RUNNING IN 2 STROKE

[Bobber-job]

just rebored and fitted new bearings to my '74 Suzuki TS400 and was thinking about running in- the manual says (from new) 500 miles below 3000 rpm then another 500 below 3500 rpm. Im using Silkolene comp 2 with a standard oil pump. any thoughts?

[Simon Ratcliff]

It depends on the surface finish after honing and quality of the rings. Manufacturers of 'Flexhone', for example, state the rings will be sufficiently mated to the bore a few seconds after starting the engine when honing cylinders using their tool, this assumes the bore is round to within 0.0002". Earlier this year I used a 'Flexhone' when fitting new rings and ran the bike (Norton Commando) up to 80mph (approx. 5,000rpm) first time out and shortly after that was using max revs. 3,400 miles later the bikes oil consumption is averaging 2,000 miles/pint, which I'm happy with. I regularly rev the engine to 6,000 rpm and all is well to date. Running-in mileages of 1,000 miles should be a thing of the past - then again it depends on the honing tool used and quality of the rebore by the machine shop doing the work. That new vehicles need no running-in (as far as I'm aware) proves the point, I think.

[Bobber-job]

that's a very good answer! - thank you

[mervin]

dont run it in on expensive fully synth oil , it will not bed in properly i am told , use only semi synth

[DerryUK]

Some more thoughts.

When things heat-up they distort, this is why pistons are oval when cold.

Two stroke cylinders, because of their design, distort more than four strokes.

You need to put some miles on your bike to run it in, how many miles is up to you I would have thought. Every time you ride your bike ideally increase the amount of throttle to get the temperature up.

I agree with the comments about the oil.

Now having said all that if you think of the number of bikes that have been run in from new AND thinking how different people treat their bikes there seems to be very few problems attributed to running in so the routine seems to be flexible.

As an aside I bought a new car last January and the manual said no more than 4000 rpm or 100 mph for the first 1000. This is on fully synthetic oil. This may of course be down to modern machining techniques. The car is German so the 100 mph bit is them taking the mickey (IoM excluded.)

Enjoy your bike.

[mervin]

3 new seats with VW engines i have had and no mention of running in from the dealer, instruction book advises no towing for a 1000 mile but thats abut it
some say take a 2 stroke out and give it several short hard rides , just to heat cycle it, some say stick below 400 for 500 miles then below 6000 for 500 miles , but give it an occasional flat out blast on the flat or downhill

[nickjaxe]

Can I ask who you got to re-bore it for you...just about to get my Bantam re-bored.

[Antoni]

Some more thoughts.

When things heat-up they distort, this is why pistons are oval when cold.

Two stroke cylinders, because of their design, distort more than four strokes.

You need to put some miles on your bike to run it in, how many miles is up to you I would have thought. Every time you ride your bike ideally increase the amount of throttle to get the temperature up.
...

Enjoy your bike.

Rotax have been making 2-stroke engines for 25 years or so, there are variants of these intended for small aircraft. These engines have to be able to run at full power (for take-off) the first time they are used.

The installation manual for the air cooled Rotax 503 specifies a precise continuous run-in session of an hour or so prescribing 5 minute runs of gradually increased power separated by high or full power bursts of tens of seconds. Now I'm going to try to add the screen shot - it might not work!

Nope, doesn't. So here's the URL,

http://docusearch.flyrotax.com/files/pdf/d00287.pdf" onclick="window.open(this.href);return false;

It's on page 21-1.

[Simon Ratcliff]

.....When things heat-up they distort, this is why pistons are oval when cold.

Two stroke cylinders, because of their design, distort more than four strokes.

You need to put some miles on your bike to run it in, how many miles is up to you I would have thought.....

Hi Derry,

there's a few small, but significant, technical inaccuracies in the above. When metal is heated it expands. It may expand at different rates, which can be due to heat concentration, which is why pistons are typically tapered from top to bottom. The piston crown is closer to the combustion flame than the skirt, hence it has a smaller diameter than the skirt when cold. As it heats up the crown expands at a greater rate than the skirt due to the temperature gradient. The ovality is because of the greater mass of material around the piston (gudgeon) pin and this material will expand at a greater rate than the rear and front faces of the piston due to differences in material mass.

It's a generalisation to state two stroke cylinders distort (expand) more than four strokes. My Commando barrels are far from symmetrical and will not expand uniformly due to difference in mass of material, especially in comparison to a Suzuki water cooled GT750 (kettle) for example.

As I stated previously, the amount of miles required to mate the piston rings to the bore is dependent on the surface finish of the bore and quality of the rings.

Enjoy your bike....anybody going to Beezumph this weekend? I'll be on a blue Interstate.