Sprint fast road engine rebuild

[iandollysprint]

I will be embarking on a sprint engine rebuild this winter to bring the motor up to more modern standards and I am looking for any advice, pitfalls, must do's etc.<br>
<br>
Engine has original 62k miles with full service history but also comes with a report of bore wear on cylinder 3. Engine pull strong as is. Head has been skimmed once in it's life.<br>
<br>
Plan is as follows<br>
<br>
Head rebuild - new guides, followers, recut valves and seats, ported inlet to match manifold, polished exhaust.<br>
Jigsawracing fast road cam (similar to STR091 I understand)<br>
New Timing gear including vernier pulley.<br>
Bored block to 20/40 thou oversize depending upon current wear. New pistons and rings. Blanced bottom end with lightened flywheel.<br>
Twin 2 inch SU's (already purchased), reamed out original manifold by jigsaw. Original cold intake set up (no pancake crappy thingies)<br>
2 inch sports exhaust (Rimmers)<br>
<br>
Thats about it. Obviously suspension and brakes to match.<br>
<br>
From what I have read this would yield around 160 bhp after being properly set up.<br>
<br>
Any advice before I delve in would be much appreciated, particularly on power output claims, camshaft choice and exhaust choice.<br>
<br>
Ta very much<br>
<br>
Ian

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[Jon Tilson]

doubt you'll find new rockers though....so hope the originals are okay.<br>
Jonners

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[Sprint36]

Just a few extra points:<br>
<br>
If the car has only done 62k then you may not need new guides. If you do get some, bronze ones may be a good idea. There used to be some bullet ones from Triumphtune which intrude less into the ports. <br>
New followers are a good idea as these can crack. <br>
Get three angle valve seats if you're having them cut anyway.<br>
At that sort of mileage the block shouldn't need boring more than 20 thou surely. check availability of pistons first. If you can't get any you could get an 1850 block bored to Sprint dimensions.<br>
Vibration Free do good balancing. Are you getting the rods and pistons done too?<br>
Rimmers sports exhaust is not 2 inch.<br>
Don't forget the oil and water pump too, and the distributor.<br>
<br>
David

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[Sprint36]

See Ben Tomkins' <!--EZCODE LINK START--><a href="http://www.bodgerben.com/tuning.htm" target="top">tuning page</a><!--EZCODE LINK END--> for some useful info. Also see if you can get your hands on a Triumphtune manual.<br>
<br>
Forgot say before - get some uprated conrod bolts like ARP.<br>
<br>
Also have a look at <!--EZCODE LINK START--><a href="http://www.sprintparts.triumphowners.com/" target="top">Sprintparts</a><!--EZCODE LINK END-->.<br>
<br>
David

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[Carsreunited]

I'd advise against getting an L1 cam (if that's what it is). An STR91 will give similiar power gains across a broader power band. The L1 only comes in at about 4500rpm, below that its not a very nice drive. I think Mark has had some cut from blanks so you can still get one from him. He might have had some TT10106's done which are nigh on identical to the STR91. Ask him which one he means.<br>
<br>
Other than that, Aldon flame thrower coil, leccy ignition (Jodsport maybe!) and a high torx starter.<br>
<br>
Have fun with the build!<br>
<br>
Edit. and magnecor leads!<br>
<br>


<p></p><i>Edited by: <A HREF=http://p206.ezboard.com/bthetriumphdolo ... eunited</A> at: 17/8/06 6:13 pm<br></i>

[iandollysprint]

Hey great info. Thanks<br>
<br>
3 angle job would be done.<br>
Availability of pistons is a bit worrying. Whats the crack here?<br>
Rimmers is not 2 inch? I asked then to measure the OD of the sports exhaust and I got 50mm as the answer. Is this NOT correct. I am paranoid about my exhaust size!!!!! 2 inch at least it must be for 160bhp.<br>
Oil pump - again this will be done<br>
<br>
Thanks<br>
Ian

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[iandollysprint]

Anyone got a spare triumph tune manual?<br>
<br>


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[iandollysprint]

So what cam should I go for?<br>
<br>
STR091? Are they available. I am after good driveability with a buzz to the top end. I have a big daft old M6 BMW which has hairy cams in it and not much happens below 4500 but things go crazy after this. Looking for somethings a bit more subtle in power delivery.<br>
<br>
Rockers - again what is the crack here. The current head is very quiet, how do I detect excessive wear on the rockers?<br>
<br>
Car has illuminition electronic ignition which I plan to keep so the flame thrower and magnecor leads seems a good idea. Where can I get these from?<br>
<br>
Thanks again<br>
<br>
Ian

