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OK, since you didn't mention a make model, year or number of cylinders this is just an old mechanics take on the situation. Blue smoke on deceleration (closing the throttle) is because of high vacuum in the cylinder pulling oil past either the piston rings or valve seals. Usually, blue smoke on a cold start is caused by the valve seals leaking into the cylinder while the bike is sitting. A quick check to see if the piston rings are at fault would be either to come down a long steep hill or accelerate hard then close the throttle, if it emits a sizable amount of blue smoke when you open the throttle again, the rings are most likly at fault. The oil getting black is it doing it's job of keeping the engine clean, and the oil consumption you mention would not necessarily be cause for concern on an air cooled engine, especially in a warm climate. Is it possible this condition existed before all this work was done? If so, I'd suspect a carburetor problem, an over rich mixture, possibly because of a faulty float valve or the float itself contaminating the oil with raw fuel, especially if the bike is left on the side stand without the petcock being turned off. To sum things up, a leak down test will show the condition of the rings and valves. Also might mention that if newer type (usually blue or green color) valve stem seals were used, there is a special procedure for installing them not all mechanics are aware of. The valve must be put in the guide first and the seal worked over the stem with the thumb then it can be tapped down onto the guide. Hope some of this helps, Frank
With the valve rocker covers off and magneto inspection plug and centre plug removed, turn motor using nut on magneto, counter-clockwise until a line appears centrally in the inspection window. This will be at Top Dead Centre (TDC).
To check this, all rockers should at rebound with all valves closed. There should be a tiny amount of play on all rockers.
If not, (being a 4 stroke) rotate motor one full turn counter-clockwise.
All engine work or strip downs must commence from the position of TDC.
Remove the crankshaft hole cap on the front cover and the timing inspection hole cap from the rear cover. remove the spark plug caps and valve covers. Put 17mm socket into the front of the motor and rotate the crankshaft counter clockwise and align the "TL" mark on the rotor with the pulsar index mark(little arrow bump).The left cylinder must be at top dead center of the compression stroke(both intake and exhaust valve rockers are loose).Now adjust the valve clearances of the left cylinder. IN: 0.08 mm (0.003 in) EX: 0.10 mm (0.004 in) Adjust so there is a slight drag on the feeler gauge. Do not set too tight, oil pressure in the rocker bearings will zero tolerance the valves. Set the valves too tight and you damage the rocker bearings. The motor is now in the correct position to adjust the cam chain tensioner. Loosen the cam chain tensioner lock bolt located right above the rear cover timing inspection hole. When the bolt is loosened the cam chain tensioner will automatically position itself to provide the correct tension. Retighten the tensioner lock bolt. Next turn the engine and align the "TR" mark on the motor so the right cylinder is at top dead center of the compression stroke and adjust the valves.
adjusting the valves simple to do pull the spark plug and the 2 inspection covers top of the head.remove the 2 inspection plugs lower left side engine cover small round one and the larger one. Use a i believe a 14 mm deep socket with a 3/8 breaker bar and rotate the crankshaft counter clockwise watch the rear rocker arm go down as it starts to come up look in the small inspection hole if you have a flashlight rotate it slowly until you see a line with the t mark before it in the small hole stop it there that is top dead center then you can set your valve settings.
Not sure what state of "togetherness" your motor is in but, there is an inspection bolt hole on the front side of the magneto cover. Take this bolt out together with the sparkplug and remove cylinder head cover. Turn engine till a timing mark appears in the centre of the inspection hole. The piston/crank will be at TDC (top dead centre) if magneto rotor is keyed on correctly. Do not set anything on engine other than at TDC. Magneto is tightened on to crankchaft end with a locating key, this covers your spark timing.
Valve timing is achieved via the cams, place camshafts into cups at TDC (all valves will be shut) and timing marks on camshaft sprockets will line up with line on cam cup journals in the head. Camchain is fed on from opposite side as chain tensioner to ensure timing remains when tensioned. Let me know if you are "all parts on the bench" or contemplating a stripdown, I can then clarify all necessary steps.
The site link below will give you the info you need from a free download.
Select your make, model and year and download a free manual...it's a big one, about 26Mb.
Then get yourself some metric feeler guages and go for it! http://www.yamahaownershandbook.com.au/index.php
First, let's assume that the valve tappet clearances are set correctly and the cam chain is properly tensioned. This will eliminate these as possible sources of excess mechanical engine noise.
If the noise is, in fact, 'piston slap' - then a teardown and inspection of the top end is called for. And yes, in addition to resolving a worn piston and cylinder bore, it would be an ideal time to examine the valve train for needed service. At a minimum, remove the valves and clean all carbon from them and the cylinder head and ports. Check for excess valve-to-guide clearances and pitted or worn valve seats. Usually, these engines are just fine with a cleaning of the parts and a re-lap of the valve seats. Replace all the gaskets and valve guide seals - and you should be ready to rock and roll.
Hi, with a cold engine, do the following.
Turn off ignition, fuel and remove seat and tank. Undo the central magneto inspection window and 17mm timing mark bolt on the LHS engine cover. Take out a sparkplug. Remove both valve rocker covers.
Turn motor counter-clockwise (using a socket on the nut at the end of the magneto spline) until the timing mark (T) lines up with the centre of the inspection bolt hole. Check all four rocker arms have a slight amount of free play, if not, rotate engine a further 360o. When all four valve rockers have some play, the piston is at top dead centre of compression stroke when all valves are closed. Your now ready to set the gaps.
Loosen lock nut with a ring spanner and adjust gap with a screwdriver, place feeler gauge under tappet between valve stem. Tighten down screw till moderate pressure is felt when sliding the feeler guage. Tighten lock nut ensuring screw does not tighten with it. Do all four valves and crank motor over a couple of revs by hand and check gaps again.
Gaps are as follows:
Inlet 0.08mm - 0.13mm
Exh. 0.17mm - 0.22mm
I need a little advice. I pulled the tank today to change the air filter and decided to investigate the valve inspection process. Well it's easy to get to the rear cylinder but next to impossible to bump the #4 position valve into TDC. The Falco writeup only talks about the bump but there's got to be another way. Right?
Second question, what's the best way to remove the air box? It sure looks like a lot of plumbing that needs to be disconnected, and I can't see any other way to get at the front valves.
Any help is greatly appreciated... BTW, getting the tank off, and back on, was a breeze.
,With the bike on the centre stand select a fairly high gear and turn the back wheel by hand until the cam is where you want it .
Plumbing on air box isn't too bad , you wil also need to move the top radiator hose to get to the lower left screw on the front cover . It has been done with a long ball end allen key , without removing the top hose .