compression stuffed

lol you've already just delved further into the FZR than I've ever been.

I think you can get some type of acid to clean off the carbon, etc, from around the cylinder / valves, but don't quote me.


Maybe it's time to start making friends with your local Yamaha dealer. Take the head and the pistons in there and talk to them about solutions for the carbon deposits, possible causes, etc. Being actual mechanics they're more likely to be able to help, and if they know you're probably going to order parts, etc, off them (in otherwords, let them know <!-- s --><img src="{SMILIES_PATH}/icon_smile.gif" alt="" title="Smile" /><!-- s --> ) then they'll usually be quite helpfull.

 

The next step is up to you, but you have essentially 2 choices.

1. The cheap way. Hone the bore, re-ring & new big ends. Replace only what is required. You can acid clean the internals, but not really a big deal as long as they are clean of dirt, and the heavy carbon is off. Check the head & block for warping & check valves for sealing. Say $400 or so worth depending on how buggered it is.

2. The proper way. Drop the head off for full rebuild, get a bit of porting while its there. bore the block 40 thou over, new dome top slugs and full bearings inc. crank. Consider an offset grind on the crank as you will probably have to linish it anyway. Balance EVERYTHING. Consider attacking the box as well, with new clutch. New timing chain, check oil pump, water pump etc. Expect up to say $1500 total, but a very strong motor that will outlast the rest of the bike, providing servicing is maintained & good oil is used.

 

Southern cross motorsports seem good for kits.

 

(03) 9458 3239 Victoria (I think?)

 

Give 'em a go, they seem to have everything I ask for, even some obscure stuff. Although I havent had a need for them for a while now...

 

I seem to recall some-one else wanting to get the valves reground but no-one had equipment to do ones that small, but you could hand lap the valve and seats with valve grinding paste. That may fix your compression problems if the rings are ok

Honing the bore will remove any glazing on the bore and roughen up the bore to allow the rings to seat in properly, it will not alter the bore size.

The cylinders will not need reboring unless there is a noticable wear line at the point where the rings stop in the upmost part of the cylinders or the bore is out of round.

If you remove the rings check that you put them back in the same way they came out, sometimes rings have a little lip or groove on one edge or the inside edge is not 90deg to the flat edges. ie they have a top and bottom edge.

Hope that helps

 

How exactly did you get 220PSI? for two cylinders? The Spec compression pressure is only 142PSI. You must have put a **** load of oil in there.

This link to daves site will give you all the tolerances you will need. If parts are out or almost out they should be replaced or machined whatever the case may be. The FZR400 manual will tell you how to measure them.

I wouldn’t worry too much about the carbon deposits. Every engine gets them with time. Just remove loose bits and larger deposits, if you’ve got the money an acid bath is always a plus.

The mark on your piston doesn’t look like a wear mark but an oil mark where it has made its way past the rings and been toasted.

This place will do shims for around the $6~7 mark, $12 is way too high.
http://www.precisionshims.com.au/

Did you do your compression test with the cams removed from the head? Or had you already replaced the shims?

 

Definitely recommend Precision Shims. I ordered them on a Tuesday morning and received them on a Wednesday afternoon! Had the full process done in time to get to Friday night coffee and it was my first time adjusting clearances.

 

only thing I don't like about precision shims is that they don't label the new shims with their sizes. means you need to measure them with a micrometer (or keep a record somewhere of the sizes you put in)

 

you'd be surprised how much the valve clearances can affect compression. I thought you'd already done clearances, which is why I didn't say anything earlier.

Think about it - reduced clearances means the cams are pressing down on the valves sooner, and releasing them later, than they should be.
In other words, your valves are opening sooner and closing later than is within spec... So as the piston begins its compression stroke the in-take valve is still open, and the piston will push some of the fresh mixture back out into the intake manifold. That obviously means less mixture to compress, which means lower compression ratios.

Out of spec valves kill power even further, though; as the piston finishes its power stroke, the exhaust valve will open too early, letting the expanding mixture escape out the exhaust instead of driving the piston down.

On a small bike with valve timing set up for high rpms (such as the fizzer), it can become a real issue at the low RPM range - even with valve clearances within spec.
That's why Yamaha fitted the EXUP valve: to increase the back pressure in the exhaust at low rpm. That way when the valve opens early the ehaust gasses can't escape as easily, and more power is delivered to the piston.

At higher RPM the piston is moving so quickly that there is minimal difference between the valve opening and the piston reaching the end of its power stroke, so it's not an issue.

 

There are 2 types that you may be speaking of....

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or

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Dont hone the cylinder if the same rings are to be used. Anyway what are you doing reusing the same rings? If a compression test showed considerable increase in compression after putting oil in the cylinders, the rings are gone, and you will be wasting your time and money putting it back together.

Big ends can be reused, IF both surfaces look impeccably clean and smooth, and the coating has not been worn off the bearing. Once again, for a small amount, best replace what is worn.

I have been through the experience of doing up motors on the cheap trying to save anywhere possible, more often than not it doesnt work, and it costs you more in the long run. For example- I now subscribe to the old rule that you cannot do up the top of a motor without doing the bottom on an old motor, as the bottom end will not cope with the extra pressures created by a strong top.

Get a loan, save some more, whatever you have to do, but at least re-ring the thing properly