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Oh no ... not another Engine Rebuild thread


Greeks

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Yep ... BOB needs heart and lung transplants :-(

First thing to do is get my spare engine down from QLD and get it rebuilt.

Plan so far is for Mazda pistons, 2.7l, new cam (yet to be decided).

I'm getting it done by the local Triumph specialist who's built many 2.7l engines and I'm pretty sure I trust. Converted to unleaded in the process of course.

I'm venturing into the unknown here, so I'd appreciate any recommendations for the rebuild. Would have loved to go for pi, tubular manifolds, etc, but the budget is stretched already. My main requirement is that the engine has healthy mid-range grunt for overtaking. I'm not bothered crazy about action over 5,500 rpm.

Any good do's and dont's?

Also ... anyone know the general dimensions of the full engine to help me get a quote for freight?

Cheers

Graham



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Any advantages to a 2.0 flywheel on a 2.5 ... or were all the flywheels the same through the range.

I know I've seen comments on decking before ... what spec's should I be aiming for?

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If going 2.7 ie 77mm or 77.5mm you must use a flat top block... you can create one of these with any block by taking about 0.035" off the top. With a 2.5 run the pistons 0.030" below the deck or you will get piston to head contact if you rev it hard.

A Mk1 PI crank is the best starting point... if you use Mk2 (most likely) take about 8 lbs off the Mk2 flywheel. Balance everything.

If running low compression mazda dished (8cc) pistons skim a PI head (3.400")  to 3.300" to get around 9.7:1 compression or a 2500TC head by 0.175" ... (do the maths) This will help the head breath much more than anything else. Run standard size valves with a high spec for unleaded (pm me)

Run a wade 444C Cam or genuine TR5 grind. A TR6 cast manifold would really help.. find some muppet who has fitted a crappy set of headers and doesn't want his old manifold  ;)

Try to use vandervell bearings they are far superior

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lagerzok wrote:
A TR6 cast manifold would really help.. find some muppet who has fitted a crappy set of headers and doesn't want his old manifold  ;)


Sorry if I'm a bit behind the pace here, but I take it from that comment that the standard TR6 manifold better than some alternatives? Is this just on a 2.7 engine or all Triumph six pots? Please elaborate!

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The TR6 manifold does a better job than almost anything except a proper implementation of the 6-3-1 manifold design. TBH not sure where it ranks in terms of the compromised 6-3-1 designs, e.g. the Mike Randall stuff and the Phoenix thing (although Andy should be able to comment as I believe he runs a Mike Randall 6-3-1).

The TR6 manifold is an improvement on the standard Saloon manifold and is a better option than the 6-2-1 aftermarket tubular manifolds (which personal experience has taught me are pretty awful things).

TR6 manifold works well on all six pots not just the 2.7 litre ones.

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Bill,

I'm not sure I'd class my Mike Randall 6-3-1 as 'compromised', I'd refer to it as  more of an 'early' Gareth Thomas design.

I'd be interested in comparing my 6-3-1 with the one in Steve Attenborough's GT6.

The phoenix ones with the 'orrible 90 degree bends on 1 & 6 do look rather suspect.

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Richard_B wrote:
I'm not sure I'd class my Mike Randall 6-3-1 as 'compromised', I'd refer to it as  more of an 'early' Gareth Thomas design.


All I meant was it's not quite an optimised implementation -- e.g. a Mike the Pipe 6-3-1 for Saloons I saw recently had short, unequal length primaries and used rather narrow pipework.

I'm certainly not saying they don't work -- I've never owned one personally. In any case they are definitely far superior to the Phoenix ones which are just really, really horrible things. It's not just the bends on them -- those collectors they use on the primaries are just awful  :'(

Probably fair to say the Mike the Pipe and the TT ones produced in the late 80s have been the best available to date.

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Well, it turns out my spare engine up in QLD is a 2.0 - the engine was marked as such but it had a 2.5 diff, and had been rebadged, so I was sus. as to the actual stroke - had someone actually bothered? No they hadn't.

So now I'm probably going to look around for a spare engine in Hobart and get that rebuilt... I've got options on a longtail crank, have to decide on cams, whether to go 2.7, etc.

