The Triumph Dolomite Club - Discussion Forum

Lads -

Been a lurker for quite a while, but I have been reading about everyone's projects. Been working on my own over the winter, not a Dolomite though. I have built a TR7 Sprint, which used the Dolomite Sprint engine. Picked up a few parts from board members, and had many shipped over to the US from England. eBay is my friend.

Picked up a 1980 TR7 drop top 18 months ago, and yanked the engine and tranny. Rebuilt the motor using Dolomite bits, and tossed back in the "Great Pumpkin" over the winter.

Thought I would share some photos.

The big deal is that I get tested for emissions here in the people's republic of Oregon, so I needed to engineer all the bits so that I could strap on the emissions gear from the 7. I reused the Zenith carbs, and welded in some bungs so that the air injection was operational. One big challenge was getting the Rimmer Brothers header to fit on a left hand drive car. The steering shaft prevents installation of the header as is. Much heating and hammering ensued, and colorful metaphors were heard wafting from the workshop.

Will be hanging out and posting from time to time.

Cheers,

Vance

new to this wrote: ↑Sat Feb 15, 2020 9:08 pm Looks a tight fit,whats the rest of the car like any pictures

Dave

It probably would not be such a tight fit if I had gone with SUs and some sort of pancake filters. Also, I get tested for emissions so I needed to transfer over all the emissions stuff, so the Zeniths made sense, along with the heat stove and associated air box.

Many startup issues - mostly vacuum leaks causing very rough idle and stalling. It took two rounds of finding and fixing vacuum leaks before it would start reliably.

The car itself had a single previous owner from new, who had recently died. The friend of the family selling the car said the owner babied the car. I could tell from numerous clues that this was not necessarily the case. The choke was inoperative, the shift extension was barely attached to the gear box, making gear selection all but impossible. No turn signals, dead radio, howling brakes, blah, blah, blah.

All easily fixed. But the federalized TR7 engine is a real dud, and was barely competitive back in the day. Hence the Dolomite Sprint motor.

There were only about 70 original TR7 sprints made, all coupes and all sold in the UK. Plans to market the TR7 Sprint through dealers never came to fruition. I was bored, and thought it would be great fun and easy since the engine had been fitted by the factory, however briefly.

A bit more work than I expected, especially fitting that header. Easy if it is a right hooker, not so easy for LHD. But I got the job done. Well, almost...

Vance

Lads:

Just an update, and perhaps a bit of whining.

The world outside of the US has fewer things to deal with, notably emissions, when hip deep in a resto project.

The big thing at the moment is getting everything tweaked in, an experience we all go through. The TR7 sprint has a wonderful bit of mischief called a Fully Automatic Starting Device, or FASD. It is a tiny third carburetor strapped to the side of one of the Zeniths, and setting it up is like any other carburetor, except it shuts itself off when the engine is warm. If you use SUs, and I bet most of you do, this function is manual and not a huge deal.

Anyway, as I tune the car, the best method I have found is to go through a full warmup cycle as part of any carb adjustments. This lets me see if the FASD shuts off at the appropriate time (not so much at the moment), if it providing the correct start mixture, etc. Then after a full warm up, I can shut down and read the plugs and tweak the mixture.



Note that it has an electric connection for a fuel heater, two coolant connections to sense engine temperature, a connection to the intake manifold to supply air and fuel, and it is bolted to the side of the Zenith. Very tight quarters makes working on it a source of new and colorful metaphors.

Anyway, slowly making progress. Cold idle seems to be working now, and the hot idle is smoothing out. I must say that the stock Sprint cam is a bit of a bad boy, 270 degrees duration with 109 degree lobe centers makes for an idle with an attitude . Federal cams are glass smooth and rather effeminate.

Well, a few more start cycles and it will be ready for some serious driving. The soft top is tattered and needs replacing as well.

Cheers,

Vance

Interesting stuff Vance! Enjoying your posts, please keep them up.......

