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Just an Latest on rebuild state of affairs

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2wrench

2wrench

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Just an up-date on rebuild state of affairs

Parts all over the garage need to be cleaned,
rebagged and organized.

Car engine bay is being repainted, see photo below.
(Note by fear and trepidation, trying desperately to
paint without removing another thing. Reached max
capacity for dismantlement.) I laugh at myself now
and likely more later for this.


Engine block; head sit idle awaiting return of machine
shop guys on Jan. 2, 2008.

Preparing to ship off my rocker for rebuild.

Pondering: Upgrade cam one notch or stay completely
stock? Big question. Gas being what it is, I hear
cam upgrades keep on costing at the pump. Whadayathink?

Now the horns blow and enter...and enter...well, guess
I don't have a name for the car yet, but here it is anyway.

P1010002-5.jpg
 
Re: Just an up-date on rebuild state of affairs

Upgrade 1 notch unless the stock one is in perfect shape.
 
Re: Just an up-date on rebuild state of affairs

These cars were so de-tuned, shaving the head and a cam upgrade will go a long way to a more enjoyable ride.
 
Re: Just an up-date on rebuild state of affairs

Note that shaving the head will actually improve fuel mileage; while a slightly warmer cam won't cost any unless you use that extra horsepower on tap.
 
Re: Just an up-date on rebuild state of affairs

Okay. Thank you, gentlemen. I will go up just one
notch on the cam. Power on demand, works. I've decided,
end of that discussion.

Shaving the head?? Doesn't this take me to a place where
all bets go off on stock settings (tuning) and
stock parts (different size push rods) and anything
else that would get a novice mechanic into trouble?

Consider this: I am going with a machine shop fellow who
comes well recommended but admits has no experience
rebuilding Triumphs. So when he says to me: How much
do I shave in order to achieve 9.5:1, I say....duh...
errrr...well, I'll have to get back to you.

Kinda feel like if I don't know what I'm doing and can't get it from a book, I have little to no business, at this
point, anyway, doing it.

Same time, don't want to do something only to learn
should have done something else?

Novices, novices....but, we do love our cars...at least,
I do.
 
Re: Just an up-date on rebuild state of affairs

Surely someone knows at least a ballpark amount to take off of a stock 74 TR6 head to get 9.5:1 (with stock pistons & rods); but I don't.

However, it's not that hard to measure yourself. Start with the basic CR calculation : (swept volume + unswept volume) / (unswept volume). Swept volume is easy (if your cylinders haven't been bored oversize), it's just displacement divided by number of cylinders, so 2498/6 = 416.3 cc.

Unswept (combustion chamber volume) is a little harder but not too bad. I'm sure someone will correct me if I'm wrong, but I think stock TR6 pistons have flat tops and zero deck height (that is, at TDC, the piston tops are even with the surface of the cylinder block). So we can ignore that aspect and concentrate on what's above the deck.

The head gasket usually doesn't contribute much, so we'll assume that it's the cylinder diameter (7.47cm) and it crushes to .152cm thick (.060"). Start with one of those square pies (7.47/2)^2 * 3.14 times the thickness gives us 6.57 cc dead space for the gasket opening.

Now you need to actually do some measuring. One of those graduated syringes is probably easiest, if you can pick one up at the drug store or whatever. Flip the head upside down and drop the valves into their holes with a smear of grease for sealing. Prop the head up so it's perfectly level, then use the syringe to fill one cylinder with water until it's exactly level full; keeping track of how much it takes. (There are more accurate ways to do this, but this is easier and should work well enough.)

Now take the numbers you've got and plug them into the equation above; the answer should be pretty close to the published CR for your motor.

Now you need to know the size of the opening to the combustion chamber. Get some graph paper, the kind ruled in 1/8" (or 1/4") squares, lay it on the head and rub the edges of the combustion chamber onto the paper. Now count all the squares, taking your best guess as to how much of each partial square to include. Multiply the result by the square size in square cm; which will give you the opening size.

Now a little simple math will give you how much to remove from the head. I'd do an example, but my break is over and I'm going back out to finish tuning the Stag for the New Year's Day run.
 
Re: Just an up-date on rebuild state of affairs

2wrench,

Unless you increase the compression, leave the cam alone. Compression is what makes horsepower..period. All other mods are enhancements on that one thing.

My original advice stands:
1. Balanced engine assembly
2. 9.5 compression (see goodparts link in the previous post)
3. Goodparts GP2 cam or TSI S2 cam

The resulting engine will tune much like a stock car, but have 20-25 more horsepower.
 
Re: Just an up-date on rebuild state of affairs

And will likely be stone reliable for a long time, too. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
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