Finding top dead centre and timing the camshaft

As can be seen from my earlier posts most of the valve train is very worn.. Not surprising given the miles on the car and it's age. So as I have already mentioned I needed to replace pretty much everything apart from the sprockets (which are in good nick) and the cylinder head.

One thing that you have to consider when fitting a new camshaft is ensuring that it is timed with the crank. For example this means ensuring that when the piston is moving up the cylinder bore on the compression stroke both valves are closed allowing the mixture to be compressed. To ensure that valves and pistons move in perfect harmony the motion of the crank synchronised to the motion of the camshaft via the timing chain. Unfortunately not all camshafts are created equal and it is essential that a new camshaft is timed to the crankshaft when it is fitted.

The first stage of this process is to find top dead centre (TDC) on the crankshaft. This is the position when the piston in cylinder one (nearest the front of the engine) is at the top of it's stroke. This position is generally marked on the crank pulley, but when the engine is in bits it is good to check the marks havn't moved. There are many ways to do this but my favourite uses a device called a piston stop (see above). The piston stop is made up of a piece of steel that is bolted (in this case using the head studs) across the top of the number one cylinder. Protruding from the centre of the piece of steel is bolt. Now when the engine is rotated that the piston stops when it hits the bolt.

To determine TDC a timing disc is first attached firmly to the crank and a pointer e.g. a piece of steel wire is  attached to a bolt on the front of the engine.(see below). The crank is then turned clockwise until it touches the stop. the number on the timing disc that the pointer is next to is written down. The same process is repeated in the anti-clockwise direction. We then know that TDC is halfway between the two numbers.

 In the case below I had already lined up the crank to the TDC mark made when the engine left the factory. The two figures I read off were 26 degrees before and 26 degrees after TDC indicating that in this case the TDC index on the pulley is in the correct place. This is NOT always the case and I have seen figures that are anywhere up to 20 degrees off. In these cases setting cam and ignition timing using the incorrect marks could have caused big issues (bent valves any one!)

Fitting Valve Springs

So next need to fit the valve springs. Now in the past when I have done this I have found it quite fiddly.. The collets that secure the spring to the top of the valve are small and always flick out into oblivion if the spring isn't aligned when you release the pressure...
So this time I made sure I had plenty of collets. In fact I had twice the number required as I had stripped 2 heads, the 9.5:1 and 7:1 compression.

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LATEST NEWS: O yes, should have said, idea of fitting a supercharger is on ice until next winter. Moss have temporarily discontinued the supercharger kit while they carry out a redesign. So will be going back to plan A. Refitting the 9.5:1 and going back to Lucas Petrol Injection.

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 So back to the head.. The procedure for fitting the springs is relatively simple and requires one specialised tool, a valve spring compressor, which you also have to use to take the springs off. Stage 1. Fit the inner valve seat and the rubber o-ring valve stem oil seal. 2 & 3. fit the spring, spring cap and the valve spring compressor and compress the spring. It is worth noting here that there are 2 types of cap on the TR engine. One is in two pieces and the other one piece. The one piece cap fits on the inlet valves while the two piece is for the exhausts.

The two pictures show how the compressor is seated on the head (actually the close up shows the compressor slightly off centre, but I changed this before fitting the collets). 4. insert the two collets into the groove at the top of the valve. If you can't get them in tighten the compressor a bit. I find a bit of grease on the collets helps them to stick. now release the compressor. The release the compressor, and if all is right the collets should drop into place like those shown in 4.

Rocker shaft.. What a state..

Thought I would share with you the state of the rocker shaft.. Bare in mind I have no evidence that this has ever been changed in the life of the car which is more than 40 years and well over 100,000 miles. for the uninitiated this should look uniformly shiny... Instead it is worn in to ridges under the rockers which are easily felt with a finger.

This clearly explains why the rockers had considerable sideways play. Needless to say this will be replaced with a new shaft alongside new rockers and springs..

The cylinder head(s) return

Big day today, both cylinder heads have returned from the machine shop.. I say "both" as I ended up reconditioning both the 9.5:1 and 7:1 CR heads. Why? You ask when I am only going to use the 7:1  in the new engine.. Well slightly annoyingly I took the 9.5:1 in to be refurbished before realising that I really wanted a 7:1 head. Before I could contact the shop the head was reconditioned.. So will have to put it down to experience and now I have a nice rebuilt 9.5:1 head with new valves, seats and guides in case I go back to injection. The good side of this is that I can show both heads next to each other.

Interestingly there immediately seems to be some differences between the two heads. Try playing spot the difference:-) there are at least 7. See below for answers.

Did you find them all? RED: The large elgonated opening on one side of the head is missing in the 7:1 head. YELLOW: Two of the holes  between combustion chambers seems to be filled in the 7:1 head. Blue: Four of the holes on the opposite edge of the block to the pushrods are missing in the 9.5:1 head... So why are there differences and is it a bad thing? My guess is that in the cases where they are missing in the 7:1 head it is probably the result of less being machined of the head meaning that the passages weren't broken through. But this doesn't explain why some holes are missing in 9.5:1 head.. Interestingly the yellow holes seem to be blocked by some material different to the cast iron of the head.. So what to do? (Answers on a postcard)?

