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Advice On Pistons and Engine Rebuild


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Hello

 

In my continuing battle against my wreck of a TR4A, I've reached the engine rebuild and I wanted to see the opinion of people with a lot more experience then me.

 

I believe the TR4 engine comes with 86 mm liners/pistons. Is there any advantage to going for a wider bore, the most common seem to be 87 mm or 89 mm?

 

Also if I wanted to put in an 89 mm set, what other things will I need to consider? Would I have to make sure the original engine bores are the stanadered size? Would these have ever been bored out (without the wet liners)?

 

I know that you can buy the different sets from Rimmer Bros and Moss, what are peoples opinions of these? Are there better places to get them from?

 

Any advice would be greatly appriciated.

 

Thanks

 

Adam

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Hi Adam,

 

 

No the block will be bored a standard size in the spigots (the bored "part height" holes in the bottom of the block casting which accept the interchangeable liners) unless there's been a racer involved making mods where there could be any number of strange concoctions practised upon the block (and head).

 

The fitment of the 87 and 89mm piston and liners sets will give greater power (variable amounts depending upon the fitment of other components, the TR engine doesn't easily give hp until you get the whole set of variables correct then it will give an enormous chunk. There's not many classic engines which will give a 100% increase in power with reliability.) There will also be a commensurate increase in torque which the TR engine being relatively long stroked gives good figures in.

I would encourage you to develop the engine more with torque in mind rather than b@lls out power. More power can best be used with more revs but it gets wearing driving public roads a gear below where the engine should be to keep the plugs clean and avoid it bogging down. If trickling along in overdrive top at 50 mph or less is your bag (and why not) then the 89mm piston and liner sets will get you part way there easily and with reliability.

As to which pistons are best I believe almost all the specialists sell County and A P Hepolite piston sets which give good results unless you want to lay out for a set of forged pistons which will cope with competition also.

Regarding the 89mm modification if you wished to get the best power/torque available take note from my comments above and decide how far you wish to go. A fast road spec which will tick all your boxes is amongst the hardest engine to build, a "weapons grade" unit with no compromises and an expected life of 20 races before being "refreshed" amongst the easiest.

 

Mick Richards

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Adam,

 

In my view, stick standard...you want a reliable and valuable car, and that's the one which is the result of the engineering which Triumph did over 20+ years. These combinations of bore/cam/exhaust etc give the original fun performance for which the car is renowned. If you want a faster car, buy faster car.

 

The danger with upgrades is the spiral of changes which rarely leads to a reliable result...bigger pistons need better breathing to perform, wild cams don't idle well, big exhausts are obtrusive, crazy carbs & injection make the car a mongrel. All of this stresses the cooling...and of course fuel economy disappears.

 

let the flaming begin,

 

dave

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Hi Adam,No the block will be bored a standard size in the spigots (the bored "part height" holes in the bottom of the block casting which accept the interchangeable liners) unless there's been a racer involved making mods where there could be any number of strange concoctions practised upon the block (and head).The fitment of the 87 and 89mm piston and liners sets will give greater power (variable amounts depending upon the fitment of other components, the TR engine doesn't easily give hp until you get the whole set of variables correct then it will give an enormous chunk. There's not many classic engines which will give a 100% increase in power with reliability.) There will also be a commensurate increase in torque which the TR engine being relatively long stroked gives good figures in.I would encourage you to develop the engine more with torque in mind rather than b@lls out power. More power can best be used with more revs but it gets wearing driving public roads a gear below where the engine should be to keep the plugs clean and avoid it bogging down. If trickling along in overdrive top at 50 mph or less is your bag (and why not) then the 89mm piston and liner sets will get you part way there easily and with reliability.As to which pistons are best I believe almost all the specialists sell County and A P Hepolite piston sets which give good results unless you want to lay out for a set of forged pistons which will cope with competition also.Regarding the 89mm modification if you wished to get the best power/torque available take note from my comments above and decide how far you wish to go. A fast road spec which will tick all your boxes is amongst the hardest engine to build, a "weapons grade" unit with no compromises and an expected life of 20 races before being "refreshed" amongst the easiest.Mick Richards

Hi Mick,

I assume you mean a 100% increase from when it was a tractor engine! I understand a standard TR4 engine should give around 100 bhp @ the flywheel (say 75 bhp @ the wheels?) so what bhp would you reasonably expect with the kind of mods you have in mind?