Cheers
Keith

There is a reason that the Sprint itself, as well as the TR7 Sprint was not marketed Stateside. The reason being that it turned out to be impractical to "federalize" the 16v motor to an acceptable level, because of that cam duration you mentioned and the fact that the single cam operates both inlet and exhaust valves in a fixed ratio. altering it for federal spec would have meant a complete head redesign and the factory, cash strapped as always, wouldn't or couldn't finance it! Later US spec TR7s had a Lucas fuel injection system to try and ameliorate the difficulties with emissions, but no such system exists for the Sprint motor, which had already been ruled out for US export. A few guys in the UK have imported federal spec TR7 injection manifolds with plans to adapt it to the Sprint motor, i've yet to see a running result so far..........

I was interested to learn of the 3rd carburettor, a new one on me! But could it not be replaced with a simple manual choke? Or do US legislators not trust drivers to push it home once warm? To be honest, nothing would surprise me! I heard a story (which may be apochryphal) about the Spitfire filler cap being moved from the rear deck to the rear wing (fender) on US spec cars (GT6 have it on the wing already) because an American lady used it (top down) as an ashtray with somewhat disastrous results!

However, I don't want to be a prophet of doom and I hope that you can get your project past the testers! It'd be one up on the factory if you do! I think I'd be looking at EFi myself!

Steve

Ive come across those FASDs before... they used to fit them on XJ6s. They are a pain but they can be made to work well, Burlens have all the parts. Not easy to do away with and convert to manual sadly.

Carledo wrote: ↑Wed Mar 04, 2020 8:50 pm I was interested to learn of the 3rd carburettor, a new one on me! But could it not be replaced with a simple manual choke? Or do US legislators not trust drivers to push it home once warm? To be honest, nothing would surprise me!
Steve

Steve:

There are kits available to do the conversion, but I believe they only work on one of the two carbs (the one with the FASD) because the other carb has no provisions for mixture enrichment. I would imagine that the effectiveness on a cold engine is therefore limited and would render the manual conversion a less than happy one. In contrast, the FASD is fed into the crossover tube between the two carbs, and so feeds all four cylinders.

The federal emissions standards eventually required that the cold start enrichment be out of the operator's control. In other words no operator intervention was allowed. So even the US style downdraft choke activation by depressing the accelerator was not allowed. It had to be self activating and self deactivating.

The Zenith water chokes were self deactivating but not self activating - you need to depress the accelerator to turn on the choke. The FASD is controlled solely by coolant temperature as all modern injection systems are.

Moving on to the Sprint engine swap stuff...

To mount the Zeniths to the Sprint intake manifold was easy, both the SU and Zenith use the same 4 stud mounting pattern. However, to preserve the factory look and the federal hot air stove required a bit of ingenuity. I opted to use the back half of the Sprint OEM air box. The SUs use a three bolt air box mounting scheme as do the Zeniths, but the pattern is not quite identical. I could not reuse the TR7 air box back because the center to center distance on the carbs does not match the Sprint's.

By turning the Sprint air box upside down, two of three mounting points align, so it was only necessary to drill an additional hole for each carb to permit mounting the Sprint air box on the Zeniths. Plastic plugs from the hardware store sealed the now superfluous third SU hole. I then drilled a couple extra holes for the hot air stove thermostat (upper right in the photo) and a couple of small holes for the extra air passages that the Zeniths employ but the SUs do not. The extra air passages are for the float bowl vents and deceleration bypass valves.

Everyone deserves a little luck, and the TR7 air box front cover fits the Sprint back with no modifications and allows retention of the intake damper that selects hot or cold air for the intake. The hot air stove supplies warmed air from the exhaust shroud that speeds warmup of the car. When the carbs are fully warmed the damper is moved over to the cold air intake by the thermostat.

I attached a photo of the modified Sprint air box back for your amusement. For those of you still using the stock Sprint air box, look carefully and you will see that the photo does indeed show a Sprint air box.

I have not run the car through emissions testing, but when I do I will post the numbers so you can see why all the extra trouble is needed to run a Sprint motor in the US.

More to come...

Vance

Well, I must have been an axe murderer in a previous life. Karma apparently has come to haunt me.

I installed a new soft top on the TR7 Sprint, and suddenly the weather turned nice. I decided it was time for a real shakedown drive on the Sprint, to see where all the bugs were. I had started the Sprint many times, adjusting the idle, mixture, timing and the FASD for a smooth start and warm up. Time to see what else needs to be tweaked.