A bit of a costing exercise is coming up this weekend I think :-)

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Well, didn't take long to track down an engine ... and possibly a good one, too. May be able to avoid a rushed rebuild, fit a recon. g/box and new clutch and spend a bit of time on turning the original one into a "Torque monster" (A Thompson, 2008 ) for a later BOB re-birth ;-D

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Turns out that the possible engine is a Mk1 Pi ... I could join the hordes of M1 Pi SU drivers now ;-D ... bit like you eh, Tim ;-)

CR1143 ... now to see whether it is exactly what it says on the tin...

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Rust_Spot wrote:
Graham - where would I get more info on the Mazda piston mod?  Sounds fun!   ;D

Cheers,
Glenn


Glenn, my source of info. has been Andy Thompson tbh. It sounds like the hardest thing to do is track the pistons down. My engine builder guy has used them before and reckons the ones he uses are the same price as Triumph ones.

I've just checked out the engine i'm probably buying and it's a Mk1 head 516816, too so that's good. And i've measured this at 3.300" so it's probably already skimmed

It has a visibly machined flywheel, but I wouldn't know how to tell if it's the lighter one.

Also a good condition distributor but I can't trace the number stamped on it. It's a 25D6 with vernier and 41529A ... anybody know what this comes from? My best guess is a 1973 TC after a bit of deduction.

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Thanks Graham.  It would be great to hear more from Andy on bottom ends.

Which cars are the Mazda 77 and 77.5 mm pistons from?  Are there any oversized pistons from other car makes that people have used?

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Mazda 323 pistons mid 80's by all account. The 1.5 twin carb high compression model has 77mm flat top pistons with the same deck height as a 2.5 but the small end bush needs resizing... I honestly forget whether its bigger or smaller but obviously it's metric.

They are a good tough piston but very hard to come by cheaply anymore. Who rebuilds a 80's Jap engine  ::) That plus the cost of the rod conversion might say the recently designed GTEVO forged ones would be the way to go if building a 2.7 nowadays.

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Ho hum ... it turns out that there isn't a long-tailed crank and lighter flywheel on the engine (although i've got a price for these), it's already 40thou oversized. No unleaded conversion has been done.

I'll find out what (original) cam is in there, the state of the bores, etc. tomorrow, but the oil was in a rare state, so it might as well come to pieces for be cleaned out and checked out.

Having been quoted astronomical figures for the Mazda pistons I'm going to leave the 2.7 for now, I need to get the bloody thing together and in the car.

So unleaded conversion is on the cards, longtail crank and lighter flywheel, cam regrind (if it's not a good condition Pi one already),

Should I still skim the head and deck the block, though?

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If sticking with early PI cam, stick with the PI CR of 9.5 or you will get bad pinking... if going longer duration you may raise it IF you have good pistons... If sticking with Triumph ones stick with 9.5 or 3.400" head height. If the head has been heavily skimmed either find another or deshroud the inlet valve to open out the chamber a bit to get the CR lower and also flowing a bit better

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CR ratio is a mathematical ratio that can be calculated but in reality is theoretical and will not be achieved .... we should talk about effective CR's... you increase the calculated CR with a longer duration cam as the effective period you have to compress the intake charge decreases with increasing valve overlap  :P  

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Yes ... Triumph world is a small world - strangely enough the owner of that car is who I've sourced the engine I'm rebuilding from (His name is Glen, oddly enough). And the guy who's rebuilding it for me is also rebuilding a Stag engine for Glen. It's enough to make your brain ache ;-D

Latest news is that there's a decent size score on the crank that's in there, so it may be cheapest to buy another ... at least that way I get the better crank and lighter flywheel ;-)

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*Cue Twilight Zone music*  Spooky stuff indeed!

Thanks for the link.  I've seen this car before (on tinternet) and greatly admired it.  Very tasty mods.

Mmm.  One day....  Better get saving my pennies!

Does anyone know just roughly what increase in power or torque going to 2.7 has?  I expect most people would change other stuff, cam, head at the same time so might be hard to say.

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