Episode One - Intake manifolds and linkage

Initially I was making great progress, I rebuilt the spare engine for sale and put it to one side  for delivery if anyone should actually buy it (suppose I should advertise it then they might). I was then ready to start on my main engine rebuild. Unfortunately, I got ill just after Christmas with a very bad chest infection and I am still shaking off the effects now. This has had an effect on progress as my missus won�t let me out in a cold garage and I have been too exhausted to do anything anyway.

The need to rebuild  came about because of running number 5 big-end bearing at a Castle Combe track-day last year. I replaced the shells with the engine in situ as a temporary measure which has lasted until now but there is a slight knock at start up.

I acquired two brand new cranks recently, I used one for the spare engine rebuild and I have prepared the other for my main engine. This will enable me to use STD size shells and hopefully I will be able to find VP2.

I have a long list of improvements that I want to include in the rebuild. For once my intention is to be organised, and modify and rebuild items as I remove them to enable straight forward refitting when the engine is complete.

To that end I started with the intake manifolds. I hate these bloody things. They purport to be TT (I got them in a new kit off Ebay) but I think they are copies. They are roughly (sand) cast with letters in the TT logo missing. They have a thick powder coating which includes trapped dust. The interior is rougher than a badger's arse!  I decided to remove the powder coating, logos and superfluous boss for vacuum feed etc and chop down the hideous towers that the original operating bar ran in ready for M10 Rod-Ends. I gas flowed the interiors finishing off with a quick buff. In this picture you can see a bit of "before and after" with manifold on the right prepared to this stage.



My main aim was to junk the TT operating rod set-up having already converted the carb pushrods to clevis and miniature rod-ends. The TT set-up uses a 3/8" mild steel bar which was bent of course, running in nylon bushes in the moulded towers on the individual manifolds, there is no way of lining it up and they don't. I acquired a length of 10mm SS bar and 3 M10 Rod-Ends from the good ol' bay very cheaply. I simply chopped down the towers and drilled and tapped the manifolds for the rod-ends. I have several spare cylinder heads, one is knackered but makes a great jig when mounted on my engine stand as and I used this to mock up the set-up before final assembly (see pictures).










Success! There is absolutely no slack or play whatsoever in this new mechanism, so should make synchronising the carbs a much easier task.

Having now cleaned and reassembled the carbs, I have put the lot away ready for the final rebuild and started on the cylinder head. That is the next instalment if anyone is still interested and I haven't sent you all to sleep!

Looks very nice George    Is it going to miss the bonnet?

Was quiet without you last Tuesday - get well soon!!

Cheers

Nick

George,
Is there a green smiley face?  I'm envious of your skill and workmanship!

BUT, those lever arms are fixed onto the throttle bar by a screw that tightens them onto it?
Is there a flat on the bar or other means of preventing rotation?
Without something, I'd be concerned about creep under heat and vibration and loss of full throttle, or worse, a stuck-open throttle.

I'm using Prestige's version, much less impressive, but workman-like
It has mere alloy blocks in which to run the throttle bar, but the levers are welded to the bar.
I've had a stuck throttle; not the bar's fault.
Scarey, had to complete the race using the cut-off switch as an on/off hand throttle!

John

Hi mate! Thanks for the thoughts, I'm getting better, I'm back to work and "she" is letting me out to the garage for a couple of hours at a time!

It should clear the bonnet as I have set the cross bar lower than before (which already had clearance). I couldn't have it a this level before because I originally used the cold start devices and the cable between them fouled the operating levers. I've junked choke a long time ago and just use the classic Weber "6 prods and hit the button" approach to a cold start now. Setting this bar on a GT6 with the manifolds at different heights is a conundrum. I have taken the approach of having the SS bar horizontal to the cylinder head, with the down links all at the same length which means the top operating levers are at different heights. This pretty much how it was before but the advantage now is that it is tight (no slack) and smooth (no binding) in operation. It might be that I am supposed to find a compromise length adjustment for the down links to compensate for the strange alignment of the carbs, I don't know. I believe Dave has struggled with this before and come to the conclusion that you can't win!!!

Thanks for the advice again John. Those levers are as you say, just clench fitting with a allen head grub screw on the SS bar. They have been totally reliable for 5 years on the previous set-up so if it "ain't broke, I won't fix it", for once. Besides this arrangement makes sychronising the carbs easy-ish. NB: I have taken the view to keep the cross bar parallel to the head and the operating rods equal length and let the alloy "Nodding Donkey" levers stay where ever final adjustment leaves them. Not an option with fixed levers.

