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Mystery - Gutless 400 four

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Northy:
Ok Folks , brought a 400 from mate , never do that with recorded mileage of 9k (mot's  to back it up ) but he couldn't  get running right . I got running better but its gutless and has other issues.
Here the symptoms  :-
On start up smokes , but clears .
Pulls fine up to about 4.5 k then misses ,no power can rev it up to 8 k but feel like it missing on one pot, hot or cold
Not go above 60 !! feel like sock up the exhaust pipe
Using oil but once warm there no smoke or horrible noises
Oil is blacken within 200 miles
Compression 25psi lower than my other 400f on no's  1/2 same on 3/4 as comparison only.


So how you going through the thought process ...and coming to a conclusion but first this is what has been done, with no effect :- 
Swapped over Coils from running bike, carb sonic cleaned  checked x2  and then swapped over with another set , electronic removed back to points, new air clean and plugs, advance retard mechanism  checked 

However you I can hear shouting it the valve steam seals !! ...that covers the startup smoke and oil usage  agreed  so lets whip the head off have looks see. Expecting  broken rings as well 

First this head been of before ! and came  off to easy and the exhaust ports are very sooty

Umm  lots oil  so much the carbon comes off easy , note  one no.3  pot  is less oil and this confirmed by the colour of the plug
head


piston tops



So next was to remove the barrel , expect a ring to fall out ...hope all in one piece and then notice the are piston 0.5  O/S.


Bore with honing marking in place



So there looks to nothing to much wrong with piston / rings and quick check on the ring show all OK  and no slop in  bores .... could have been rebored wrong ?

OK move back to valves and just whipped one out  and it clear the valve stem seal are shot  see pictures but also note the perfect face on the valve  (plus loads of oil)   





So OK stem seals can account for oil on start up, oil usage,oil in bores (?)  but it would still run Ok and given that there no oil appears to burning pass the pistons.

However I cant see that the seals would have such a dramatic  effect on the power of the engine . Ok it can suck in oil and air and weaken the mixture but never this bad or has the thing not run in yet ?         

Tomorrow I will check the bore/piston and all the valves 

So what am I missing (apart from few brain cells !!)



   







   

Nurse Julie:
Valve stem seals, as you say, plus an air leak somewhere. The engine has had a hard 9k miles if it's already needed are re bore to +.50 Is there oil vapour in the air box?.

Nurse Julie:
Just looking at the close up pictures of the barrels, the one on the right has got some huge gouges and marks on the bore which won't help much. Looks like it has had standing water damage in the past and someone has tried to clean it up, unsuccessfully.

Northy:
Think that's oil in bores or a reflection, there's no real marks other than honing marks and the brown ones at the top.  (just been outside to check) There's not even a lip you can feel at the top either, reckon they only been in there 500 miles or so. Another 400f engine I have ,had water/ seize marks so seen them before.
 
Very little oily vapour in air box , breather pipe  and cover on the rocker box very clean. its not blowing oil its sucking it in.

Story behind the bike is it was in shop window , however I reckon its was raided for spares. So it could have seized whilst sitting there  or this might not be the right engine so I'll take the 9  k with pinch of salt. The cam is good and bearing in the head are Ok  ie relate to 9 k  not  109  :-) 
 

Nurse Julie:
So these marks are oil ? Look like holes and gouges to me but good if it is only oil.

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