SOHC.co.uk Forums > CB500/550

low compression woes

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captaindonutbikes:
Just turned her over with fuel in with little or no compression in 1 and 4 a small amount in 2 and 3. (not been measured yet!)

checked the timing, bang on.

checked the torque on the head, all to book spec but seems pretty loose as cylinder heads go ? 20.nm to 22.nm by the cylmer manual (is this wrong) ?

investigating top end first before checking for valve problems. ( have checked he valves clearances and they are set to book)

(damn, sh*t and bugger, thought this afternoon maybe her maiden voyage, electrics all sorted but not firing and no fuel on the plugs)

SteveD CB500K0:
What do you mean by "little or no"?

Do you have a compression tester? If so, what are the readings?

florence:
I aggree with Steve, you need to measure to know for sure.  In the absence of a tester, put your thumb over the plug hole as you or an assistant (easier) turns the engine over.  It will at least give you an idea about what is going on.

Bryanj:
turning over via the kicker gives the impression that compression is low

Yoshi823:
You might do to buy one of these... http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_199553_langId_-1_categoryId_165557

but you'd also need the Gunson adapter to fit the engine... http://www.gunson.co.uk/item.aspx?cat=673&item=1815

Once you have a reading tip a spoonful of oil down the spark plug hole then do the compression test again...if the readings go up quite a bit then the rings/pistons need doing. If the compression dosn't increase it's valve seats...have the head off & lap the valves in...don't grind them in.

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