Piston or gasket kits?

[snydes]

Hi, my 1989 FZR400 I just picked up doesnt run and its because theres no compression in cylinder 1&2 and then around 80psi in 3&4. I asked the mechanic what to do and he said either change the shims or you have to get either a piston kit or gasket kit i think. Does anyone know where I can get some?

Also what should the compression be in all the cylinders?

[reelrazor]

You need a better "mechanic".

He should be able to tell you WHY the compression is so poor. 80psi is horribly low. NO compression means......damn....nothing good that's for sure. Should be 130+ psi.

That's a fairly odd cylinder mix of NO compression and poor compression. This engine needs a cylinder leakdown test to find out what's really going on in there.

Did this bike ever run in your presence?

[Evilchicken0]

It's more than likely the valves tolerances. It's not so easy to check them with the engine in the frame, although it's doable I'd drop the engine.
Once it's out check read the manual and read it again.
seal the inlet subs and exhaust openings then was the engine off - this is because you're taking off the cam cover and taking the plugs out, so you want it all as clean as possible. Get a clean sheet of paper and fold it in half on the short edge and in quarters on the long edge - so you have 8 squares . Open it up and you've got four pistons of inlet and outlet (like your cams) mark IN and OUT with 1 2 3 4 so you know where you are (trust me I've got that wrong when I did it)
Take the generator cover off.
Now move the engine crank so the cam lobe for No1 (closest to the generator) are pointing up. Use a feeler gauge between the underside of the cam and the top of the valve bucket and measure the distance. Mark it on your paper
Chances are you'll find a couple with zero tolerance, if / when you do call your mechanic and get them to reset them - it's a complicated thing to do and not something you want to get wrong.

[snydes]

You need a better "mechanic".

He should be able to tell you WHY the compression is so poor. 80psi is horribly low. NO compression means......damn....nothing good that's for sure. Should be 130+ psi.

That's a fairly odd cylinder mix of NO compression and poor compression. This engine needs a cylinder leakdown test to find out what's really going on in there.

Did this bike ever run in your presence?

Yes the bike ran before at the end of last season.

[reelrazor]

-from PM

Hi there,

what does a cylinder compression leakdown test involve? or how do you perform one?

Also the mechanic did nothing else to the bike but a compression test thats why i only know this much.

if email is better for you

A leakdown tester will apply air pressure (from compessor) to the cylinder via the spark plug hole. The cylinder being checked must be at TDC. The engine is held here, while the leakdown test ensues. There are two gauges on the leakdown tester..one is inlet pressure (pressure being applied to the cylinder) and teh second gauge reads what the cylinder is actually holding.

The beauty of this is that the leaking pressure can be heard coming from it's leak point.If the intake valves are tight, air will escape from the carb(tailpipe if exhaust valves). And if loss is through the rings or a holed piston-the air will be heard at the oil fill plug.

It is a MUCH better diagnostic tool than a standard compression test.

[Evilchicken0]

It is a MUCH better diagnostic tool than a standard compression test.

Yes, but it's kind of academic. If the rings have gone the engine is beyond economic repair, find another engine. In which case you need the engine out.
If the valves have closed up then you need the engine out (well it's a lot easier anyway) and check the tolerances.

[DonTZ125]

If the rings have gone the engine is beyond economic repair, find another engine

Beyond economic repair - for a re-ring?! That's quite aside from the 'disposable engine' midset that a LOT of FZR riders are getting into. I understand that 400 cranks are getting scarce; I wonder how many perfectly serviceable cranks and rods are in dumpsites or have been melted down for scrap ...

[reelrazor]

It is a MUCH better diagnostic tool than a standard compression test.

Yes, but it's kind of academic. If the rings have gone the engine is beyond economic repair, find another engine. In which case you need the engine out.
If the valves have closed up then you need the engine out (well it's a lot easier anyway) and check the tolerances.

Except that I can do the leakdown test in under an hour from fairings on and TELL YOU what valves are tight/burnt AND if the rings lose enough to make that an economically un-viable prospect.

It sucks to put time and effort into valve re-shimming only to find that the compression loss moves farther down.

[willandrip]

If the rings have gone the engine is beyond economic repair, find another engine

Beyond economic repair - for a re-ring?! That's quite aside from the 'disposable engine' midset that a LOT of FZR riders are getting into. I understand that 400 cranks are getting scarce; I wonder how many perfectly serviceable cranks and rods are in dumpsites or have been melted down for scrap ...

What ?
A set of rings is £200 .... if you wait 12 months for the size you need to surface after searching the net daily.
A gasket set is in the region of £200 ... and that is only using SOME genuine Yamaha gaskets.
Labour of course..... yes they give it away free at any garage/fitting shop for those that don't have the tools/skills/facilities to rebuild an engine themselves.

A complete running machine...yes the whole bike... can be easily sourced for £400.
An engine.........£150.

And all this for a bike that is worth £600/£1200 resale tops with major upgrades to brakes/suspension and fixings with good fairings and paint .

I do not consider a re-ring economically viable either.
It is not a mindset ....purely common sense.....which appears to be becoming a rare commodity .

[reelrazor]

It's about $300 USD to re ring and replace head and base gaskets with OEM.

There is some value in keeping a great bike alive.

I kind of agree with Don in that if no one tries to keep these around, there won't BE any around much longer. And, as they age more...you will see that price rise quite a bit ...IF you DO keep it around. ESPECIALLY if frame and engine #'s match.

about 15 years back I sold an RZ (RD350LC) cause it "wasn't worth repairing"...and NOW...damn. Wish I had. They are going for double original purchase price and rising.

But back to the original topic....

at least the leakdown test will tell you..hey you have leaky valves.....AND your rings are getting shitty....or rings hold well...

and now you have an accurate assessment of the engine's true state and can make a better informed decision on whether to spend on repair or replace.

[Evilchicken0]

obviously things are different in umericaland but having done the bleeding heart I must keep it alive routine you'll probably find that it's the valves afterall.

Anyway, doing the rings is more than 300 dorrah. Here a ring set is £40 to £50 head and base gasket, shims (because you'll do them anyway) then hone the bores and skim the barrels and head. You'll be regrinding the valves and when you build it back up you'll chuck a set of pugs at it with new oil ..... and as Will says there's labour on top because the kid has a mechanic.

Over here our bikes are different we don't have matching numbers because all the 400 engines are stamped 1WG. Bikes get old and wear out, just saying if I'd kept it is like saying I remember when all this was just fields ....