Compression test results...

[Mr Hammers]

And the winner is..........not this one.

That says top end rebuild, in great big neon letters, to me.

Hopefully someone will tell me different. Please. Please someone tell me different!

[----]

What bikes it?

Have you got a workshop manual for it?

Whats the compression supposed to be?

Have you tryed putting a little bit of oil into the chamber then repeating the test to see if the results change?

It's all in the details man
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DRZ-400sm

[Rockhopper]

What bike? What did the other cylinders read? Did you do a wet test?

[Mr Hammers]

Thanks, both.

Rockhopper: As below, only one, no, but now yes.

justmetoo125;

NSR125RM (JC20E)

Yes (thanks, alains!)

It says 1,000 +/- 20 kPa (10 +/- 2kg/cm2, 142 +/- 28 psi)

No, i hadn't put oil in. Good thinking!

But have now, and it now says this!

So now it looks like it's a little lower than it should be, but altogether a lot healthier. So, could this possibly mean i.....i don't need a rebuild after all..?

Thanks for the renewed hope!

[KawasakiAndy]

The link is broken so i cant see, but if it has gone up now, it means your piston rings have gone. Simple job on a 2-stroke Single

[Mr Hammers]

i think the link is working now, but anyway, it's gone up to 100 (or 7). That's up from the dry test at 35 (or 2.5).

Bugger. And for a moment there i thought meant it was going to be ok.

Is it that simple? i've replaced rings before, but only in situ. i'm worried the engine will have to come out, although i can sort of see everything, i'm not sure how difficult it'll be to get to the head and all the nuts and bolts, because of the frame in the way.

Have to say i'm disappointed it's going to need new rings, but i am happy that at least once they are in i don't need to worry about them for a good long while

[----]

If the compression went up when you put oil into the cylinder,then it' almost sure to be the rings.
The oil seals the rings which makes the compression go up,once the oil has seaped past the rings the compression should go back down to your original test...

Piston rings are really easy to change on a 2t,and should be no problem at all doing it with the engine in the bike.
Have a good check of the condition of the bore when you strip it to make sure it doesnt need a rebore...
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DRZ-400sm

[salty21]

odds are if your compression is that low the piston is ready aswell you may aswell change it while you have the cylinder off along with clips bearing and pin, i think it all comes to about 60 quid IIRC, im sure alains will supply you with a parts list with all relevent numbers and prices
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04 NSR 125(sold) ---- 03 CBR 600rr(sold) ----90 pan euro ST1100 '' ----02 CG 125
94 CB400 Super Four ---- 2000 VTR SP1 (sold) ---- 08 ninja p8f(sold, meh) ----05 CBR600rr

[Kickstart]

Hi

Lobbing a bit of oil down the bore helps the rings to seal for a short time. Hence doing a compression test like this helps to nail down if the problem is rings or valves on a 4 stroke.

With a compression reading of 35psi the bike would almost certainly not even manage to run.

Are you doing the test with the throttle wide open?

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Mr Hammers]

Ok, barrel is off, piston is out.

The bottom ring was in 3 bits, worrying i can't find the third bit..hmm... top ring was was ok, but as you can see in the pics, it looks like the 3rd bit of the ring went walkabouts inside the cylinder. Hopefully it's disintegrated enough not to be a problem if any of it fell into the crankcase.

The bore could be better, but doesn't look too bad, i think. And to be perfectly honest it will have to do. i've thrown more money than i can afford already, so a rebore would be good, but is impossible right now.

i was hoping the piston would be salvagable, but looking at it, i'd guess it's a bit too wrecked.

So, new piston and rings then.

What is annoying is that i was looking forward to the family being away for a couple of weeks so i could go out riding all over the place...instead i'm spending the whole time fixing the dang thing instead!

Here am the pics;

Inside barrel
Inside barrel 2
Piston damage
Piston damage 2
Top of piston
Cylinder head

Thanks, everyone.

Edit: Just a thought, while the barrel is off, anyone know if it's worth polishing up the ports, piston top and cylinder head? Or would it not make enough difference for the effort?

[salty21]

why polish something your gonna throw away lol(piston), but its always worth polishing the head
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04 NSR 125(sold) ---- 03 CBR 600rr(sold) ----90 pan euro ST1100 '' ----02 CG 125
94 CB400 Super Four ---- 2000 VTR SP1 (sold) ---- 08 ninja p8f(sold, meh) ----05 CBR600rr

[alains]

you can DIY your head :
- clean the squish and polish it with belgom alu
- buy a sheet of waterproof sand paper grade 200-280 & 400 (1 of each)
- on a pefect flat & hard surface put the bigger grade sheet then with your head make several pass in "8" without pressing too much until your contact surface is clean of any marks . it could take from 5 to 15 mn , then do it again with the thin paper

about your barrel , pass your fingers inside and if you feel scuff even small do not use this barrel , also check the bar between the 2 exhaust windows , it must be perfect because this point is often the origin of broken rings . if not ok , have a cylinder-piston kit (£180 with all spares needed to rebuild) . if ok pass begom alu to polish a bit then change piston and stuff (warning : look your barrel size and buy the same piston letter as the barrel (letter is hammered under the exhaust port)
see ewemple https://www.geneva-racing.ch/~alains/lettre.jpg (letter is a "E")
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the worst day fishing is better than the best day working

[Mr Hammers]

Thanks, alains. i'll find out the barrel letter and double-check the condition tonight, but i'm pretty sure it's not scuffed, but i'm not sure about the bar bit. i really hope it isn't too damaged as i really can't afford a rebore...it'll have to sit there for months until i can (not quite what i had in mind when i bought it).

