TR250 Technical Tips

I think I have picked up a few useful things in the rebuild of this car but obviously I am not a professional so please take these tips with a pinch of salt!


1.How I get the engine in
3.Compression ratio
4.Valve stem oil seals
5.Oil pressure and oil cooler

Fuel Exhaust and Ignition

1.Oxygen sensor
2.Making the Carb's adjustable
4.SU carbs
5.Sports Manifold
6.So you want to go PI?

Clutch Gearbox and final drive

1.Converting to Overdrive
2.Toyota Clutch release bearing
3.Reducing spline lock.

Bodywork and suspension

1.Suspension tweaks
3.Windscreen wiper
4.Do you keep getting flat tyres?

Solo Engine Replacement

Firstly don't be afraid you CAN get this engine in all on your ownsome.
I assembled the engine out of the car but didn't install the starter, alternator or distributor, but do work out what gaskets you will need for the distributor driveshaft's clearance. Install the manifolds now, its much easier but dont forget to mount the front lifting eye first otherwise one bolt is covered by the manifold. Then install the gearbox, I use a LONG stud (actually one of the ones which hold the rocker cover nuts) or you could cut the head off of a long bolt and put in place of the top stud in the engine block. This prevents the splined shaft engaging at exactly the same time as the studs which makes it difficult. Once the gearbox is on replace the original stud. Now is the time to fit the water pipe between the pump and rear of the engine, it mounts to the gearbox and is a pig to adjust once in the car

Assemble the engine mounts to the brackets and put them aside, same with the gearbox mount, bolt it to the crosspiece and put it aside. Next unbolt the steering rack, leave the tie rods connected. You can get by with this in place but its worth the time taken. Undo the steeering column at the rack and tie it up on the wire loom on the wheel arch then pull the rack forward a few inches. Position the engine over the bay and tilt it to about 50 degrees, you must have a reliable way to tilt the engine or you will be fighting it forever, I use a "comealong" at the front to hold it at an angle. Then just feed the engine in, untilting it slowly. The bellhousing will just clear the exhaust downpipe (thats why you left the starter off) then you can get the engine right in till its about 6 inches from position, This is where moving the steering rack helps if it was still in place you cant have the engine horizontal yet and you get problems at the gearbox end. By this time I have the comealong to the rear of the engine to hold the gearbox end up a little so just check all is well at the propshaft area and shove it back the last few inches making sure the exhaust pipe is clearing the manifold. Dont worry there is enough flex to get the gasket in later.

In the words of Arkwright the greengrocer in the British sitcom Open All Hours "just j-j-j-jiggle it a bit" and you can get the 4 bolts for the engine mount brackets started and the 2 nuts & bolts for the mount to chassis started on each side, don't tighten any till they are all in place. Then the gearbox mount can be slotted in, you may have to raise the box a bit. 4 nuts and bolts to mount it to the chassis and 2 large ones for the box to mount, leave the exhaust bracket till the manifold is connected. Its in! Tighten all the mounting bolts now, later on they will be harder to get at.

I then sort out the exhaust downpipe to manifold joint, then work round the engine from rear left (starter)to rear right (fuel pump) then replace the rack and steering column before fitting the crossbrace. I always forget to install the fan before the radiator so do that now.
the rest is easy!


I can only really talk about the camshaft I used. this was the 35-65 cam from a TR5. I think the biggest mistake is to overcam your car and be left with something which will not pull at the low end and peaks at such high revs that you are scared to use it. So I settled on the TR5 cam as a Known quantity, I am VERY pleased with it, it pulls well at all revs and most noticable is that it keeps on pulling until you hit the red line and above. I expected a bad idle but its fine. If you go for a hot cam make sure that the rest of the engine is ready for it, compression needs to go up, the head will need porting & flowing and you WILL be pushing it harder so get the engine balanced. Of course no cam will perform fully without better carburettion and exhaust flow (If you run out of money these can be "bolted on" later)
As to timing it, I was succesful with a timing disk and dial guage. The thing to get in you head is just what the cam timing means. This Diagram helped me. You will notice that the camshaft sprocket has 4 holes, legend is that they are slightly off of 90 degrees to each other so if you are having trouble getting the timing right try the other pair of holes, this worked for me but I suspect all replacements are not this way.
I skimmed 30 thou off my head, with this and the camshaft change the pushrods were much too long. Thats OK as there are 3 lengths of pushrod out there, I used some from a GT6 engine.