I have a Racetorations built engine with decked 87mm pistons, fast road cam, balanced crank/flywheel etc, stainless 4 branch manifold & exhaust, twin 45 DCOE Webers jetted to suit on a matched inlet manifold & I am getting 114 bhp @ the wheels (say 140 @ flywheel).

Not sure what was done to the cylinder head but would assume it was improved a little by Racetorations. Would have hoped for a little more with that setup but power comes in nice & smooth @ around 2000 rpm. Tick over is good & I get around 24 mpg.

What could I easily do now, to up the bhp a bit?

Cheers.

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Monty - what you have is a very usable fast road car.

If you start to do more to the beast it will

(a) cost a disproportionate amount of money

(B) make it a less usable road car (but a better competition car).

 

You are getting the sort of performance, power, consumption which I have in 4VC - and it's fun! And it's reliable.

 

If you want to increase the power, it's likely that you'll be wanting and allowing the engine to run to higher speeds, so you may want to install a steel billet crank, Carillo rods etc, and then you'll want to change the rear axle ratio to 4.1 or 4.3 (or even 4.55) to give greater acceleration.

It ceases to be a road car and is less pleasurable to drive on the road, especially on motorways (and one has to use motorways sometimes!).

 

Enjoy what you have - it may not match the very hot hatches (or the big turbo diesel SUVs and estates), but it will give you great pleasure.

 

Ian Cornish

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Monty - what you have is a very usable fast road car.

If you start to do more to the beast it will

(a) cost a disproportionate amount of money

(B) make it a less usable road car (but a better competition car).

 

You are getting the sort of performance, power, consumption which I have in 4VC - and it's fun! And it's reliable.

 

If you want to increase the power, it's likely that you'll be wanting and allowing the engine to run to higher speeds, so you may want to install a steel billet crank, Carillo rods etc, and then you'll want to change the rear axle ratio to 4.1 or 4.3 (or even 4.55) to give greater acceleration.

It ceases to be a road car and is less pleasurable to drive on the road, especially on motorways (and one has to use motorways sometimes!).

 

Enjoy what you have - it may not match the very hot hatches (or the big turbo diesel SUVs and estates), but it will give you great pleasure.

 

Ian Cornish

You are always a stabilising influence Ian! Yes, my car is all those things you have said but then I see better figures quoted for other cars of similar specification & I start to wonder......! Maybe others are exaggerating?

Cheers.

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TR Shop did have a good offer on piston and liner sets, may be still on.

 

I have nothing to do with the TR Shop, just a satisfied customer.

 

Good luck, David

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Monty,

 

Quite right, any figures given are purely reflective of the rolling road/dyno and the operator and atmospheric pressures at the time. I always judge cars and their supposed HP against their places and results in competition, so why bother what your engine is supposed to make ? If it's snappy and good to drive especially if it can give you those things on the public roads without complaint then it's good.

 

As to what could you do easily to up BHP now...nothing, because nothing comes easily or cheap especially releasing HP from engines. The trick is to build an engine that gives you the performance you want and still be nice on the roads, and from what you say you're happy with what you have.

 

I never claimed 200hp at the rear wheels from my engines that I built and won the TR Register Race championship with in 87and 88 and built the 89 Race Championship winning engine for my car I sold on to allow me to compete in a TR7 V8 in subsequent years . But we beat those that did.

 

1987 TR Register Race Championship winner - Running in tuned class and complying with it's restrictions, 88.9mm Rover V8 pistons on 1 3/4 SUs - 132HP Rear wheels.

1988 TR Register Race Championship winner - Running in tuned class and complying with it's restrictions, 89mm forged pistons on 1 3/4 SUs - 148HP Rear wheels. Same engine in Relay races using 45mm Webbers 165hp Rear wheels

1989 Engine builder of TR Register Race Championship winning car, Running in tuned class and complying with it's restrictions 89mm forged pistons on 1 3/4 SUs - 152hp Rear wheels.

 

The figures mean nothing, it's how the car puts it down that counts.

 

Mick Richards

 

PS:...Oh forgot, engine was on standard crank and conrods.

