The Triumph Dolomite Club - Discussion Forum

I know there have been a great number of threads on this sort of issue but I have a couple of extra questions that I couldn't find in other threads.
As the title says I'm going through the process of identifying the cause of a misfire on my sprint.
It came along relatively suddenly although it has not run brilliantly since it returned to the road ~100 miles ago.

Today I set up the carbs which ran well and smoothly up the rev range when the car is stationary. It's always been a little lumpy which I put down to the STR 091 cam?
I checked the timing which was 18deg before TDC which seems a bit much but it does run well when the car is stationary
It's got an optronic ignition and a Lucas BLD 105 coil.
The coil feels really hot so this is my next suspect.

So, is this the best suited coil? If not what is the best?

Also any recommendations where to buy a decent quality rotor arm and dizzy cap? I tried the club but they are out of stock and I want to get on the road soon

Cheers

Alex

Sorry I should have said the end has run very well the same set up - prior to nearly losing the engine to a failed cam chain tensioner.
It was dyno'd at 139bhp and felt fantastic and really lively.
Now it feels like it wouldn't pull the skin off a rice pudding.

I'm no expert on warm Sprint's, but 18°BTDC is a lot of retardation at idle, it should be nearer 10° BTDC (static/dynamic), according to the label on my bonnet.

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Current fleet: '75 Sprint, '73 1850, Daihatsu Fourtrak, Honda CG125, Yamaha Fazer 600, Shetland 570 (yes it's a boat!)

Past fleet: Triumph 2000, Lancia Beta Coupe, BL Mini Clubman, Austin Metro, Vauxhall Cavalier MK1 & MK2, Renault 18 D, Rover 216 GSI, Honda Accord (most expensive car purchase, hated, made out of magnetic metal as only car I've ever been crashed into...4 times), BMW 318, Golf GTi MK3 16v x 3

Have you double checked the cam timing? If not Id start there

Tony

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Membership 2014047

Mine ran best at 15deg BTDC and it ran a Piper 270 cam. I am sure I remember that full advance of no more than 31deg was good for the Sprint when flat out. Are you sure the cam is correctly timed after the disaster?

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track action maniac.

The lunatic is out................heres Jonny!

The coil feels really hot so this is my next suspect.

Alex[/quote]
Yes, I'd do the same. On a road going car the coil should only ever be just "vaguely warm" after a run. Assuming the ballast circuit if fitted is working O.K. In my experience coils that run hot are faulty. Sorry I don't know what the equivalent of the DLB105 is these days.
Tony.

Thanks for the responses.

When you guys say cam timing do you mean setting up the vernier pulley?
In which case I'm not sure that it is correct as I farmed this work out as I didn't have the time as well as thinking I didn't have the skills.
Given the pigs ear that the rolling road company left the carbs in (Front carb throttle arm not engaged with it's linkage and other issues) I'm sure I could learn as I go.
I had a genuinely great day yesterday setting up the Carbs and checking the timing - Two things I have always shyed away from for fear that it's black magic!

How do I go about checking the cam timing? Is there a simple check or start from first principles?

I think I'll change the coil anyway and see the response. At least that will eliminate one thing.

Cam timing check in basic form is quite easy. Get No1 cylinder on compression TDC (the timing marks on the pulley should be near enough initially). Dont forget there are 2 TDC's when using the timing marks, one for No1 and one for No4, thats why you need it on compression on NO1. Then with the oil filler cap removed, if you look carefully you will see the alloy cam cap has a line cast into it. This gap (line) will line up with a line on the camshaft itself (the steel bit). A couple of mm either way wont be miles off but 5mm for eg would be a problem. Remember, when turning the crank to get the TDC marks inline ONLY turn the engine in its normal rotation (clockwise as viewed from the front). If you go past the marks, turn it backwards TOO much then sneak up to it in the correct rotation again. Hope that makes sense, Im typing fast (at work lol)

Tony

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Membership 2014047

We do have some cam timing figures on another thread. IIRC the STR91 and similar should be 106 degrees after TDC No1 and 2 inlet valves peak opening. (16 valve engine of course both on no1 cylinder)

You can get degree wheels cheap enough or even print one yourself. Put this on the crank pulley and position the crank at 106 ATDC.

If you dont have an adjustable wheel then you will have some trouble getting this right with the standard timing sprocket. I would then disconnect the top sprocket from the cam and turn it (the cam) with a big spanner with a dial gauge on the inlet valve bucket. Rock it around the peak opening until you are happy its "in the middle". Then you can see how far off your cam sprocket is from the holes in the cam. It may still bolt straight up in which case you have a result. If it doesn't at least then you know what's wrong.

When I changed my cam umpteen years ago not only did the seller fail to tell me the new valve clearances, he also failed to tell me the timing. I sorted it all after as you describe "lacking the ability to remove skin from rice pudding" lack of performance and deafening noise with the right shims and an adjustable pulley. Then it went like an absolute rocket and some 50k miles later still does.

If you are running a DLB105 then you must be running unballasted. It shouldn't be hot.

Jonners

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Note from Admin: sadly Jon passed away in February 2018 but his humour and wealth of knowledge will be fondly remembered by all. RIP Jonners.

Brilliant, thanks again for the info chaps.

I'm a bit tied for time at the moment so I may not get straight back about the results.

I've ordered a new coil so atleast I can eliminate that.

Jon : When you timed in your cam did you use a TDC setter tool or go by putting your finger over the spark plug hole?

I had just rebuilt the engine and had the bottom end all balanced so I knew the tdc mark on the timing case was accurate. With the cam cover off you can tell if its the right tdc - no 1 firing. Then I had a degree wheel stuck on the crank pulley to set it at 106 ATDC.

Just an FYI the scribe line at the other end on the flywheel and end plate is not usually that close....10 degrees or so was thought good enough
but the timing case marks are usually pretty good.

Jonners

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Note from Admin: sadly Jon passed away in February 2018 but his humour and wealth of knowledge will be fondly remembered by all. RIP Jonners.

So,
I've changed the coil.........no real difference.

I then set the ignition timing to 11deg. It feels a load better but not perfect up the rev range, however in the final 1k-ish to the red line it pulls like a train. However I have to have my foot buried to get this. Anything less than a planted foot and it's ok but not great. It feels a little more like poor fuelling? Perhaps I'll have another go at setting the carbs up.

I will check cam timing but I would like to get some miles under its wheels.

Now I'm not sure if I'm remembering how it drove wrongly or I've just got so used to driving a modern I need to relearn classic driving?

It drives cleanly enough and​ is no slouch and more than holds its own in modern traffic.

I think I need a comparison!!

Scratch my last post!

It's back to running poorly and struggles to rev above 5k.

Cam timing check here we come.

This car is annoying the life out of me. At the moment I just want to walk away from it entirely.

My coil fried because the ign timing was too advanced, felt good to drive though.

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NRW 581W Sprint


On the motorway no one can hear me sing!
Construed as a public service, self preservation in reality.

I really do feel for you.

I had a very similar problem when I first got my 1850. I went through everything that I could think of.
I had been running it with the air filter off and the breakthrough came when I put it back on and it improved things.
I swapped my carbs out for the ones on my Herald and that showed me where the problem was.
I never really did find out what was wrong but a bit of a recon on the carbs sorted it out.

I realise that it is unlikely that you can get hold of a pair of Sprint carbs but if so, they are easy to swap and would eliminate one element.

Again, I feel your pain, it drove me crackers.