Don Terrill’s Speed-Talk

How many degrees is "bouncing around horribly"? I've run A and B series engines and don't remember any significant spark scatter. A flywheel trigger would certainly be more stable but I'd still want to investigate the cause of the erratic timing, just in case it's a symptom of some kind of...

But that would be *gasp* in contravention of the rules!

Methanol can be problematic with two-stroke engines as well - as you warm up the engine fuel collects in the crankcase, then when you leave the line one of two things happen. It will run pig rich until the extra fuel in the crankcase has been used up then clears up, or alternatively the other scenar...

Downside to surface gap sparkplugs, is they will foul faster as they run cooler. That's why they need a high energy ignition with a fast rise time - to fire them when fouled. Being fouled is almost "normal" for them. In many applications - like outboards - they are chronically wet and/or ...

Possibly totally irrelevant but.. a few years ago I had severe skirt scuffing with a big bore two stroke. The problem was exacerbated by the very large intake port which reduced the bearing area of the thrust wall greatly. I switched from a synthetic oil to a castor blend (Shell M) and the scuffing ...

So things like a heterogenous mixture or ignition weaknesses might be the sort of things you'd typically address?

So we test our engine and discover an undesirably large variation in the quality of combustion amongst the sampled cycles. What are typical causes and remedies for this and how is the cause determined?

I'm guessing the Husky used rolling element bearings in the bottom end at least - common with 4T singles - and this eases the oil requirements greatly. Stihl took this to its logical conclusion with its 4-Mix four strokes and virtually eliminated the oiling system by using two-stroke style premix to...

This question sometimes comes up in hydraulics, and one of the main considerations is aeration. A small capacity means a very short residence period in the tank, leaving very little time for the air to leave the oil. In an engine you'd have to consider whether it would survive on a diet of aerated o...

Everything that needs LUBE was coated in assembly lube during assembly. As long as the long-block doesn't sit on a pallet for weeks or months, there's no need for PRE-LUBING that's more involved than pouring some oil over the rockers before bolting the valve covers on, and pouring oil down the leng...

David Redszus wrote: ↑Mon Feb 18, 2008 10:19 pm
If in doubt, can you walk back home?

That's a good point - at least in an airplane you can be confident of making it back to the ground...

How round is round enough? I guess that's going to mainly depend on the conformability of the ring but at what point do we say "that'll do" and move on to a more productive use of time? Should we be willing to accept a tenth, five tenths, a thou? It's generally accepted that there are adva...

BTW, I think you mean't to write that flow varies with the square root of pressure. Yes, thanks Bill. Or in other words it takes four times the pressure to double the flow, so a relatively small change in the pressure drop across the jet - as you'd get from a change in the fuel level in a float bow...

I've always been a bit sceptical about the effect of small changes in fuel level having an influence on AF ratios. When you consider that it's not unusual to have a signal of 20" H2O at WOT at the booster - and a similar drop across the main jet - then it's hard to imagine a difference of say 1...

Johnno, is this one of the 9-port Holden red engines? If memory serves me well, I believe the 215 cu. in. Rover V-8s did quite well with two 1-3/4" SU's or Zenith-Strombergs? If your inline 6 is near to this displacement, an alternative might be to work up an intake that will accept 2 SU's and...