Much better! You can bench sync the carbs. Using the progression hole drillings once you remove the cap. Ah....errr, vaige memory they have a coreplug over them? Anyway you can see the throttle plate location in relation to the progression drillings and get some ideal of the openings in relation to eachother and agjust the lever lengths/rack to account. Fiddly job but one I'd have to do, personally. The difference between balanced and not perfect is less obvious on a 6 and the difference between awful and good is very small on a 4 cyl. The part throtte torque and driveability is ALL down to balance at all TPS.

As you say, George, if it works........
I assumed this was new kit, untried.

I'm using Lucas Pi, so the levers go the other way.  Prestige design uses adjustable length drop links between lever arm and butterfly arm, which are the Devil to get at, as the lower end is deep between the throttle bodies.    Modifying two spanners by cut 'n' welding the heads at an angle makes adjustment easy.

OK, Sod's Law rules! On the same day that I put my spare engine on Ebay, I start to strip my main engine and find that the camshaft has been trying to to make a break for freedom! No wonder I had issues last year maintaining valve clearances. A slack (almost new) duplex timing chain made me suspicious, so I grabbed the vernier gear and wobbled it - about 0.50mm of play !!! Oh, sh*t - let's examine the evidence:

This is a TH6 cam supplied by Jiggerypockery in 2004 (about 8K miles) as a set with followers and some very stiff valve springs. My knowledge has moved on since then mainly because of forums such as this. It is unfortunate, that some of our "Specialist professionals" do not participate likewise, therefore there knowledge stays stuck in a timewarp, with them trotting out the same old stuff for years? For example, I now appreciate that valve springs need to be stiff enough to prevent valve bounce for your given application, period. Not stiff enough to use as road springs on an Army truck!

Anyway what are the reasons?

1.  I naively did not fit cam bearings in my block 'cos the original bearing surfaces were perfect.
2.  Original cam bearings are not up to high lift cams.
3.  The camshaft is made of chewing gum (dunno where Jiggery get their cams).
4.  The valve springs were far to fierce.
5.  I use to have one of those extra oil feeds to the head.

Were as I feel all the above is true, I think 3 and 4 are the main contributing factors.

Problem now is can I recover the block. I have a lot invested in this 2.1L block. I will have to consult the engineering firm I use, but I don't know if they can recover the bore centres and fit Spit bearings - we'll see.

Check out the evidence:





Good news is I don't need to make a decision now whether to replace the cam with a Newman - it's a no brainer!

Oh, I also finished refurbing my head. I had already modified it in 2005, I just wanted to give it a freshen up and fit valve stem seals etc. I have now fitted some Jaguar XJ40 springs for all of 24p each! I also had another crack at the SSR after reading the excellent ncoll. A cc check proved 10.75:1 CR so I am leaving that.

Hi George, good work! Till what valve lift are those Jag springs suitable? Are they single or double? Own experience or proven?

Thx k

Blimey...... that cam is proper knackered!  How bad is the block......?

I can supply a spare block.... but only as an exchange for rebuilt short engine    I haven't been a believer in cam bearings for mostly road engines up to now but you've got me thinking!  Where the cam lobes knackered as well?

Cheers

Nick

thats one impressive cam!

Quoted from fastlorrytr

Hi George, good work! Till what valve lift are those Jag springs suitable? Are they single or double? Own experience or proven?

Thx k

GT is the originator of the Jag spring idea. He swears by 'em. They are singles and I needed to remove my doubles so that I could fit Pinto valve stem seals. Anyway, it might be that the springs I had fitted (supplied with the cam) might have been far to fierce.

Hi George,

Let us know wether your block can be saved when you find out, my original 2L block is currently sat in my garage also with chewed up cam journals so I'm interested in knowing wether it can be salvaged.

Andy

Quoted from Nick Jones

Blimey...... that cam is proper knackered!  How bad is the block......?

I can supply a spare block.... but only as an exchange for rebuilt short engine    I haven't been a believer in cam bearings for mostly road engines up to now but you've got me thinking!  Where the cam lobes knackered as well?

Cheers

Nick

I was so shocked at the journals I haven't looked at the lobes yet. I have a bit invested in this block - decked, bored to 3 inches etc, so I will strip it and take it down to Robinson Engineering to see what he says. If not I will be on the scrounge for another block.

I've not heard of this happening before. I'm still blaming the cam and springs.

The other engine is on ebay and I have had a lot of questions. Never sold on ebay before so no idea if it will sell or not.

There was a very good reason that Triumph fitted cam bearings to the only 60's Triumph engine able to rev over 6000 rpm with decent power and longevity ie the Mk2 and Mk3 spit engines. I have seen that sort of wear regularly in 2000's which see +6000rpm and run a bit of a cam + harder springs but don't use Spit bearings. Iron on iron at +3000rpm is a serious no no - Triumph were cheapskates in this respect like lots of other areas  

Hopefully the block can be recovered by line boring. Maybe all the oil escaping up to the cam was the reson for your crank bearing issues