Edited by Motorsport Mickey
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Thanks all for the replies.

 

In all honesty, I do see your point Dave and actually there is part of me that agrees with you. However, I don't see much wrong with trying to squeeze a bit more power out of the engine. In my mind I thought the 87 mm piston and liner set would be a good compromise. The one thing I am upgrading is the distributor and ignition coil to a Lumanition Optotronic system, after researching this, it seems you will get a huge gain from simply improving the spark.

 

Adam

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To my mind, the simplest approach would be to go straight to 89mm piston/liners.... I'd expect that to give the best foundation for anything else you may want to do later.

...... Andy

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My car has an engine with 88mm liners (that's what were available in 1992), incorporating all the ideas that can be found in Kastner's Preparation Handbook. The car has been on the road since 1993 and in 2009 the North London Group took some 20 cars to Enginuity's rolling road. Mike North had his "tribute Rally TR4", which had been built by Manvers at the same time as Jonathan Hancox's 7VC. The torque and power figures for my and Mike's car were almost identical up to 5200 rpm (Enginuity were kind and didn't want to blow up any one's car!). I was pleased because 4VC.had not had any setting up since 1996 (and still hasn't!), but it does have electronic ignition (Newtronic Piranha), so this never needs to be adjusted. I can't say whether electronic ignition liberates more power since the kit was installed when the car was re-built by Neil in 1990-1993, but I am sure it gives a fatter spark when cranking. Of course, 4-pot TRs on SUs are always easy to start.

Ian Cornish

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My car has an engine with 88mm liners (that's what were available in 1992), incorporating all the ideas that can be found in Kastner's Preparation Handbook. The car has been on the road since 1993 and in 2009 the North London Group took some 20 cars to Enginuity's rolling road. Mike North had his "tribute Rally TR4", which had been built by Manvers at the same time as Jonathan Hancox's 7VC. The torque and power figures for my and Mike's car were almost identical up to 5200 rpm (Enginuity were kind and didn't want to blow up any one's car!). I was pleased because 4VC.had not had any setting up since 1996 (and still hasn't!), but it does have electronic ignition (Newtronic Piranha), so this never needs to be adjusted. I can't say whether electronic ignition liberates more power since the kit was installed when the car was re-built by Neil in 1990-1993, but I am sure it gives a fatter spark when cranking. Of course, 4-pot TRs on SUs are always easy to start.

Ian Cornish

Ian,

I believe Mike was on SUs in 2009 so it is interesting (& a little frustrating) that my Webers apparently give no more bhp than his car then & your 4VC!

Cheers.

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I believe Mike was on SUs in 2009 so it is interesting (& a little frustrating) that my Webers apparently give no more bhp than his car then & your 4VC!

 

 

OK putting my flame suit on but

 

Why would you expect a carb set up that at best can only hold perfect mixtures at about 3 bands in the rev range to be better than an analogue set up that can if done properly provide a perfect mixture over the entire rev range?

 

running for the bunker

 

Alan

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Adam - pop up to TRGB and I'll take you for a spin in my recently fitted new engined 4a. All I can say is that this new engine is superb and made even better by twin 45 Webers. Jason at TRGB is their engine builder and he's very fastidious.

 

My spec is std crank, 89mm, fast road cam, gas flowed head, balanced internals, lightweight flywheel, etc etc and with the Webers on it not only goes well it starts, ticks over and generally behaves itself in all situations. I was going to go with a full billet crank engine but decided to keep the bottom end standard in the end and I'm pleased I did. My Webers were fettled by Mass and the improvement was eye opening.

 

Best if you can actually experience what you get with your choices. Many here will say SU's are adequate and indeed they are (I ran them for 6 years) but twin 45 Webers adds a whole new dimension to the car and the soundtrack too.

 

You'll need to invest in suspension, brakes, tyres etc etc too if you want to make the most of the extra horses I'd say.

Edited by Mark1965TR4aBRG
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Adam - pop up to TRGB and I'll take you for a spin in my recently fitted new engined 4a. All I can say is that this new engine is superb and made even better by twin 45 Webers. Jason at TRGB is their engine builder and he's very fastidious.

