Warm up/idling time

[Gripper]

With the temperature dipping to 0 degrees (celcius) most nights and into the early hours of the morning, I often find myself questioning whether I'll venture out to work on my bike or opt for the warmth and comfort of the car. Most often I find myself braving the cold simply because I love getting on my bike and I hate that the season is so short up here that I want to take advantage of as much riding as possible.

My question is regarding warm up time. How long do you feel is appropriate to let the SH150i warm up before heading out? Keeping in mind the engine temp needle is pointing to COLD.

cheers,

[pagemaker]

I treat the SH like a car: idle for a couple of minutes to loosen up everything and get the oil flowing; drive it slowly for a couple of blocks so that the other lubes not involved with the engine (wheel bearing grease, etc) also warm up. I can't imagine anything else being necessary.
- Pagemaker

[robber57]

"Warming up" an engine is controversial, the logic says that the oil has to heat up before it can flow and start lubricating but the other side is that during warming up the enriched fuel mixture condenses on the cold cylinder wall ruining what little lubricating oil there was left from the previous run, the condensed petrol dilutes and destroys the oil film thus creating metal to metal contact causing wear...


My idea : modern power-plants are not warmed up at all, the are just started and start delivering electric power immediately, although latest models often have a "warm up" regulation which prevents the engine from delivering more then 50% during the first few minutes.
These engines (like in a Honda 15 HP generator)last more then 20.000 hours before rebuild is considered/necessary , average load would equal approx. 40 to 60 KM/h (25-35 Mph) making 20.000 hours equal 80.000 to 120.000 Km (50.000 to 70.000 miles)
If i could do over 80.000 km's with this engine i would be more than happy....

Thats what i do: start and drive to work, the first minutes with moderate to low engine load so essentially i drive it like a car

[bigbird]

I would let mine idle for about 1 minute on the first cold start of the day. I am of the theory that metal parts should expand slowly, because the rate of expansion is not consistent for different metals and alloys.By riding away immediately with vigorous throttle, the parts can be unduly stressed.

Many pistons are cam ground. That means their shape is not perfectly cylindrical when cold. As they warm up and expand, then their shape becomes cylindrical. The reason for this is because there is more stress on one side of the cylinder due to torque forces from the crankshaft motion. Cam ground pistons minimize the torque effect against the cylinder wall when fully heated.
Does the SH150 have cam ground pistons? I don't know, but most automotive engines do.

[robber57]

I don't think cam grinding is used anymore, cnc is the technology of nowadays, and yes i am pretty sure that a SH piston is not a cylinder shape.
In fact, i have never in my life seen a cylindrical piston, even air compressor pistons are not cylindrical.
They all are tapered ovals although often at 4 stroke pistons the oval shape is not there, in stead the manufacturer removes material on the sides of the piston, same effect and you reduce the weight as a extra benefit.

on 2 stroke pistons the material is often not removed to get additional sealing for compression since 2 strokes have ports and the "gap" from the removed material would cause leaking across the ports.
So on a 2 stroke piston you will find a oval shape.

A 4 stroke piston , the removed material on the sides is clearly visible :

btw: its a big bore kit for the SH


A 2 stroke piston:


The tapering is substantial (much more then the oval reduction in diameter), usually on alu pistons in a cast iron cylinder (bushing) it can be up to 0.1 mm or more for pistons <250 cc.
The tapering is to adjust for the expansion of the piston crown when it heats up from the combustion.

[bigbird]

The term "cam ground" is still used by GM in describing the shape of their pistons, not the process by which they are shaped. As you stated, they are oval shaped.
Back to the topic.

[Gripper]

Thanks to everyone who contributed to this discussion for your comments. And it's good to see some lively discussion on this board.

[bigbird]

Thanks to everyone who contributed to this discussion for your comments. And it's good to see some lively discussion on this board.

So, what did you decide to do?
No warmup, short warmup, long warmup, or?

[Gripper]

Thanks everyone. I decided to pretty much do what I'd been doing all along with concurs with others. I allow the bike to warm up for about 30 seconds to 1 minute and then drive away slowly (30-40 km max) for a few blocks. I have not encountered any problems with this.

[bigbird]

Thanks everyone. I decided to pretty much do what I'd been doing all along with concurs with others. I allow the bike to warm up for about 30 seconds to 1 minute and then drive away slowly (30-40 km max) for a few blocks. I have not encountered any problems with this.

That sounds more than reasonable.