westaj
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Posts posted by westaj
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Hi Mal,
The triple carb option doesn't have to be expensive.
For converting my TR250, my starting point was the Goodparts manifold kit from the States and I then sourced some second hand SU carbs from eBay .
I chose SU4 s as used on MGB s rather than SU6s, as I wanted drivability and torque rather than top end power. SU 4 carbs are very easy to obtain.
The engine in my TR250 is an ex- Pi from a saloon car with about 9.5:1 compression and a Newman 280 duration camshaft, and could probably be considered to be in fast road spec.
The SU4s should be able to give around 48 bhp per carb, and for this output, I believe, an airflow rate of around 80 ft/s is expected. Fitting the larger SU6s would drop the airflow to around 58 ft/s, for the same power, which is probably a bit low for good mixing.
(I think from memory some of the 3 litre Austin Healeys were originally fitted with three SU4s, possibly for the same airflow mixing reason)
Due to space constraints and aesthetics I decided to use 3 identical carbs each with right handed (front mounted ) float chambers. The Goodparts manifold inlets are sized at 1-3/4 inch so I fabricated tapering transition pieces to match the 1-1/2 inch size of the SU4 outlet and simple support plates for the throttle linkage control rod.
Lever arms and linkage rods were bought from Burlem Fuel systems.
Choke mechanisms are non standard, but cold starts are fine with just 2 individual choke cables fitted.
The carbs were fitted with FX designation needles, as used on later MGBs, and simply balanced with a flow meter.
Tuning SUs is fairly straightforward and low cost, especially compared to Webers.
The engine runs very well through the full rev range and is smoother and crisper than with the earlier 2 x SU6 setup.
Trips to Classic Le Mans and Laon earlier this year returned over 35 mpg and after an Autumn TR register track day at Castle Coombe, power improvement is estimated to be around 15%. I will need to complete a rolling road test at some point to establish actual power values.
In summary I am very pleased with the simplicity and performance of this triple SU arrangement.
Hope that the above is of some help.
Jerry
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Hi Mal,
The triple carb option doesn't have to be expensive.
For converting my TR250, my starting point was the Goodparts manifold kit from the States and I then sourced some second hand SU carbs from eBay .
I chose SU4 s as used on MGB s rather than SU6s, as I wanted drivability and torque rather than top end power. SU 4 carbs are very easy to obtain.
The engine in my TR250 is an ex- Pi from a saloon car with about 9.5:1 compression and a Newman 280 duration camshaft, and could probably be considered to be in fast road spec.
The SU4s should be able to give around 48 bhp per carb, and for this output, I believe, an airflow rate of around 80 ft/s is expected. Fitting the larger SU6s would drop the airflow to around 58 ft/s, for the same power, which is probably a bit low for good mixing.
(I think from memory some of the 3 litre Austin Healeys were originally fitted with three SU4s, possibly for the same airflow mixing reason)
Due to space constraints and aesthetics I decided to use 3 identical carbs each with right handed (front mounted ) float chambers. The Goodparts manifold inlets are sized at 1-3/4 inch so I fabricated tapering transition pieces to match the 1-1/2 inch size of the SU4 outlet and simple support plates for the throttle linkage control rod.
Lever arms and linkage rods were bought from Burlem Fuel systems.
Choke mechanisms are non standard, but cold starts are fine with just 2 individual choke cables fitted.
The carbs were fitted with FX designation needles, as used on later MGBs, and simply balanced with a flow meter.
Tuning SUs is fairly straightforward and low cost, especially compared to Webers.
The engine runs very well through the full rev range and is smoother and crisper than with the earlier 2 x SU6 setup.
Trips to Classic Le Mans and Laon earlier this year returned over 35 mpg and after an Autumn TR register track day at Castle Coombe, power improvement is estimated to be around 15%. I will need to complete a rolling road test at some point to establish actual power values.
In summary I am very pleased with the simplicity and performance of this triple SU arrangement.
Hope that the above is of some help.
Jerry
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Interesting to read the various suggestions for achieving a good head gasket seal.
In my opinion, for what it's worth, the important factors are the flatness and cleanliness of the 2 mating surfaces. The new/old stud argument is, l believe, of secondary importance due to the link between actual torque applied and the resultant clamping force.
My exPI saloon engine, fitted to a TR250 (with MG XXX engine number and recessed bores), has had no sealing issues or oil staining at block number stamp after 10k miles and 3 years of use.
Initially torqued to 80 ft lb, then re-torqued at 500 miles.
Before retorquing I mark the '12 o'clock' position on each nut with a small dab of white correction fluid.
Using the recommended sequence, the first nut is slackened by about 60 degrees , then 80 ft lbs reapplied. Generally all nuts tighten approximately 30 degrees beyond their 12 o'clock initial position.
