96 Sport : Engine dies after starting

[WaiNYC]

I am such a neophyte.... I didn't even know there was such a thing as tappet noise Did some research and it does appear that @breakwellmz and @Puffs were right on the money (big thanks to you both).

Valve clearance was gonna be the next item on my to-do list. Am surprised that the impact could be this much. With my (current) limited knowledge of motorcycle mechanics, I'll never know for sure if and how the valves were the reason for the engine die-out. But the explanation sounds reasonable.

More questions: The most complex bike jobs I've ever done were carb cleaning and changing brake pads Instructions on the Yamaha SZR660 service manual seem to be quite straight-forward. I should be able to handle this and do it in one afternoon, shouldn't I?

And, other than the valve adjuster tool (yamaha p/n YM-08035), are there any other special tools or replacement parts that I need to get for the job?

Many thanks for hand-holding me through this.

[breakwellmz]

Glad you are getting somewhere.
Valve adjustment is easy to do and you don`t need any special tools apart from feeler gauges, go for it!

[WaiNYC]

HI... I am trying to do the valve clearance but got stumped by a lack of tools. What do you use to loosen this upper left bolt?

A regular slotted screwdriver doesn't work. I've ordered a 7/16" slotted bit, but the tip is too thick.

Any suggestions? Best if you are kind enough to show me a pic of the tool/bit. Thank you so very much

[breakwellmz]

I didn`t bother with removing that but took the spark plug out and put a rod down the plughole to find TDC.

[Puffs]

For things like that, in the past I made a tool as shown here on the right:

However, I rarely look for some TDC mark, but do as breakwellmz says: feel through the plug hole. You have to take the plug out anyway. I use a very 'special' piece of wood for that, in order not to damage the thread or so, shown on the left.

2 more tips:
- This is a four-stroke (4T); the piston makes 4 'strokes' in each cycle (1.compression stroke: going up to TDC [Top Dead Centre] with the valves closed to compress the mixture, 2.power stroke: after the mixture combusts, still with the valves closed, it pushes the piston down to generate the power [= force x travel / time], 3. EX valve opens and the piston comes back up to TDC, to push the exhaust gasses out, and 4. EX closes & IN valve opens, to aspire a fresh mixture when the piston moves down again.) You want to adjust the valves when the piston is at the first TDC, the TDC at the end of the compression stroke. That's when they should have the prescribed clearance. You can feel where you are from the resistance given by the valve springs, or rather the lack thereof. When valves are being pushed open, the springs on that give resistance. At the right TDC there is no spring resistance, around the other one there is.
- I don't know how you plan to rotate the crankshaft to that TDC. What I normally do, with the bike jacked up & the rear wheel off the ground, is put it in gear and move the crankshaft using the rear wheel. Top gear is easiest. If the bike does not have a centre stand, and if you cannot jack it up safely, you can put it in gear and just move the crankshaft by pushing the bike forward or backward. But then it gets to be a bit difficult to do at the same time. Maybe behind the big slotted screw in the centre you'll find something to rotate the crankshaft with a key.

Good luck!

[WaiNYC]

For things like that, in the past I made a tool as shown here on the right:

The attachment Tooltje.jpg is no longer available

However, I rarely look for some TDC mark, but do as breakwellmz says: feel through the plug hole. You have to take the plug out anyway. I use a very 'special' piece of wood for that, in order not to damage the thread or so, shown on the left.

Thank you SO MUCH @Puffs and @breakwellmz for the tips. I got the right tool for the bolt but can't loosen it, so I am using your methods.

I have two quick questions:

That's when they should have the prescribed clearance. You can feel where you are from the resistance given by the valve springs, or rather the lack thereof. When valves are being pushed open, the springs on that give resistance. At the right TDC there is no spring resistance, around the other one there is.

(1) I suppose the valve clearance applicable at TDC is the "Suction" spec that is listed in the Yamaha SZR660 manual?

(2) There are three valves under the tappet cover, and I suppose it is necessary to adjust clearance for them all ?

Thank you again for all the help,

Wai

[droy]

correct - suction is a bad translation for intake. Yes what you have pictured is the 3 intake valves. IF your at the correct TDC they will all move a little (as will the exhaust valves on the other side of the engine head).

[Puffs]

As droy says.

Thanks for that pic, I have never actually seen inside a 5-valve. Seems nicely accessible!

[WaiNYC]

As droy says.

Thanks for that pic, I have never actually seen inside a 5-valve. Seems nicely accessible!

@Puffs, how do you manage to check valve clearance on your MZ without taking off this cover ? I assume you own one as well...

[Puffs]

Yes, but my MZ is one without valves - a 251.

I've owned several XT's, both 2 & 4 valve models, just never a 5 valve one. (The engine in the 660 came from Yamaha's XT/SR line.)

[WaiNYC]

My learning curve re motorcycle mechanics has got a new turn.

I started a new post bec it's a difference issue and also bec I wanted a new headline to get as much attention and help as possible. Thank you for the understanding.

See here:

viewtopic.php?f=3&t=11053