low compression woes

[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.

[captaindonutbikes]

I was concerned about the torque settings on the head.

doubled up the clymer manual spec after chatting to an old honda mechanic in woodford. seems to be much better going to try starting it her again tonight.

come on! 

[pae]

just had a look at the Haynes for the 650, and the M8 bolts should be 17-22lb ft (23-30 Nm) so your original numbers aren't far off that. Does feel pretty weedy when you torque a head to only those levels though, don't it?

The few M6's on the 650 are less than half these values. You hardly seem to turn them past finger tight and the torque wrench clicks.

Phil

[captaindonutbikes]

me thinks its a bent valve (s) , but will not give up. 

[captaindonutbikes]

lifted the head and found these 4 little offenders.


4 bent exhaust valves, thankfully not run or any damage to the seats.

all parts have been ordered so watch this space!

( i love the learning curve of having your cam 180 out then sorting it then finding the damage)  

[florence]

Ouch!

At least you know what it is now.

[Bryanj]

180 out dont matter as both outers come up together, more likely your mechanicaly trained spider forgot to hold the cam followers up when fitting the cam cover

[matthewmosse]

ouch, surely a good used head is looking tempting at that stage? what's the real world oppinion on installing replacement valves by the way, get the stems replaced and reamed as per factory manual or drop in a new set of valves and 'feel' for clearence or even re use some old valves that are streight? reason I ask is I have a really nice cylinder head with 8 valves bent, that would be expensive by the factory manual way but if needed I have lots of spare valves with no visable dammage to them.

[Bryanj]

If the valve guides aint cracked just replace with used valves and new stem seals, remembering the warnings when re-fitting the valve cover!!

[captaindonutbikes]

no damage to the seats or valves guides. got away likely me thinks.

parts are being sent today, progress will be friday night/saturday

[UK Pete]

Wow seems like you were lucky not to mess up anything else, good luck with the new valves
Pete