Of course every engine is different, but the above worked for me.
Jerry West
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Windscreen Capping advice needed:
I am in the process of fitting a Surrey top conversion on a TR250 and need to change the windscreen capping.
The existing old capping is secured by 9 rivets, at approx 5" spacing.
The new capping (from Moss part 806189), has the forward lip for attaching the front of the soft top vinyl but is drilled with 11 holes at approx 4" spacing.
The new capping also has no provision for attaching the 2 soft top front press studs.
It it possible to buy the correct capping drilled for 9 rivets and with the tabs for press stud provision?
Or, is the solution to either drill the Moss capping with extra holes at approx 5" spacing to match the existing windscreen, or drill the windscreen top to match the 11 hole capping.
Plus, then fabricate tabs with bases to accept the vinyl top press studs.
Any suggestions, from those who have been here before, welcomed!
Thanks
Jerry West
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Hi Peter,
Not sure whether you had a chance to check the piston lift at wot with the method suggested in my earlier note.
I did; both HS6 pistons had fully lifted during a wot test run. I haven't had a rolling road bhp measurement yet, but I suspect around 126 hp with my current set up.
Using your estimated 80 bhp per 2" carb with air velocity of around 75 ft/s ( from the Healey reference in your supertrarged article) and ratio-ing my powers (63 bhp/carb) and areas (1.3 multiplier for HS8 to HS6) gives around 76 ft/s.
As mentioned before, In due course I intend to modify the engine and fit 3 x HS4s.
If the new power approached, say 144 bhp, then each carb delivers 48 bhp.
Ratio-ing the powers (48/80) and areas (1.77 multiplier for HS4) from your Healey estimates, would give a per carb air velocity of 80 ft/s. This would drop to 58 ft/s for 3 x HS6, which, as you cautioned before, is probably too low.
On the Healey forum was a reference to measuring piston lift using a straightened paper clip through the dash pot vent hole. With masking tape the measuring rod (clip) will rise but then, in theory, not fall.
Seems like this maybe be a neater solution rather than using grease on the piston slide!
I haven't had a chance to try it yet and am off to Spa with the London Group tomorrow, so it will have to wait.
Jerry West
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Peter,
I,too,thought that your article was excellent and really enjoyed reading it.
I am thinking of fitting triple SUs to mildly tuned TR 250, mainly because they look nice!
Ideally, three HS4s rather than HS6s, but then I would need to fabricate adaptor plates at the HS4 carb outlets. The topic of piston lift is relevant to the choice of carb size.
A possible way of establishing the max lift at wot could be to smear a small amount of Vaseline or grease on the piston groove at the front of the carb.
You might then be able to establish how far the piston lifted when the engine was fully loaded.
Just a thought.
Jerry West
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Shaun,
I have just fitted new studs to a pair of new drive shafts that I have installed on a TR 250. I drew the stud in initially with nut and spanner, then pressed the stud in further in the vice. On the car then torqued up to 60 ft lbs which pulled them in a tad more. They are well in, although I believe the head chamfer won't allow them to sit fully flush.
As I have got wire wheels, I needed to shorten each stud by a couple of mm to ensure clearance when the wire wheels are fitted.
As part of fitting the new axles, I took the diff out and torqued up the two inner axles, plus changed an oil seal. Both axle nuts were quite loose and with some Dexion restraints managed to tighten these to over 100 ft lbs (they quote 120 in the manual).
Took for a spin around the Surrey lanes this morning; great to have eliminated irritating clunking from the back axle!!
Jerry West
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Roger and Peter W , thank you for your helpful replies.
I suspect the main drive shaft (to the wheel) splines are tight, and that has caused some additionasl loading at the diff side axle bearing.
I get an occasional light clonk coming out of a roundabout. This could be linked to the diff side-axle-shaft free play which I have observed.
When at Goodwood Revival last Sunday, I got talking the the Sales guy at SC Parts (Gatwick). To cut a long story short he sold me a couple of new cv shafts with hubs and these should arrive shortly.
There will be a delay before I can fit these, but I will hopefully be able to examine and replace the side axle diff beatring when fitting the new SC shafts.
I will post more data when I have managed to get everything apart.
Thanks again,
Jerry
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It would be great if the forum could provide some info on the IRS Diff side axles.
When beneath my TR250, I was surprised to note that my near-side driving flange (next to the diff) has about 2 mm of axial free movement. The drive flange is fitted with a taper fit, key and nut to the diff side axle, so the axle is also moving 2 mm.
My questions are:
-is the side axle bearing inner a press fit onto the side axle?
