Cool run­ning

Classics Monthly - - Staff Diaries -

Ire­cently had a visit from a fel­low TSOAQ com­mit­tee mem­ber to see if we could im­prove the slow run­ning on his Tri­umph Spit­fire. Since ac­quir­ing and com­plet­ing the car he has ex­pe­ri­enced a num­ber of fuel re­lated prob­lems most of which have now been re­solved, how­ever the slow speed run­ning is still an is­sue.

The en­gine op­er­ates well whilst driv­ing at nor­mal speed, how­ever as soon as you try to crawl along in first gear it copies our lo­cal mar­su­pial and starts to ‘kan­ga­roo’ down the road. I thought that the most likely rea­son would be carbs not bal­anced or that in­di­vid­ual but­ter­fly open­ing was not syn­chro­nised so I of­fered to have a look.

We checked all the ob­vi­ous things first, in­clud­ing throt­tle open­ing and float lev­els, which were all cor­rect. We then went through the ba­sic tun­ing op­er­a­tion for a pair of SU’s. Main jets were raised to the bridge then screwed down the rec­om­mended dis­tance and en­gine started so a flow me­ter could be used to bal­ance the air flow through each carb. Mix­ture strength was then ad­justed on each carb and checked by slightly rais­ing each pis­ton, then air­flow rates again checked and but­ter­fly open­ings syn­chro­nised.

The sta­tion­ary en­gine ap­peared to op­er­ate per­fectly but a road test re­vealed the same low-speed prob­lems. Whilst the carbs are worn and could do with an over­haul, in­clud­ing new spin­dles and bushes, we are be­gin­ning to think that the prob­lem is else­where, and that we should now look at the dis­trib­u­tor op­er­a­tion and tim­ing, so an up­grade from points to an elec­tronic sys­tem is on the cards.

This month’s plan was to fit a 77°C ther­mo­stat in place of the stan­dard 82°C unit fit­ted to the Stag af­ter the en­gine re­build. Whilst I had the cool­ing sys­tem par­tially drained I also in­tended to fit a sec­ondary heater water shut-off valve in the en­gine bay. The orig­i­nal heater con­trol valve seemed to have ex­cess clear­ance be­tween the body and plug which al­lows a slight con­stant bleed of hot water to the heater, which may be ac­cept­able in some cli­mates but not here in our tem­per­a­tures.

Also when I fi­nally com­mis­sion the air con­di­tion­ing sys­tem the last thing you need is heat em­a­nat­ing from the heat­ing sec­tion. Also in con­junc­tion with ther­mo­stat re­place­ment the tem­per­a­ture switch for the Ken­lowe elec­tric fan re­quires ad­just­ment to re­duce the time it op­er­ates.

The car was raised on the lift to al­low some water to be drained from the ra­di­a­tor. This was the first use of the lift since re­lo­cat­ing to the new work­shop. When I was hav­ing is­sues with the por­ous water pump cover and sub­se­quent seal­ing of the in­let man­i­fold, I fit­ted drain cocks in place of the drain plugs on the en­gine block to al­low easy water

jacket drainage and these came in use­ful as they al­lowed quick sim­ple par­tial ra­di­a­tor drainage. Ac­cess to the ther­mo­stat hous­ing re­quired re­moval of the air cleaner and I also re­moved the air duct from above the ra­di­a­tor to im­prove ac­cess to the hoses where I in­tended to fit the heater shut-off valve.

As one would ex­pect, all items came apart eas­ily. The three-way con­nec­tion that I had fab­ri­cated dur­ing in­stal­la­tion of the Stag­we­ber header tank was also re­moved. Prior to fit­ting the re­place­ment ther­mo­stat, I took the op­por­tu­nity of check­ing the op­er­a­tion of new and old in a bath of hot water. Boil­ing water was added to a con­tainer and cooled to about 75°C and the two ther­mostats im­mersed. More boil­ing water was then added heat­ing the bath and at 77 °C the new unit opened.

Adding more boil­ing water in­creased the tem­per­a­ture to 82°C but the old one hardly moved and re­quired a fur­ther tem­per­a­ture in­crease to open. I am not sure whether this in­di­cates an is­sue with the old unit or is just pro­duc­tion vari­ance. Af­ter clean­ing up the seal­ing faces on the in­let man­i­fold and a ther­mo­stat hous­ing, the gas­ket was smeared with non-hard­en­ing sealant and used to fit the re­place­ment ther­mo­stat. The two hous­ing re­tain­ing bolts were grad­u­ally tight­ened, then torqued.

The long cop­per pipe leg of the fab­ri­cated Tee junc­tion was short­ened, al­low­ing suf­fi­cient space to al­low fit­ment of the heater valve be­tween this and the stain­less heater pipe us­ing short sec­tions of heater hose and worm drive clips. Af­ter re­plac­ing all hoses and tight­en­ing the clips, the cool­ing sys­tem was re­filled en­sur­ing both heater valves were in the open po­si­tion. Af­ter check­ing for leaks the en­gine was started ini­tially with no ra­di­a­tor cap so I could mon­i­tor the water level. When all ap­peared OK the cap was re­placed and the en­gine al­lowed to warm up again, check­ing for leaks as the water pres­sure built up. Af­ter warm heater pipes con­firmed that water was flow­ing through the heater ma­trix the car was taken on a short test drive. Whereas prior to the ther­mo­stat change the tem­per­a­ture sta­bilised at about 88°C it now ap­peared to be run­ning at 8 or 9° less.

This was only a short test but as it was a warm day, about 37°C I was happy with the out­come. The per­for­mance now needs to be checked un­der vari­able con­di­tions in­clud­ing hill work, and sit­ting in traf­fic af­ter fast open road run­ning.

Those who have fol­lowed the restora­tion may re­mem­ber that I fit­ted a Racetech me­chan­i­cal tem­per­a­ture gauge, so I know I have an ac­cu­rate read­ing of the water ex­it­ing the RH cylin­der head. Af­ter ex­it­ing the cylin­der head the water flows through the in­let man­i­fold where it cools slightly be­fore reach­ing the ther­mo­stat so it is un­der­stand­able that gauge read­ing is a few de­grees above the ther­mo­stat set­ting.

Next month I will re­port on how the car per­formed on fu­ture out­ings. I also need to read­just the head­lights. The lights were orig­i­nally aligned af­ter the car had cov­ered a hand­ful of kilo­me­tres, how­ever when I was out the other evening both main and dip beams were very low.

I sus­pect the change is due to the new springs set­tling but as our new house is in a more ru­ral area with ar­eas of lit­tle or no street lights, good main beams are a pri­or­ity, es­pe­cially as there are Kan­ga­roos in the area that have no road sense and will feed by the road­side around dawn and dusk.

The carbs on my pal’s Spit­fire re­quired tun­ing.

On its way home – im­proved run­ning but not per­fect.

The re­place­ment 77° ther­mo­stat with an ad­di­tional heater valve await­ing in­stal­la­tion.

Re­mov­ing the air fil­ter al­lowed bet­ter ac­cess to the ther­mo­stat hous­ing.

The first use of my ramp af­ter in­stalling it in my new work­shop al­lowed easy ac­cess for ra­di­a­tor water drainage.

Air fil­ter assem­bly re­placed and ready for a test run. The heater valve is not too ob­vi­ous.

Air duct was also re­moved to al­low im­proved ac­cess to the hoses for fit­ting the heater valve. The cop­per pipe re­quired short­en­ing.

Prior to in­stal­la­tion, the op­er­a­tion of new and old ther­mostats was com­pared.

Ther­mo­stat in­stalled and heater valve squeezed into place.

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