Compression testing-valves or piston rings???

[rob_scott92]

Hey guys,

my uncle got me a compression tester for christmas (proper gift )

I'm going to give it a go today but i'm not really sure on how to tell if its the valves or the rings that are worn.
I did hear a while back that if you put some oil in the cylinder, and the compression increased, that would mean that its the rings that are at fault.

Can anyone confirm/expand on that at all?

Cheers
____________________
First bike: 1982 Suzuki Gs 125 'The beast MK1' > 1988 Honda Cb 350's' FOR SPORT! (Good ol' oil burner!) > 2001 Suzuki Sv 650 's' Made it out of the 80's! > 1997 Honda Cbr 600f :p

[P.addy]

What I was told is pop a little 2 stroke down the bore, if compression increases then its the rings.
What happened to my mates GX125 was a slag... lack of compression so we popped some 2t down there... compression was the same!
Ended up being a cracked valve seat.

[Barry_M2]

You need a leakdown tester to pin point where a problem is really. This blows air into the cylinder from a compressor rather than using the piston to supply the pressure.

Yes, dropping in a little oil will show a higher reading. You could check what the actual PSI should be from the Maunal, then compare the before and after figures!

I use a leakdown tester, superb piece of equipment!
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ZXR750R (M2) - For the road.
CBR1000 RR4 - For the track.
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[rob_scott92]

Aye i've got the manual so i've got a figure to work towards.
I assume normal engine oil will do? Obviously it being 4t i dont have any 2 smoke oil lying around

will just a little oil be enough?
i'll have to find a funnel or something so i dont get oil on the spark threads
____________________
First bike: 1982 Suzuki Gs 125 'The beast MK1' > 1988 Honda Cb 350's' FOR SPORT! (Good ol' oil burner!) > 2001 Suzuki Sv 650 's' Made it out of the 80's! > 1997 Honda Cbr 600f :p

[N cee thirty]

ya the oil gets put in so it creates a better seal instead of the rings hense increasing the compression (rememeber to have the throttle fully open)

when me and chris (mostly chris) redid the valves on the cg,you could tell the exhaust valve was leaking as on compression you could hear it
____________________
'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[rob_scott92]

Actually, whilst on the subject;

Parts for this bike are either impossible to find, or are just too dam expensive!

If, say, it were the piston that was knackered, or the valves. Are these parts 'bike specific'???
Surely there are standard sizes, or do most bikes have different shapes to them. Obviously i know you cant tak a piston from a 125 and use it in a gixxer thou' But more along the lines of a superdream 250/400 into my 350? The engines are very similar i believe.
Same with valves too.
Anyone know?

EDIT: actually thats silly, 400 pistons will be too big, 250 too small
Point is, can you buy pistons/valves based on size rather than bike model
____________________
First bike: 1982 Suzuki Gs 125 'The beast MK1' > 1988 Honda Cb 350's' FOR SPORT! (Good ol' oil burner!) > 2001 Suzuki Sv 650 's' Made it out of the 80's! > 1997 Honda Cbr 600f :p

[rob_scott92]

right ok, i've just checked the compression levels now.
Compression 'should' be 12kg/cm(2).

I'm currently getting a reading of 9.5kg/cm(2) on the left cylinder, and 9kg/cm(2) on the right.

Thats probably fair enough really, over 23 years and nearly 50,000 miles worth of use. I suppose it could've been much worse than that

Unfortunately i cant find anything to get the oil into the cylinders with, the funnel i have is too big and i dont want to get oil in the threads. So that'll have to wait untill later.

i know i can get some 0.50mm oversize pistons from david silvers, not sure about the rings though. Then after that i'd have to find gaskets too

Cant wait till i get some money and i might actually be able to do something with this!
____________________
First bike: 1982 Suzuki Gs 125 'The beast MK1' > 1988 Honda Cb 350's' FOR SPORT! (Good ol' oil burner!) > 2001 Suzuki Sv 650 's' Made it out of the 80's! > 1997 Honda Cbr 600f :p

[N cee thirty]

lol just converted them to psi and there a fair way down if i'm right,all that sport performance has been worn away
____________________
'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[rob_scott92]

[rob_scott92]

Right, so i've compiled a wee price list. Not as bad as i thought if i've got everything down i'd need ofcourse

* Pistons 0.50mm oversize from david silvers (the only size they have), not sure if rings are included. £15 each

*Cylinder head gasket. £25.21
*Cylinder (Base) gasket. £6.46

*Valve stem oil seals IN. £1.31 x 4 = £5.24
*Valve stem oil seals EX. £1.99 x 2 = £3.98
May aswell replace while i'm in there