Compression Ratio

Compression ratio can be adjusted by skimming the head and or the deck. Here is how to work it out, staying in metric measure helps. First you need your swept volume (sv). Thats the volume between the piston being at the bottom to the top. Find your bore size (dont forget any rebore), half it to get radius, find the stroke and use your 8th?? grade math (pye r squared times height) to arrive at the volume. mine was

44.73(area) X 9.5 (stroke)=424.95cc(sv)

Next you need the combustion chamber volume (cv) this is the volume above the piston in the bore, the volume in the gasket and the volume in the head. 4.6cc is a good guess for the deck and gasket but if you suspect the block has been decked then you had better measure it! use a dial guage to determine the difference between the piston top at tdc and the deck then multiply it by the area of the bore (pye r squared again). This can be negative!! i.e the piston can go above the deck (like mine!) the gasket has to be guessed, my guess was 0.75mm thickness. You now need to find the chamber volume. The only way to do this is to "cc" it which involves sealing it off with a plexi plate and filling it up with a liquid from a calibrated measure to see how much it takes. Best buy a book for that!! Initially mine came out at 50cc.
So here are my initial measurements:-

(-0.018cm deck, 0.075cm gasket) or 0.057 X 44.73(area) gives 2.55cc plus 50cc(head) gives a total of 52.55cc(cv)

(sv/cv)+1= compression ratio
so I have 424.95/52.55=8.08 add the 1 and its 9.08 that is my compression ratio. You may ask, why is it 9, this engine is supposed to be 8.5?? well the bores were +30 that increases sv, and the block was decked which reduced the cv. both will increase the Compression. I decided to get the head down 3cc so had 30thou skimmed off (10 thou per cc is a good bet) now its 424.95/49.55 =8.57 plus1 gives 9.57. End of maths lesson!

By the way I am told (by my fellow Brits) that American fuel is crap...This is Rubbish. The UK uses RON as an octane measure, USA uses RON+RMN/2 as RMN is a tougher test it forces the octane rating down eg RON=98 RMN=88 this gives 93 octane in USA 98 in UK So American Gas is great!!

Valve stem oil seals

Why not? Most other engines have them, but for some reason (probably because no oil gets to the rocker shaft!) Triumph did not. My Machine shop found some that fit and they work fine. Also if you have a rocker shaft feed pipe (as you should!) you will definately need them as it will flood the valve stems with oil. I recently replaced my valve springs using compressed air to hold the valves shut and it went well, the job took less than 2 hours so go for it.

Oil pressure and oil cooler

Again all I can really say here is what I got after the engine rebuild. I get 80psi or so at highway speeds and 40 or so at Idle. An oil cooler will reduce the cold pressure slightly but an uprated bypass spring restores it (at least at the top end) The main thing an oil cooler does is stop the oil getting too hot and dropping the oil pressure even more, especially when you are thumping it down the Interstate.

Oxygen Sensor

This is worth the effort! All you need is a sensor ($30) a nut to screw it into and a decent test meter. There are a few types of sensor ranging from "1wire" to "4 wire" they are all basicaly the same. The difference is weather they have a heater or not and/or if the ground is on a seperate wire. 1 wires (no heater) have to be placed near enough to the engine to get hot enough to work. So all you do is get the Nut welded in at the right place(es) Ideal is to have one reading each carb, otherwise you need to establish that the carbs are set up exactly the same and adjust both equally from there. This Picture shows where I installed mine on the sports manifolds. To read the output connect a meter between the wire and the body of the sensor. I ran a shielded cable into the glovebox for this, using a small hoseclamp to make the connection to the body of the sensor.
What you will get is a voltage between 0.05 and 1.0 volts This is a direct reading of the mixture. Here is a chart.

Voltage Lambda Ratio Fuel/Air Ratio Comment
0.050 1.25 18:1 Lean misfire limit, I assure you it misfires here!
0.100 1.07 15:1 Max. MPG point
0.400 1.0 14:1 Stoichiometric
0.870 0.9 12.6:1 Max. power point
0.920 0.8 11:1 Over-rich
1.000 0.7 10:1 Rich misfire limit

The idea here is to get the value at 0.4 volts or less for cruise (but not below 0.1), 0.87volts for acceleration and 0.45 volts for idle. As you can see this is testing the whole needle profile, not just the idle part. So you can get the best needle for your engine. The sensitivity is really high between 0.1volt and 0.8 volt so you are unlikely to see them steadily but more likely it will bounce between these values. My original strombergs were not adjustable so I converted them and in the end I settled on a TR6 needle. If you are really into it try polishing the needle to change the profile. My plugs have those lovely "brownish" deposits now so all is well