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[Stephen Grellet]

Fit new performance single valve springs, clean the ports up, dont open them up, just clean up any rough casting marks, and align the ports and manifold. I have never had any problems with rockers cracking or breaking up to 8000 rpm.If marked thay can be refaced. Providing the engine has had a good oil supply they shoudnt be worn. Bore wear is also unusual in these engines if properly maintained. Make sure the front camshaft tunnel in the block isnt worn, hare again a good oil supply would make this unlikely. Remove all the oil gallery plugs and get a long stiff bristle brush and give them a thorough clean.Properly put together this should give nice power and torque, even if you stuck with re-needled 1.75" SUs.<br>
Regarding the leads I think these are expensive for what they are. Check your existing leads for continuity and if ok re use them, or if not you can rewire the existing terminals with carbon core leads. I run standard copper wire leads and these have proven to be fine, although there is no radio suppression.<br>
<br>
Good luck with the project<br>
Stephen

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[Carsreunited]

StR 91 will be perfect for your need (or the TT10106). A reprofiled cam will need Rover SD1 size ranger shims or maybe even bigger. It will be easier to shim up a cam cut from a blank. They are more expensive but I personally think they are worth it (unless you come across a ridiculously cheap and in good condition 2nd hand one).<br>
<br>
Magnecor leads are about £60 for 4 and you can order them direct from Magnecor.<br>
<br>
The Aldon coil is supplied by Aldon Auto in the west mids. They really are a good coil and back to back with a Lucas Gold coil I saw a bhp gain as well as being smoother higher up the rev range.<br>
<br>
You can open up the cast manifold slightly and purchase Sprint Parts's downpipe which is 2.5 inch bore. That is plenty. Couple that up to the Rimmers sports exhaust or get a custom side exit racer style system made.<br>
<br>


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[Leeds Sprint]

How does an uprated coil produce more bhp over the standard coil? Is it another case of getting a bigger spark? Do you need to regap the spark plugs or adjust the timing with an uprated coil.<br>
<br>
Chris

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[Jon Tilson]

I hear the experiences of these raceing boys my take on the ignition thing is that enough is enough and more than enough is pointles....<br>
You only need to light the spark plug!.<br>
Any more risks breaking down the lead insulation...and irregular misfires will result.<br>
<br>
So the std coil is fine...the weak link is the contact breaker and condensor. Replace these with a transistor switch trigger that keesp the points with minimal current and you will always get home..<br>
If you up the ignition voltage you may get better combustion of an iffy charge...but you need the leads and plugs to cope..and you wont damage yourself with shocks as you pull leads off to diagnose a fault...<br>
Ouch! I hate this modern stuff...<br>
Jonners<br>


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[Carsreunited]

I don't know the physics or engineering behind it but I saw the graphs with my own eyes and watched the car being run up on both occasions. It gained 6 bhp at peak. Might not be alot but for £40, probably the cheapest bhp increase you can buy. I've also experience of people from the V12 Jag fraternity fitting very expensive coils that throw out a bigger jolt. I have to say though, pretty much as Jonners says, there is no point putting on a stronger coil if everything else remains standard.

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[davepoth]

Not from a power point of view. But I read somewhere (Probably on Austin-Rover.co.uk) about BL doing research into "Lean Burn" technology, which utilised a High Voltage coil to produce a much stronger spark, causing more complete comubstion, which let the engine run leaner for a given power. But then I might be imagining it.

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[Jon Tilson]

What you say is true...<br>
But lean burn technology requires the metalurgy to go with it.<br>
So if you run your slant4 with a fat spark, weak mixture etc you will get hotter combustion temps and what is that going to do to the pistons and valve seats?<br>
We've seen the results in pics recently of detonation damage to pistons. There isnt a lot of scope for pushing them I reckon...especially not standard old components.<br>
If you can afford forged mahles then by all means go fo it...turbo and NOS too...<br>
But Ive also had misfires from big fat sparks with inadequate leads draping over damp cam covers...and tracking caps and failed rotor arms too.<br>
<br>
Horses for courses...<br>
<br>
Jonners

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