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Old 29th January 2013, 16:06   #31
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Default Re: Yamaha RD350 Restoration

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Originally Posted by Kaumad View Post
One of the primary and basic goals of a newly re-built 2-stroke engine is achieving ring seal. This means a good seal between the cylinder liner and the rings. Two very important ways of achieving this is:
(1) progressive loading the engine - this means sampling the complete rev-band or at least 80% of the rev-band progressively in short bursts. Progressively means opening the throttle a little bit more to go further through the rev-band with every subsequent short run and
(2) heating and cooling cycle - this means you run the bike for short distances, switch it off and allow it to cool down. Repeat the process 3-4 times. The cycle of heating and cooling is very important to achieve a good seal. The revs should be varied and not held steady for extended periods.
The above 2 points mean you need to ride the bike proper and not baby it at idle speeds for prolonged periods of time.
Well I was aware of the heating and cooling cycle but have not made the progressive loading the engine. Even when the bike was being run in Idle (definitely not for 4 hours) throttle was being worked on slightly to alter the rev range. Have heard of this ring seal and its pluses but not in great deal.

Many thanks for elaborating it in detail though.
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Old 29th January 2013, 16:27   #32
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Default Re: Yamaha RD350 Restoration

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Originally Posted by ku69rd View Post
Well I was aware of the heating and cooling cycle but have not made the progressive loading the engine. Even when the bike was being run in Idle (definitely not for 4 hours) throttle was being worked on slightly to alter the rev range. Have heard of this ring seal and its pluses but not in great deal.

Many thanks for elaborating it in detail though.
Its not just the seal that is affected. The temperatures that build up (esp in air cooled engines - in spite of the fan) also cook the rings. The metal loses its elasticity (in fact become "soft") and there on the rings would never be able to sustain equal circumferential pressure against the wall of the bore. Causing a lot of blowby once you start loading the engine.

Last edited by ebonho : 29th January 2013 at 16:46.
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Old 29th January 2013, 22:03   #33
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Default Re: Yamaha RD350 Restoration

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Originally Posted by Kaumad View Post
Did I read this right?
You mean, you put the bike on the centre-stand, kick-started the engine and let it idle for 4 hours?
If this is what you actually did - I am sorry mate, you have overcooked the engine. The engine is toast and I would be very surprised if it even runs properly. Sorry but what you did is the absolute worst you can ever do to a 2-stroke engine.
I may not have experssed the exact process I use for running in an engine clearly enough. NO I did NOT put the bike on the center stand and run it for 4 hours straight. I use a very different method to achieve a good ring seal and have done so on numerous engines I have rebuilt both for road use and for racing.
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Old 22nd August 2013, 10:33   #34
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Default Re: Yamaha RD350 Restoration

Nice to see another restored RD, Collector small thing about cylinder and heads, you powder coated them? If yes please remove them, they wont allow the heat to go out and suffocate the engine.
After enjoying 2.5 years of my RDD ported blue RD i restored one stock white US spec RD last week, will post the pics soon.
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Old 24th August 2013, 19:37   #35
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Default Re: Yamaha RD350 Restoration

The barrels are NOT powder coated. They are painted with zinc oxide primer and heat resistant paint just as was done in the factory to the original barrels.
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