petef
Full Member
Posts: 73
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Post by petef on Feb 22, 2019 14:15:48 GMT
Next question guys, what sort of compression pressure should I get at cranking speed on a 250N?
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Post by mikef on Feb 22, 2019 17:15:52 GMT
The manual states 185 ± 14 PSI. It is measured with the engine at working temperature with both spark plugs removed and throttle wide open.
Most bikes with a few thousand miles on the clock will be a good bit lower. Both cylinders should be quite well balanced though.
The manual states that the cylinders should be within 57 PSI of each other which is a bit strange. I would have thought they should be within 20 PSI of each other at least.
Mike.
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Al
Full Member
Posts: 148
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Post by Al on Feb 22, 2019 17:25:26 GMT
The manual states 185 ± 14 PSI. It is measured with the engine at working temperature with both spark plugs removed and throttle wide open. Most bikes with a few thousand miles on the clock will be a good bit lower. Both cylinders should be quite well balanced though. The manual states that the cylinders should be within 57 PSI of each other which is a bit strange. I would have thought they should be within 20 PSI of each other at least. Mike. That can't be right, can it? It's a heck of a difference between two cylinders and surely, it can't be possible to get both cylinders within the permitted tolerance (+/- 14psi) with 57 psi difference! Odd. Could be a misprint. Maybe that should be 57 Kpa? |
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petef
Full Member
Posts: 73
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Post by petef on Feb 22, 2019 18:40:49 GMT
Ah, I think I know where the extra horses are hiding then  I'm getting about 80. Head off time then (sigh) |
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Post by buster on Feb 23, 2019 7:32:50 GMT
Ah, I think I know where the extra horses are hiding then I'm getting about 80. Head off time then (sigh) dont worry too much till youve had a look at the bores and slugs (and dont be surprised if theyre in good nick) could just be a bit of cylinder head work gets you your compression back  |
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petef
Full Member
Posts: 73
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Post by petef on Feb 24, 2019 9:53:53 GMT
OK, head and barrel off.
Barrel and piston within tolerances.
Valves definitely need grinding in but not too bad - no serious pitting.
Exhaust valves were a bit sticky in their guides but cleaned up OK.
I'll report back.
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I'm getting about 80.