My spec is std crank, 89mm, fast road cam, gas flowed head, balanced internals, lightweight flywheel, etc etc and with the Webers on it not only goes well it starts, ticks over and generally behaves itself in all situations. I was going to go with a full billet crank engine but decided to keep the bottom end standard in the end and I'm pleased I did. My Webers were fettled by Mass and the improvement was eye opening.

Best if you can actually experience what you get with your choices. Many here will say SU's are adequate and indeed they are (I ran them for 6 years) but twin 45 Webers adds a whole new dimension to the car and the soundtrack too.

You'll need to invest in suspension, brakes, tyres etc etc too if you want to make the most of the extra horses I'd say.

Hi Mark,

Do you have any bhp figures (@ the wheels) for your new excellent sounding engine?

Cheers,

Mr Curious.

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OK putting my flame suit on but

 

Why would you expect a carb set up that at best can only hold perfect mixtures at about 3 bands in the rev range to be better than an analogue set up that can if done properly provide a perfect mixture over the entire rev range?

 

running for the bunker

 

Alan

Several people appear to be using Webers successfully & my engine runs smoothly throughout the range, tick over is even & mpg good. I also have a 4A with pretty well the same engine spec except it has SUs & it produces around 14 bhp less than the Weber equipped car. Just thought it would be a little more.

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"89mm forged pistons on 1 3/4 SUs - 148HP Rear wheels. Same engine in Relay races using 45mm Webbers 165hp Rear wheels"

 

And that's modifying the engine for full race and accepting that it would have limitations if I was so foolish to try using that engine on the road. The SUs would have similar limitations on road use with that engine, but showing this is to try to illustrate that fitting Webbers does not give you gobs of power, it's the engine mods you do that allows the carbs to give that power in conjunction with the modifications.

You would do well to modify your engine to exceed the power gain of about 15hp for Webbers on an 89mm engine, so your figures of 14hp less for SUs are not too shabby, it's just the totals where it would need work.

 

Everybody has an opinion it's just that...PM me if you wish to discuss.

 

Mick Richards

Edited by Motorsport Mickey
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"89mm forged pistons on 1 3/4 SUs - 148HP Rear wheels Relay races using 45mm Webbers 165hp Rear wheels"

 

And that's modifying the engine for full race and accepting that it would have limitations if I was so foolish to try using that engine on the road. The SUs would have similar limitations on road use with that engine, but showing this is to try to illustrate that fitting Webbers does not give you gobs of power, it's the engine mods you do that allows the carbs to give that power in conjunction with the modifications.

You would do well to modify your engine to exceed the power gain of about 15hp for Webbers on an 89mm engine, so your figures of 14hp less for SUs are not too shabby, it's just the totals where it would need work.

 

Everybody has an opinion it's just that...PM me if you wish to discuss.

 

 

Thanks for all that Mick. I think I am coming to the conclusion that I have it about right on both my cars, for road use.

Cheers.

 

Mick Richards

 

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Hi Mark,

Do you have any bhp figures (@ the wheels) for your new excellent sounding engine?

Cheers,

Mr Curious.

No is the short answer.

 

The rolling road was to get the car running right with correct jets and that was done.

 

Perhaps I should go do a power run just for info, but whatever it says the torque and drive ability are top drawer and I love it with Webers...

 

Opinion is c165 crank horses.

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Webers will give you more HP at the top end of the rev range than SUs, which is why the Works' TR4 Rally cars were fitted with Webers from late 1962. But then you have to ask yourself, "do I want to be using those sort of revs on my road car?"

In my case, the answer is "No", so I am happy with SUs which perform well to 5000 (and a bit more, if necessary!).

I have driven 3VC to the NEC (and back) for a couple of Classic Car Shows, and I can say that I have been unable to detect any difference in performance on the road from my own 4VC, other than the fact that 3VC is more difficult to start and to drive until it gets properly warmed up. Curious because I run a 3.7 axle, but 3VC is on either 4.1 or 4.3, so one would expect its acceleration to be quicker.

Ian Cornish

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Interesting, but from my conversations with some of the former works drivers years ago, I got the impression that they were wringing all the revs that they could out of the 4s . . . . .

 

Graham will no doubt offer the pukka account, given that he was in charge back in the day . . . . .

 

Cheers

 

Alec

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