Engine update.

Much to Mrs Rusty’s dismay, I have taken the opportunity provided by the Christmas break to lock myself away in the garage poking over my partially-dismantled engine and coming up with a plan of action which balances my desire for a solid, functioning power unit with the fact that I don’t want to spend obscene amount of money in the process.

In order to completely assess the situation I continued the strip-down, starting with the removal of the rocker gear. This is attached to the cylinder head by six nuts and simply lifts off as a unit once these are removed.

Sexy, sludgy rocker gear.

With the rocker gear out of the way the pushrods could then be extracted – in true Wheeler Dealers fashion these have been pushed through an old piece of cardboard to ensure they stay with their designated cam followers and rocker arms.

Pushrods safely stored. Edd China would be proud.

Next on the list was the head removal. This is secured to the block by fourteen nuts/studs and by all accounts removal could have gone one of two ways for me – either lifting straight off or putting up a week-long fight which would involve heat, WD40, various pulling contraptions and lots of naughty words. In the end I was lucky – the nuts were undone in the opposite order from the tightening sequence listed in the workshop manual and with a couple of moderate taps from a mallet against a block of wood it came free. At this stage I also removed the cam followers, storing each in a separate, labelled bag to ensure they can be returned whence they came.

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The head put up very little resistance in the grand scheme of things.

The head itself is a bit of an unknown quantity at this stage – it’s certainly a bit coked up and will at best need a strip down, clean and reassembly but I’ll make further judgement on this a little later down the track. Hopefully there is no cracking between the valve seats. It may be that after doing the rest of the engine work I want to send the head to a professional for attention but I’ll see what the budget looks like when we get there. If the worst comes to the worst and I’m poor and miserable then I can use it as-is in the interim and attend to it some time after the engine has been refitted.

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Incidentally, the head is part number 219021 which is identical (except for the EGR port being drilled for the Australian market) to the 219016 head which is widely considered to give the best inlet flows of any of the standard Triumph 2.5 heads.

As fun as contemplating head work was, the block would be the ultimate decider in the level of work that would need to go into the engine. I was hoping that the bores would be in good enough condition for only a hone to be necessary but sadly that didn’t look like it would be the case – a couple of them having noticeable vertical scoring meaning that a full re-bore would be on the cards.

The block in all its glory.

Cylinder number 6 was the worst of the bunch:

Scoring on cylinder six.

Followed by cylinder number 3 (on the right in the below picture):

Cylinders 3 and 4.

At least this has helped me decide on what needs to be done in terms of machining – I’ll get the block re-bored and decked if necessary as well as having the main and big end crank journals ground. Hopefully I can get away with 0.020″ oversize on the bores and 0.010″ undersized on the crank but I’ll get it inspected by the machine shop before ordering any bearings and pistons in case we need to go one size further on any of those.

The only other unknown with the block at this stage was the condition of the camshaft – the first step in its extraction from the front of the block being the removal of the timing cover, which is held in place by an assortment of bolts and large screws.

Behold what lurks beneath the timing cover.

The upper timing chain sprocket is attached to the front face of the camshaft by two bolts which can be removed only once the corners of the securing tab washer have been bent back. The sprocket can then be removed along with the timing chain, revealing the camshaft retaining plate. Before removing the plate I checked the camshaft endfloat by measuring the gap between the retaining plate and the corresponding bearing surface of the camshaft with feeler gauges. The tolerance for this according to the manual is 0.006″-0.008″. Mine came in at 0.007″ so was fine in this respect. These are available new from Chris Witor and other suppliers so can be replaced if worn beyond acceptable limits.

The camshaft retaining plate.

Once the retaining plate has been removed, the camshaft can be withdrawn from the front of the engine – although the distributor drive needs to be taken out first. The workshop manual conveniently glosses over this step so my first attempt left me momentarily confused as to why the camshaft could not be freed as easily as it promised. I eventually figured it out, after which there was much rejoicing. It’s worth remembering that the camshaft should be withdrawn carefully to ensure that neither the lobes or the bearing surfaces are damaged by each other during the extraction process.

Camshaft, mid-withdrawal.

The camshaft in my engine is part number 307621 which is the stock-standard cam for the 2500 TC and S. It’s in fair condition considering its age, although does have light wear marks to some of the lobes and bearing surfaces, as well as some very minor pitting to two of the lobe tips. Its condition annoys me somewhat as it falls into the territory of neither being completely buggered or in perfect condition. My heart says if I’m going to the trouble of rebuilding the rest of the engine I should replace it, whereas my head is telling me to save the money and reuse it. Stupid boring head.

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If I were to replace the camshaft there are various options including the 2.5PI standard item (part number 308778) which seems to be one of the most popular choices of OEM Stanpart cams for improving mid-range power without adversely affecting low-end torque. Chris Witor also does a reprofiled higher inlet lift variant of this camshaft which promises to get the most out of the twin HS6 carbs (especially when combined with a slight skim to the head to increase the compression ratio to 9:1), but this isn’t a cheap option at $700/£350. Newman Cams may also be able to grind this profile from a blank for less so I’ll follow that up with them as well.

But, I’m also mindful that straying away from a stock cam could easily open the door for more expense which I can’t really afford such as a gas-flowed head, 6-3-1 manifold with sports exhaust, 123ignition with an ignition profile to better suit the cam etc etc.

For now there are just the pistons and crank left to remove to complete the strip down, as well as a few other odds and sods such as the engine front and back plates etc. Then I’ll do some research into stocking up with rebuild parts and tracking down a decent local machine shop where the wallet-emptying fun can really begin…

One thought on “Engine update.

  1. Thank you for these updates – they give me much vicarious pleasure.
    I never had to get this involved with my two 2500s – most of the time was spent on UJs and hubs, plus the traditional battle with ignition systems and rust. Not luck, but because that was 80s-90s.
    I went from Uni into a mortgage and didn’t spend as much as I should have.
    I wish you well with the rest of your project.


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