Triumphant return promised – 1970 Triumph 2.5 PI
Posted on 28. Nov, 2008 by DocDelete in Projects
Thus far I’ve avoided talking about cars, specifically classic cars. It’s a reflection of an interest that’s been on the wane for some time now. However, I am, and remain, a Triumph man at heart.
It’s with a renewed sense of purpose that I’ve decided to set to with working on my 1970 Triumph 2.5 pi. It’s a road-legal MoTd car, and was in use until recently. The engine bay lacks gloss, however. It’s not decrepit or rusty as such, but lets the rest of the car down. There’s also the small matter of the offside sill, which has had a cover sill plastered over it at some point before my tenure. It’s sound, and doesn’t bother the MoT man, but it bothers me!
Then, there’s the complication of a tuned 2500 engine that I happen to have in my possession – thanks to chum Adrian who went on a round-the-world trip. The engine was rebuilt by Jigsaw Racing, to the tune of several thousand pounds, and is their so-called Stage II development. It’s not without problems though. I discovered that some noodle had installed an incorrect rocker shaft pedestal, thus throwing out the alignment of the first few pushrods. There’s also a tapping noise coming from the area of the camshaft. Not the kind of thing you’d expect after 2000 miles of use.
I think the tapping has come from sticking cam follower buckets, several showing non-circular and uneven wear. There seems to be nothing else obvious, though further investigation of the gudgeon pins is indicated. My guess (and please, someone, contradict me – I need some help!) is that the misaligned pushrods discouraged the natural rotation of the cam buckets, and despite Jigsaw providing the correct parts, the buckets did not want to swivel, having found their ‘seats’. I’m going to hazard that a rebuild and some nice running in may solve this problem.
Another problem is the profile of the installed camshaft. After investigation I’ve been advised it’s a “300° high performance camshaft, timing 47/73 83/37, stroke 8.22 mm, recommended for race and rally engines”. (Thanks to BobbySpit.) So, far too hairy for a road car, with uneven idle, and running too rich in the revs that normal road cars achieve. The engine already has a lightened flywheel, so smooth power take-up is already compromised. Add to that the notion of bolting on my existing Lucas petrol injection system and I reckon it’s a recipe for disaster – mainly because the mechanical injection system relies on healthy engine vacuum to meter fuel. A large overlap cam like this will reduce engine vacuum considerably, causing intolerably rich running. Not good for power, economy, the engine or the environment!
So, the idea is…
- Take out existing PI engine
- Renovate engine bay
- Mate existing PI camshaft and injection gear to rebuilt Jigsaw engine
- Reinstall, reMoT and run the bugger in!
For the future…
- Restore offside sill
- Respray car (top coat only)
- Experiment with longer intake tracts, re-sited injectors and single throttle butterfly on the injection – or graft on an old Bosch K-jetronic mechanical injection system (EFI is not an option for reasons of cost).
Stay tuned, but don’t hold your breath!
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