-is there a locating shoulder on the axle for the bearing inner to butt up against?
-in the event of loss of press fit and no locating shoulder and the driving flange disconnected, is it possible to pull the drive flange out complete with inner axle? This would leave the bearing housing, oil seal and axle bearing all in place, with the bearing housing still bolted to the diff.
-or will the bearing inner only fit over the taper end and not the splined end, hence preventing full removal?
Any forum info on this topic would be appreciated.
Thanks
Jerry
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If you have to take the gearbox out for the taper pin (I hope not!) check the sliding surfaces at the release bearing carrier. The carrier slides on the gearbox input cover/snout and sliding clearances will change with temperature. My TR250 (with saloon gearbox) clutch operation was greatly improved; ie. smooth operation with no temperature related hang-ups, after I cleaned up and lightly greased these surfaces.
Jerry
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Hi Jim,
I recommend Phil Irving’s “Tuning for Speed” This is an excellent engine tuning reference book.
Although first written in 1948 and focussing on air-cooled motorcycle racing engines, much of the text is still relerevant today.
I have the 1956 3rd edition; I think it went to the 5th edition in 1969.
In the 60 ties Irving was employed by Jack Brabham to design engines for Brabham’s FI racing cars; from the recent stuff in the press, I think Brabham won with the Irving designed engine in 1966.
Specialist bookshops will sell copies for around £100, but 2nd hand copies are readily avaiable at Autojumbles for around £10.
Hope this helps………………Jerry
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Dave,
I have a TR250 fitted with an A type overdrive from a 2500 saloon.
The o/d number is 22/61973/017142. I understand that, the 22 is the o/d % speed ratio; 61973 refers to a 2.5 PI Saloon 1968-1972. Final numbers are the Serial No.
Whereas I believe A 22/61971/etc refers to a TR5 or TR250 unit.
My ex-saloon unit is fits fine and has the original horizontal solenoid, I think that you can convert them to vertical at some cost. The rear o/d unit mounting is different and needs some simple mounting modification.
With my 185/80/15 tyres, the speedo over reads slightly and I will correct in due course by modification at the instrument.
Hope this helps.
Jerry
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You could drive the car in top and check the engine rpm reading against the speedo reading; there'll be a direct relationship depending on your back axle ratio and wheel size.
You might won't to also check the speedo accuracy; drive at a steady indicated 60 over a measured mile and record the time.
Just a thought; I'd be interested in the results.
Jerry
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Plus, from memory, Jaguar's early XK engines, where number one cylinder is inboard..............Jerry
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To check the old and new spring-rates, set up the old and new springs is series in a vice separated with a small plate and measure the 2 lengths.The force on each spring is equal and the reduced lengths can be measured. The weak spring has the shorter length. I would be interested in the results. I didn't bother with new springs on my current rebuild as its unlikely that I'll be spinning my 6 cylinder engine much over 4,500 rpm. Jerry
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You could consider fitting a digital thermometer/clock. Lidl are selling a neat unit in black (approx 5” x 1”) which displays inside temperature, outside temperature and time, simultaneously. I bought one for the ambient air sensor. This, the outside air temperature sensor, is a small device at the end of 3 metre of cable, so it can be located at grille area. Also has an ice warning bleeper, which is handy if you drive the TR in the winter. The units were selling for £3:49, which is less than a pint of beer in Surrey! Jerry
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Thanks Steve, i have always been under the impression that the quality of County parts was pretty good, so was suprised to see them with the low cost numbers!
A quick search for bearings showed Mains for £53 if Glacier or £28 County, and Rods with Glyco at £56 and County £28.
My preference is to obtain quality bearing shells; with cost, presently, of secondary importance.
Jerry
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I am part way through rebuilding a 6 cylinder PI engine and now need to buy some standard sized mains and big end bearing shells.
For mains, suppliers offered are Glacier and County and for the rods Glyco and County.
For both, County are approximately half the cost of the alternative.
It would be great if members could advise of any good or bad experiences with these different bearing Suppliers.
Thanks
Jerry
Triple Webers or PI?
in TR6 Forum
Posted
Hi Niall,
Picture of my 3 x SU4s arrangement attached.
I have no issues with the Triumph engine firing order and its uneven stagnation periods, ie. with 1,2 and 5,6 on uneven pulses and 3,4 on even.
There is some intake balancing across the 3 carburetters, achieved by interconnecting the 3 low pressure connection ports just upstream of the throttle plates to the rocker box breather. I believe that this lowers the pressure in the engine which helps to minimise oil leaks.
For about 95%+ of my driving I am not at full throttle, so the 3 x 1-1/2 inch set up provides sprightly performance, simplicity and good economy.
Hope the picture helps.
Jerry