Having said all that 15 or more years ago, I would now look into a wideband O2 sensor as the prices are reasonable these days

Making your Carbs adjustable

Early Strombergs were not adjustable. The easy way is to lay your hands on a pair of pistons from a later carb which has adjustable needles. On mine the jets used to be adjustable but were cut off and sealed. Its hard to describe but I threaded the body and fitted a brake line nut and extended the jet adjuster through it. Now if I screw the brake line nut into the carb the jet goes up, screw it out and it goes down. Sorry but thats the best I can do to describe it!

Converting to SU carbs

I managed to get my hands on a pair of HS6SU's from a Volvo. Installation was easy once I worked out the linkage. In the end I reversed them, (i.e. front to back) so that the shafts were on the inside, and extended the shafts by drilling and locknutting some old shafts on so that the original linkage could be used, see the picture. I got hold of a great SU book "How to power tune your SU carbs" by Des Hammill (see also Ignition) which describes in detail just how to contour your own needles. I have not got round to that yet but have found that SM needles are pretty near right. In the end the car pulls better, starts better and just feels great. At the emissions test it JUST failed in full tune with 3% Co, 1030 Hc (limits are 9%Co, 950 Hc) My understanding of Hc is that it is unburnt fuel so retarding the ignition means the carbs have to be opened up more to idle at the right speed. The extra air "flushes" the Hc (unburnt fuel) through a little better. A retest got it through easily. By the way the SU book says that ANY well tuned carb should produce 2-3% Co.


Get electronic ignition, the spark is much better and I was able to open the plugs out to 0.35. I used a Pertronix module which sits inside the distributer and works well for around $75. It also eliminates any problems caused by a worn distributer shaft. I also fitted a Lucas Sports coil. The spark is now HUGE. The distibutor on American cars has a lot of advance (28deg on a TR250) this is too much for a tuned engine. I got my hands on a TR5 one which has 12 degrees If you go that way watch the dog at the end of the shaft, in mine the hole for the pin was drilled at a slightly different place which makes it LONGER than a TR6 distributor which would not reach down far enough to engage the gear!!. I guess the pedistal is different on my TR250 and using a TR6 pedistal as well would correct it. I talked about this to some mechanics and they said I was crazy but I assure you mine was different. In the end I was not happy with the TR5 distributor. Enter another great book by Des Hammill, "How to power tune Ignition systems" (see also SU carbs)This indicated that for my engine I needed about 22 degrees total advance. I adjusted the advance by filing the stop I made it 22 degrees and I am now happy. I got rid of the retard module a long time ago, It only works when the throttle is closed and anyway the little valve is not available. Just set the timing at 10degrees btdc and adjust the carb for 850 rpm.

Sports Manifold

I fitted a Tubular 3 into 2 manifold from Moss. The first problem was it fouling the inlet manifold, Careful "Dinging and grinding" made it fit but I was not impressed with that. Then I was dissapointed with the amount of noise it makes, I forgot that it would be noisy and was not willing to accept that much noise It spoiled the "tone" and thats my favorite part! Off it came and I wrapped it in manifold wrap which quietened it down to an acceptable level. It does seem to make a difference, though I did install the SU's at the same time. It pulls better in mid range which feels good. I am now around 9.5 secs 0-60 and sounding good!

Converting to PI

I have not done this but have had a few e-mails on the subject. The first thing to note is that pre 72 USA engines have different spacing on the inlet ports so the UK PI manifolds do not line up properly. Post 72 USA engines have the right spacing but smaller exhaust valves. Then all you need is the camshaft (including double timing chain if not already fitted), Compression ratio up to 9.5, Distributor with 12deg advance and twin exhaust system. Find a PI system, convert it to lead free and Bob's your mothers brother!!

Converting to Overdrive

This can be done, the only difference is the mainshaft and the cover which has switches mounted. "A" type mainshafts are not available so you will probably have to buy the complete box anyway. This is what I did, I used the best parts from both to make a good box up. "J" types are a better bet as Volvo still sell parts for these and the mainshaft is available. Use LOTS of grease on the thrust washers when installing the leyshaft!

