The fitted length of both springs were 38mm. I compressed them to 30mm which looked about right compared to an FD1296cc engine with a MK3 Spitfire cam in it. I now realise this is probably 2mm too little and it should have been 40mm.

I was expecting the Jag springs to slightly stronger, but no.   The Jag springs took 6kg (true 51kg) to compress to 30mm and the "Triumph" double springs took 7.5kg (true 64kg) to do the same. That equates to about 112lbs for the Jag springs and 141lbs for the "Triumph" ones.  Later, I then "tested" the Jag springs with the "Triumph" inners in place and results were similar but unfortunately I didn't record the result as I was happy at the time it wasn't significant and I wasn't looking to do a proper test, but just to do a quick comparison.  So, the figure for the white Jaguar spring does seem similar to your test Roger, so I'm fairly happy my figures are more or less in the right area. I'm also thinking that the existing "Triumph" ones are probably not standard Triumph at all, but some aftermarket go-faster ones,

On balance, reading the comments above and those in the original thread, and the limits that the engine will be used within, I'm leaning towards just using the single springs,

Regarding followers, I have new County ones from Canleys.  They look good, but I will check them as you suggest Nick.  I do still have the followers that came out of that engine that you put in Chris' Spitfire Nick, and they look okay too. I'm half inclined to use those and that's why I originally kept them.  I certainly can't use the original ones; only 3 of them don't look like moon craters.  Whatever the camshaft was in this 1500 engine, it is certainly  scrap now.  It also makes me wonder whether the original over-strong springs were responsible for the camshaft's demise.

 

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Don't re-use followers unless going back to their original position in block, with the same cam they worked with before. What can be done is to lap them on a piece of wet or dry paper  (400 grade) laid on a sheet of glass, with oil until the surface is an even, silvery grey.

This process gives you a pretty good insight into how worn the followers are. Decent ones only take a few minutes to clean up. If it takes more than 5 minutes you probably shouldn't bother. I have done this in the past and that engine actually did quite a few miles afterwards without any cam problems.

On the whole I'd probably fit the new ones provided the faces are flat.

Nick

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The head is now finished and looks really good. In the end I used just the Jag EBC springs with no inners and feel happy with them.

Checking the new cam followers, they are all dead flat with no rock, and when tested will stick together as you suggest Nick.

I had some fun timing in the cam. Using the equal overlap method gives me max lift perfectly at 110deg AFTD. Well, there's an 8 degree bandwidth as the lobe goes through its own TDC from 106 to 114,  so 110 is slap bang in the middle.  What is confusing is that inlet opening is bang on 25 and closing bang on 65 but the exhaust is all over place, 10 and 8 degrees out respectively. I'm not going to worry about it, especially after a quick email exchange initiated by Markus (GT6M) explained some stuff to me. 

Anyway, after much twiddling with sprocket orientation it is now set at 105 max lift.  This is 3 degrees advanced to account for new chain wear plus 2 degrees to hopefully give some bias towards torque rather than top end power.

The engine is almost all back together now but won't go in the car yet, as we have three Chelmsford MC Friday night 12-Cars coming up before Christmas so it will hopefully be in for the new year. Fingers crossed.

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