Never heard of begom alu, is it similar stuff to SolvolAutosol..?

Once i've found out all of the above, would you mind sorting out a parts list for me, alains? Much appreciated!

And no, salty, i wasn't talking about polishing the damaged piston... because... well... that would be madness!

[Kickstart]

[Mr Hammers]

In that case then, Keith.... i can afford a rebore, but i can't afford to fix it

[alains]

a rebore & replating cost about the same as a new cyl-piston kit (£120 inc VAT) . you said you find the letter , what letter ?
curiously A to D piston are affordable but a "E" is much more . some aftermarket are good but they have different references , so i need your letter . then afterwards i will make your list with honda refs
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the worst day fishing is better than the best day working

[Mr Hammers]

Sorry, alains, can't tell you what the letter is yet as the cylinder is at home (and i'm at work). But i will find out tonight and let you know, thank you.

i'd love to do a complete cylinder and piston replacement, but (and i hate to go on about it..) i really can't afford it right now. i can't really afford new piston and rings either tbh, but i'll have to take the chance, as i can't afford to keep driving the Rover to work either, as that's costing a small fortune too..

Edit: Something i meant to ask before; i discovered that the CDi on there is a CI572. Am i right in thinking that this is a UK unit, and is better for high-end revs than the CI626 which has a flatter curve? But is still actually unrestricted..?

[alains]

have a look when at home . CI572 is the correct CDI on NSR 1989-1992 as your bike is . in 1993 they change the middle stand to a simple side stand and they include a security stand , and consequently they modify CDI's . so it's OK for you
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the worst day fishing is better than the best day working

[Mr Hammers]

Good news! It is a C.

And, purely out of interest, do you know what the 235, P and 2M mean?

[alains]

the C near the 235 has no relation with the size , it's a serial mould number . after having been coated the barrel receive a letter or a sign from the worker and then the exact size hammered , as you see on the right . so your size is 53,966 to 53,970 mm . if you can find a forged piston kit of this size go for it
several are on the market such as technium or woëssner . the kit include rings , pin and clips for a cost around £75 . i've never investigate UK shops for that but we have plenty in france or germany . woëssner are sold by bihr-racing
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the worst day fishing is better than the best day working

[Pete.]

[Mr Hammers]

Ok, i started drooling when looking at cylinder and piston kits and all things racy, and it started getting pricier and pricier and a bit out of hand, so instead, i've decided i'm just going to stick in a standard piston and ring kit for now, and then in another 6/7k miles i'll do the whole thing properly, bottom end as well.

The kit, plus top end gasket set came to £48.01 in total, and that was from motorcycleproducts.co.uk. Quite reasonable, i think.

Had another look at the barrel and i can't see or feel anything potentially terminal in there, so i think it will do for now and at least get me on the road asap, and later when i have more money (from saving on all the petrol i usually put in the Rover every week) i can shell out on better quality bits.

With a bit of luck, the kit and the jets will be here by Friday, so i can do the rebuild at the weekend. Might even take a day off on Monday to go riding somewhere. Gotta eat those running in miles up!

Many thanks all for the help and suggestions, i'll let you know how it went (if you're interested )

Cheers!

Edit: Foi d'mer! They're out of stock and not getting any till the end next month!

And so the search begins again..

[salty21]

give these a bell, you should get all parts well before the weekend, i use them for all my parts for the nsr, top notch service imo

www.davidsilverspares.co.uk
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04 NSR 125(sold) ---- 03 CBR 600rr(sold) ----90 pan euro ST1100 '' ----02 CG 125
94 CB400 Super Four ---- 2000 VTR SP1 (sold) ---- 08 ninja p8f(sold, meh) ----05 CBR600rr

[Mr Hammers]

Thanks, salty, i called them this morning, but they're too expensive for me. They want £106 for a piston kit and top-end gasket set (genuine Honda parts), More than double what motorcyleproducts wanted, and twice as much as i can afford.

So unless i can find pattern parts today (and somewhere that also does next day delivery), it looks like i'm going to be off the road for yet another month.

Deep breath...count to ten...]

Edit: Yay! Found one! BikepartsUK.com has one, and the kit and gasket set are even cheaper, total of £38.45 inc p+p. Not bad!

[Kickstart]