Toyota Clutch release Bearing

For a while now the Clutch release bearing supplied for the TR has been lousy. Mine failed within about 2000 miles. There is a release bearing from a Toyota Land Cruiser which is almost the same. The holder just needs to be turned down a little. Phone around your suppliers (BRG, phone 302-368-1117 has them) and someone will have one with holder ready to fit. Mine is working fine.

Spline Lock

Spline lock is when you come out of a corner at full throttle and the splines in the rear driveshafts bind. This holds the rear suspension in a compressed condition until you lift off the throttle, when you feel the suspension jump to its normal position, its wierd! I was told to repack the splines in a good quality Molly Grease. This does help.

Suspension tweaks

I have done a bit here, first was a front anti roll bar, next was nylatron bushings all round and then I went for uprated rear springs and standard front springs. I had a little too much negative camber at the front left (about 3deg) and worried about this for a long time. I could feel it in right hand corners. Eventually I came up with an idea and put some shims between the crosspiece and the suspension turret where it bolts on, reasoning that the crosspiece determines how much the top sticks out. There is plenty of room when you jack it in the middle and 2 shims got me back to 1 degree. I am pleased with the result, The car was well balanced, but comfortable. The biggest improvement was with the uprated rear springs. Before it always wanted to oversteer and I had to be careful, now when it breaks away it simply drifts. Recently I installed SPAX adjustable shocks at the front which improved things but then a rear anti roll bar and tubular shocks at the back did not impress me. I think the rear shocks with the kit were too stiff and although it handles better it is very uncomfortable. I am also finding that once you hit the limits it gets nasty, well nastier than it used to, after all we are talking TR here!It also may be that I am going harder into the corner now. Anyway I am ordering some SPAX adjustables for the rear to try to make it more comfortable and perhaps a little better behaved at the limit. I went to wider tyres. I chose 195/65 x15 Dunlop D60s because they are the same size as the old 165's I had and found that 24psi front, 26psi rear works well but with the new shocks I am still searching for the pressures. Redlines?? I hate them!! I think they look ugly especially on the TR4/5, even more so with wire wheels. For anyone who actually drives their car 4 modern tyres look and perform far better and cost about the same as 1 redline baloon, think about it.


Quite a few people ask about my paint. Its Royal Blue, which was a direct match for Chrysler "Nightwatch Blue" (1981/2) I used PPG paints, DP epoxy primer This stuff is great, seals off rust and nothing gets through it, 8 years on and I have not seen a single pop or blister. A standard hi build primer/surfacer went on next which was sanded down and recoated until the surface was level. Using red DP and grey Primer told me when to stop sanding!. Then a sealer coat of DP went on. The colour basecoat coat was DBU Deltron 2 -3 coats. Its real easy to spray, but make sure you have plenty of light to check for "thin" areas. Finally 2-3 coats of DCU 2020 Clearcoat. This also went on fine but I should have used an accelerator as the dry time was a little too long and not being in a paint shop, dust (and flying ants) are always a factor.

Windscreen Wiper

This only applies to TR4A TR250 with the square 2 speed motor. I rebuilt a couple of these and was confused because they did not seem to work properly. Looking at the Car wiring diagram it seems simple, power is supplied to the motor and ground to the switch. switching to fast or slow puts ground on one or other of the wires. The trouble was every motor I looked at didn't work this way, Power is on the green wire and if you ground the red it goes fast if you ground the yellow wire nothing happens. The only way I could get a slow speed was to ground BOTH the wires together. I talked to 3 other people at a show and none had 2 speeds working, Strange! In the end I pulled the "Clear Hooters" switch apart, all was revealed. The center connector is connected to ground, if you switch it one way one of the connectors gets shorted to center. If you switch it the other way there is an extra contact (in my case bent back and not working) which would make BOTH connectors short to center. Once I bent it around a bit the motor ran at 2 speeds. I suspect this is a common failure of this switch. I also wonder if replacement switches are correct and short BOTH contacts to center in the slow position?

Keep Geting Flat Tyres??

I recently replaced my wheels and tyres, I went to 195/65 Dunlops on 72 spoke wheels. Within 2 weeks I had 2 flat tyres. What Jim at BRG found is that on some new tyres there are 2 or 3 small stickers on the inside and the glue seems to eat away at the inner tube. He says that this is the second time he has seen this, last time it was not Dunlops so it seems that you have to watch them all. You can see by the marks on the inner tube where the stickers were and both had the leaks from those marks so My advice is REMOVE ALL INTERNAL STICKERS and any traces of glue.

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