Total cost = £70.89

Hopefully it'll be close to that, but if a rebore/hone is required, how much is that likely to cost?
A new cam chain on ebay is around £50, might be worth doing that at the same time i suppose.
Anyone think i've missed much out
____________________
First bike: 1982 Suzuki Gs 125 'The beast MK1' > 1988 Honda Cb 350's' FOR SPORT! (Good ol' oil burner!) > 2001 Suzuki Sv 650 's' Made it out of the 80's! > 1997 Honda Cbr 600f :p

[N cee thirty]

valve grinding paste
____________________
'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[rob_scott92]

already got some, well, my uncles got some
Also got the tool to go with it
____________________
First bike: 1982 Suzuki Gs 125 'The beast MK1' > 1988 Honda Cb 350's' FOR SPORT! (Good ol' oil burner!) > 2001 Suzuki Sv 650 's' Made it out of the 80's! > 1997 Honda Cbr 600f :p

[0l0dom0l0]

I would consider doing the cam chain but that would be dependent on the condition of the old one obviously. It might cost you £50 now, but its going to cost you £75 next time you do it as you will need a new head gasket... so in reality its only costing you £25 for the cam chain if you do it this time round.

[cb1rocket]

everything from david silver spares is plus VAT!

[Wozza]

Did you warm the engine before testing compression? As I believe this may give a higher reading.

[rob_scott92]

Yeah, i suppose i could've had it warmer but then i wouldn't be able to get the dam plugs out for it being too hot.
I left it with the choke on for a while and waited for the revs to increase, at which point i turned the choke off so it idled at the usual revs.

I may try it again tomorrow to test it with oil in the bores, so i'll take it out for a few mins before i check it this time
____________________
First bike: 1982 Suzuki Gs 125 'The beast MK1' > 1988 Honda Cb 350's' FOR SPORT! (Good ol' oil burner!) > 2001 Suzuki Sv 650 's' Made it out of the 80's! > 1997 Honda Cbr 600f :p

[Robby]

A pattern gasket set from David Silvers will contain all of the gaskets and the valve stem seals.

It is rare for piston rings to wear out on a standard Japanese 4 stroke engine, it's the sort of thing that is more common on highly tuned 4 strokes, and a service item on two strokes.

Strip it and measure before you start buying parts. If the ring end gap is ok and the bore looks ok, then the rings are probably fine - clean the ring grooves on the pistons before putting them back on it after the end gap check.
Valves could have a bit of carbon built up on the back, stopping them from making a good seal. A clean up and regrind will sort this. Leaking valve stem seals can make it burn oil.

[rob_scott92]

I've e-mailed david silvers before asking about gaskets, they said they no longer stock them
Even honda dont stock some of the gaskets, left hand engine casing gasket for one Although thats not really an essential gasket, gasket paste is fine for that.

Obviously i wont be able to order any pistons or rings before i know what size pistons are in there anyway. but i will have to get the gaskets first just so i know that i'll be able to put the thing back together.

All this ofcourse, depends on wether i can get a job/electrical epprecticeship sometime soon As i'm still at college thats proving difficult
____________________
First bike: 1982 Suzuki Gs 125 'The beast MK1' > 1988 Honda Cb 350's' FOR SPORT! (Good ol' oil burner!) > 2001 Suzuki Sv 650 's' Made it out of the 80's! > 1997 Honda Cbr 600f :p

[rob_scott92]

Aye cheers Chris , i may take you up on that whenever i do decide to do it. Although i have got my uncle to guide me, i dont really have any workshop to speak of. But thanks for the offer anyway, i could always nip your way to see how the turbo's getting on
____________________
First bike: 1982 Suzuki Gs 125 'The beast MK1' > 1988 Honda Cb 350's' FOR SPORT! (Good ol' oil burner!) > 2001 Suzuki Sv 650 's' Made it out of the 80's! > 1997 Honda Cbr 600f :p

[rob_scott92]

just a quick update for those who may be interested;

Just went and checked with some oil down the bores, and both cylinders gained approx around 15 psi each (still another 25 to go). I didn't put much oil in though so i suppose if i'd have put a bit more in it would've made it round the whole of the pistons for a better seal.

So basically what i'm thinking now is that the valve seats might be slightly worn and/stem seals aswell. seeing as they would be replced at the same time (Whenever that will be ) i'm hoping it wont be too much of a problem. As long as the valves arent knackered I dont think it'd be too much more expensive

Cheers for the info guys, been helpful
____________________
First bike: 1982 Suzuki Gs 125 'The beast MK1' > 1988 Honda Cb 350's' FOR SPORT! (Good ol' oil burner!) > 2001 Suzuki Sv 650 's' Made it out of the 80's! > 1997 Honda Cbr 600f :p