 I had a look at the cylinder block as well to see if the holes matched. Matching holes seem to be present for all so in effect neither head has all the holes found in the cylinder block. I also took the chance to measure the depth of combustion chambers to show how this changes with CR.

As you can see the combustion chamber in the 7:1 head is 4 mm deeper than the 9.5:1 head.

Fitting Rear suspension

So with the differential mount welded up it was time to begin to fit the rear suspension.
I have decided to fit a different telescopic damper system for the rear compared to the existing one (which was an after market type that bolts through the inner wing).
The replacement mounting is a CTM type which mounts to the lever arm damper mount and the rebound bump rubber mount.

CTM rear telescopic shock conversion

The only other nasty job was to drill out the mounting for the bump rubber on one of the trailing arms.. These often cause trouble as the screw that mounts the bump stop corrodes into the aluminium trailing arm. When an attempt is made to remove the bump stop it shears off. Exactly this had happened to mine so the only remedy was to drill the remains of the screw thread out, which took more than an hour, and tap a new thread. This time the bump stop was screwed in with lots of copperslip to prevent the same happening

Rear Suspension (red circle around bump stop)

Differential Carrier Trouble

One of the weak points in the TR6 drive chain centres on the location of the differential in the chassis frame. The torque generated by the 6 cylinder engine overwelms the puny factory mounting points for the differential causing it to clunk about. On my original chassis this had happened and a past owner had welded strengtheners in place (a well know remedy). However as can be seen from the previous photos of the old chassis the mountings had actually split at the top of the chasiss (not visable without removing the body!). This was all academic as I was planning on replacing the chassis. However prior to refitting the differential I noticed that the damage was not restricted to the chassis and that the front carier on the differential that connects the casing to the chassis had also cracked at some point and again a past owner had welded it up. Unfortunately they had missed with the weld and the crack still persisted.

Simple solution... Take the offending item to the nearest competant welder and get them to weld it up! All for the price of a couple of beers. Lets hope it is enough to survive the extra torque of the supercharged engine!

Valve train

Ok, so disassembling the engine showed some considerable wear. Replaced the main and big end bearings with trimetal bearings. Didn't take any pictures as it all went well.. However as always the adage of not "forcing" anything was important as the front main bearing was tight until I realised that that timing chain was preventing movement of the crank.

Next to think about the valve train. I already know that I am going to need to replace the rockers, camshaft and followers as these are all very worn (see previous post). I also need to think carefully about choosing components that will work with my plan to supercharge the engine. This means:

1) Choosing a camshaft that complements the supercharger. This has quite different requirements compared to a normally aspirated (NA), non-supercharged engine. After a lot of discussion on the TR register website two key aspects seemed to become clear. Firstly the camshaft should have minimum overlap. In NA cars, overlap, having exhaust and inlet valves open simultaneously helps flow thought the engine at high speed. In supercharged cars having both valves open can lead to the supercharger "blowing" unburnt air/fuel mixture straight through the engine. This reduces efficiency and increases emissions. So minimal overlap is required which can be equated to maximal separation between the lobes. Ideally above 112 degrees compared to the more usual 105-6 degrees of a high performance camshaft. In addition it also seems to be important to increase the lift on the exhaust valve to give time for the exhaust gasses to leave the combustion chamber..

 So... what to choose... Well looking at various sites (including this really useful one) I chose a triumph original for a Triumph 2.5 PI MkI which has a lobe separation of 110 degrees and a lift of 0.34" (better than the Triumph Tune Road 89 I had before. Interestingly there is supercharger camshaft available in from APT  (113 degrees with lift of  0.28") the US, but it is a bit too expensive for my purse

2) Ensuring that the compression ratio is below the detonation limit for the supercharged engine. Supercharging has the effect of increasing the effective compression ratio of an engine. If this gets too high detonation can occur in the engine damaging pistons etc. One way round this to increase the octane rating of the fuel, but in the UK this is not really possible. Another way is to reduce the compression ratio of the car so detonation is not reached. As standard my CP series TR6 has a 9.5:1 compression head (Casting number: 308351 Stamping: 516816). This is thought to be OK with the Moss supercharger kit but I think could be borderline. Closer examination of my head also showed it had been skimmed in the past and was closer to 10:1 which isn't going to work.

So... Back to the drawing board... Triumph offer 2 choices from the factory in addition to the 9.5:1, in the form of 8.5:1 (used in the US) and 7:1 (used in later US TR6s and Kenyan exports!) (see this site for helpful info). So I cast far and wide  and came up trumps with a 7:1 compression head from a US car (Casting number: 313248 Stamping: 218227), thanks Conrad. Interestingly this combination of numbers is not on any of the online resources, but a quick measure of the head thickness (close to 90 mm or 8.3125") shows it is 7:1. This is great as detonation should not be a problem and I should be able to run a higher boost (e.g. 10psi).

A WHIMSICAL REFLECTION:

On reflection this cylinder head has had quite a life. Cast in Canley in Coventry in the 1970s, shipped to somewhere in the US, repatriated to Nottingham in the new millennium and then returned to a machine shop (Coventry Boring) within 1/4 mile of the site of the old triumph factory in Canley for a refurb!