Hot Running

[Butch (cb)]

Sorting out the cosmetics last Spring I ended up stuck with a set of Armours exhaust down tubes that didn't fit. Yes I know; we've all been there, but no matter. With everything else looking resplendent in its new finish and wanting to get back on the road, what to do with the somewhat cosmetically challenged original pipes? Well given that the Bitza is somewhat Bobber style anyway I elected to buy some white heat wrap from ebay and wrap them up.

And I actually quite like the look. Sadly the engine seized shortly after and that was it for the year (details on another thread somewhere). But here's the question ... I'm running an iron head  - will I be more likely to suffer overheating issues come the Summer? I don't want to trash another engine.

[bsa-bill]

Well that's why they produce Alloy heads I reckon

Now just to add another note of caution - is the heat wrap not designed to keep heat in and you really want to let it out

[muskrat]

G'day Cyclobutch,
                        wrapping the exhaust in theory should run the motor a little cooler. The wrap is to keep heat in the pipe and due to thermal expansion increase the velocity of the gas, which in turn (due to valve overlap) drags a little more fresh gas into the cylinders. Increasing volumetric efficiency.
Iron heads do run a little hotter and a slightly richer mixture can help.
Cheers
Now I'll duck for cover !

[bsa-bill]

Thanks Muskrat - I live and learn

[beezalex]

Yes, they run hotter, particularly when pushed.  The good news is that a hot head isn't gonna make a properly built motor seize.  You'll likely just get more pinging the occasional broken spark plug and maybe the exhaust valve clarances opening up resulting in kewl flames shooting out your pipes (ask me how I know).  The way to avoid all of this is to keep the compression ratio at sane levels (7.5:1 tops) and making sure your timing is set right.  IMHO, running too rich of a mixture doesn't help much but will build up carbon, making the detonation worse and putting carbon pits in your exhaust valve seats.

On the upside, I seriously doubt the header wrap does anything but make your pipes rust and crack, at least that's been my experience.

[Brian]

I wouldnt worry about over heating. None of my bikes have alloy heads, they are all cast and I go riding on days that are in the 40's C and have never had a problem. Some days when I get home the oil is so hot I reckon I could deep fry chips in it, probably wouldnt taste very nice though 

Mine are all on 7.25-1, timing at 5/16" BTDC (about 32 degrees). I put my engines together with  a minimum piston/bore clearance of .004". The pipes blue for about six to eight inches from the head but that just shows the bikes are ridden.

Oneday I will get rich and get one of those heads made from recycled saucepans, oneday......

[nigeldtr]

Simply lover it "recycled saucepans" - never heard that one before, gave me a good laugh - thanks, needed on a cold winter evening. In Germany it also gets up to about 40C in summer, and my plunger used to nip up when under load so I honed the bores to give a bit more space and no more problems - a bit smoky when I stop at lights though - not from the exhaust, but the block and head, can't stop a little leak round the base of the rocker box.

Nigel

[Butch (cb)]

Following a recent seizure - crank main bush rather than bores, I had to have a light hone run through the bores as the rods were twisted and had marked up my new bores (250 miles on them at that point). So I should be running a little loose there now anyway. She smells hot after a run - even at this time of year. Could be because it's cleaned and kept lightly oiled over pretty much everything, or maybe I'm not used to the way iron motors and dry sumps smell ... ?