Hopped in, made it one block and the oil pressure warning light came on.

I did not believe it for the first 5 seconds. New oil pump, filter, gaskets, fresh oil and I had not seen any problems with oil pressure during the test start ups. Drove 50 yards further and the light did not shut off. Dammit. Turned around and limped home, trailing as it turned out, a steady trickle of oil down the street, up the driveway and into the garage. <mumble>

The culprit was the 40 year old oil pressure sender, which had decided to pack it in, and oil was leaking out around the connector. Now I am waiting for a new sender from my FLAPS. <sigh>

In other news...

Using the Zenith carbs allowed me to reuse the original throttle linkage which is activated by a cable on the TR7. Fussing with the linkage during a test fit, I discovered that the factory linkage did not allow the butterflies to fully open. They only rotated through approximately 3/4 of the 90 degrees needed for wide open throttle. Triumph TR7 owners everywhere should rise up over this little fact. The flaccid federal motor only puts out 95HP to start with, and giving up 1/4 of your throttle travel certainly does not help matters.

With a little creative drilling and filing, I modified the stock linkage to allow a true WOT when the accelerator is fully depressed. I have attached a photo of the modifications. I quickly discovered that it was possible to alter the linkage in such a way that the throttle would stick wide open. Off the side of the road, and through the guard rail we would go...

OK, with that little problem avoided, I got a good result and thought I would share. Dunno if the Dolly uses a similar scheme or not, but it is something people might wish to check on the off chance that this sort of thing is standard practice. It may be only for the US market in an effort to meet emissions or avoid offending our ridiculous tort laws.

In the photos, I added the middle mounting hole for the cable and trimmed the bell crank mechanism to allow more (but not too much!) travel. Note also that there were two factory supplied mounting holes for the linkage rod, and I moved the rod to the otherwise unused hole and plugged the original mounting point with a rivet to prevent future confusion.

Will be posting more whining notes as time goes on...

Vance

Hi Vance, enjoying reading your thread.
I'm glad the oil problem turned out to be a false reading and an easy fix.

The latest karmic episode was pretty interesting.

Have been driving the TR7 sprint to do the usual debugging... Found several issues...

The thermostat must have been bad right out of the box, as the temperature is all over the map, dropping so sharply at times that the fast idle kicks in at stop lights. Pretty sure that means the thermostat is sticking open. Tossed in a new thermostat will give it a drive soon.

One of the sun visors refuses to stay put, easy fix that one...

and... drum roll, please... The fan fell off while I was cruising down one of the local boulevards. I ran over something, and looked in the rear view mirror, and saw what appeared to be a chunk of wood receding in the rear view mirror. Kept going. When I got home I popped the hood to read the plugs, and the fan was MIA.

Turns out there is something called a tolerance ring that fits between the fan and the hub. That let go and the rest is history. Fortunately no damage. I drove back in another car and found it after it had been run over a couple of times. Got a new tolerance ring for $3 USD and tossed it in, fan is back on the car permanently, I hope.

The car is running very rich. I am using stock TR7 needles, which I thought would be too lean. Nope. The plugs are sooty black even on the leanest adjustment possible. Time to reneedle the carbs. The stock SUs use the BCM needle. The stock TR7 uses The B1EP needle. I have opted for the 45P needles from Burlen. There really aren't any needles that match the smooth fueling curve of the SUs, I presume because of emissions. The tendency is for a lean mixture at idle.

I have attached a graph showing the fueling curves based on a 0.100 jet. The curves are plotted based on needle diameter at 0.10 increments along the length of the needle. The scale is inverted to show increasing fuel delivery as the needle is withdrawn from the jet.

The SU needle is a model of smooth incremental fueling. The Zenith needles typically show much leaner idles and then fatten up as the needle is withdrawn from the jet.

Will post the results when I feel the car is running well.

I have had to tweak needles to make them richer in the past, this is the first time I have had to go for a leaner needle after making a change. I have even tossed needles in my drill and given them a couple of squeezes with 400 grit paper to fatten the fuel delivery. Works a treat. Got the TR8 dialed in perfectly this way. But can't do it when I need the mixture to get leaner, so I need the new needles.

Stay tune for more fun...

Vance