engine mods??

[renault_megane_dci]

I heard optimal orientation of the ground strap has some influence and it is basically free (need to have some washer machined and period)

[beatr911]

Oh, yeah! It's called "indexing" the sparkplug.

On combustion chambers where the plug is off to the side, like what the SR185 has, the ground strap should be closest to the edge of the combustion chamber. The end of the ground strap should be pointing to about the middle of the combustion chamber. The idea is like the cut back ground strap, where the ground strap does not shield exposure of the spark to the compressed air/fuel mix.

Another theorey is to point the end of the ground strap toward the direction of the swirling intake to scoop up the fresh charge with the plug. You need to know the direction of the swirling intake charge.

It may be worth about .02hp on the SR185. But hey, it's free and all part of blueprinting the engine.

[bschloop]

I have been gone a while due to moving, getting a new job, and all related frustration, but I have made some headway on my engine rebuild. I removed the head and stripped it down. luckily the head and cylinder walls look quite good for a bike of this age. I'll have to hone the cylinder as it is glazed, and replace the rings, but I don't think it needs to be overbored, wich is good, because I can't find an os replacement piston anywhere. the head has cleaned up nicely, but I found that the intake valve is damaged and needs replacing, along with the valve seal. I will probably also replace the exhaust valve seal just in case. I'm not sure if I can do the ceramic coating at this time, as I'm not sure it would take to the old dirty parts. I might do the exhaust port though if I can get it clean enough. I have decided to use an extra thin head gasket to get a little higher compression. then I will get the cam as close to stock timing as possible erring on the side of slightly advanced. I am trying to spend the smallest amount possible on all this, so that I can afford to replace the carburettor with a fuel injection kit. it's a $400 mod, but would allow me to map the fuel metering precisely for max efficiency. Alternately I will buy an AFR meter, and every available jet for my carb, and go to town.

any comments/suggestions?

I'll try to post some pictures of the cleaned up engine, as well as my mods soon.

[renault_megane_dci]

FI sounds the best investment as far as FE is concerned.

Polishing the head and piston crown is basically free and keeps heat where you want it : expanding air to push the piston down.

For exhaust port, I wanted to do it to improve heat distribution in the engine (less in the head, more in the exhaust gas)

[bschloop]

I have finished reassembling my engine. the only "mods" ended up being polishing the piston crown and cylinder head surface, and installing a thin head gasket. the immediate effect is that it started right up in 30F temperatures. something it has never done before. I have not gotten the bike on the road yet, but it might be above 40F next week, so we might get a road test soon. I am hopefully optimistic. I will also have my compression tester this weekend, so we can see if I actually managed to increase the compression. Fuel injection is still on the table, but not a sure thing yet.

[renault_megane_dci]

Did you by any chance took some pics ?
Me likey shiney pics :-)

[renault_megane_dci]

Any news ?
Any numbers ?

You had the bike running ?

[D.O.G.]

This may be a little off topic, but the question of engine mods to boost low rpm torque comes up again and again.

This quote is in relation to Honda reworking an existing engine design from a sports/tourer (Xelvis, VT250) to do service in a cruiser (VT250C, Magna 250).

"The engine came from the basic Xelvis which is a well proven 10,000rpm motor. To achieve the right feel and sound, the crankshaft was altered, a bigger flywheel used, longer gearbox ratios and new valves and springs substituted for old, and, most importantly, a totally different carb setting utilised. The torque curve is incredibly flat for such a small engine."
Honda VF250 V

As shown above, significantly changing the torque characteristics of an engine is possible, but it sounds like a lot of work.

[renault_megane_dci]

I came to the conclusion a N/A engine basically puts out torque based on its capacity.
Namely 25Nm for a 250.

Improving on that is borderline impossible even when you're Honda.

What you can change is :
- coming closer to this target when working on an older engine
- changing the Rpm at which peak torque occurs with influence on power right away.

At the end of the day it's always a compromise on how much you are willing to spend and what you expect from it

[D.O.G.]

Originally Posted by renault_megane_dci

I came to the conclusion a N/A engine basically puts out torque based on its capacity.
Namely 25Nm for a 250.

Improving on that is borderline impossible even when you're Honda.

What you can change is :
- coming closer to this target when working on an older engine
- changing the Rpm at which peak torque occurs with influence on power right away.

At the end of the day it's always a compromise on how much you are willing to spend and what you expect from it

You're right.
Honda didn't get more torque from it, actually it was slightly less, but the peak was a bit lower in the rev range.
23.5 Nm @ 8500 rpm vs 23 Nm @ 7500 rpm.

If I could only change one thing on a small single, I'd go for a heavier flywheel, if you could find something that fits.