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View Full Version : RG150 Loud rattle after new piston



Jase W
15th December 2007, 18:55
I finished putting a new piston in my RG today, and when I fired it up it had a very loud rattle at idle which goes away when you start moving (or you just cant hear it). Is this normal? This is the first time i've had it running so i dont know what they should sound like. Doesnt sound normal to me. I think it may be a leak at the exhaust port - would be a fairly sizeable leak though. Whats the best way to tell?

Cheers

FilthyLuka
15th December 2007, 22:51
"could you describe the ruckus?"

or the rattle in this case.

Does it go away when you pull the clutch in? Put it in gear? rev the throttle? rub your stomach whilst eating an icecream and operating the choke lever with god knows what?

xwhatsit
15th December 2007, 22:54
I heard something similar once with a guy with an old Honda twin; the cylinders had been overbored once or twice, because of wear, and then he'd put original-sized pistons in. I read this on the net, so it might be horseshit, it seems to make sense to me, but I'm an idiot.

howdamnhard
15th December 2007, 23:02
Piston slap?:slap:

Grub
15th December 2007, 23:10
I think xerxesdaphat got it.

My post was going to say, the barrell has been bored and you've bought a standard piston instead of an oversize one.

howdamnhard
15th December 2007, 23:13
I think xerxesdaphat got it.

My post was going to say, the barrell has been bored and you've bought a standard piston instead of an oversize one.

resulting in piston slap.

Jase W
16th December 2007, 01:24
Crap. I was afraid of that. I was under the impression that it had never had a top-end done. I got the cylinder honed but neglected to ask wether I would need a std or oversize. Im guessing piston slap will eventually result in some breakage?

xwhatsit
16th December 2007, 12:06
Well, it'll root your bore again amongst other things.

Is it possible to ring that shop back up and ask them how far they honed it? I.e., did you need a bigger piston?

It's funny, you said you'd never heard it running before. I don't mean to be rude and treat you like a complete newb, but have you heard many two-strokes before? Many of them do have a kind of metallic ticking/popping noise at idle and on the over-run that disappears when you wind the power on. It's not super loud, but it is noticeable.

Sketchy_Racer
16th December 2007, 12:11
Also another thing to remeber is that quite a few RG150s have loose power valves, its amazing how many rattle at idle.

And if you know anything about motors you'll see straight away if the piston is the wrong size to the bore. easy way to check, whats the ring gap currently?

Jase W
16th December 2007, 15:37
xerxes: i havent heard many 2 strokes. this is definently a very loud knocking noise that seems to disappear once the revs are up.

sketchy: then i know nothing about motors because it seemed like a perfect fit to me, and i have no idea what ring gap is. this is the first time ive replaced a piston.

Is it likely that the piston will be fine? its cheaper to get a replacement bore than it is a piston (if the place that advertised them still has them available)

Sketchy_Racer
16th December 2007, 16:54
Before you do anything to quick, just simply get someone with a decent amount of mechanical knowledge to have a look/listen. (preferably someone with RG150 experience)

Other wise any decent mechanic will be able to tell you if the sound is 'bad' or normal.

Jase W
16th December 2007, 18:53
back to your original point though, how would it be obvious if the piston was the wrong size? it seemed a pretty snug fit when sliding the cylinder over (although once it cleared the rings it slid over without too much trouble - i had oiled the piston & bore though).

I guess its still possible that it could be a leak right at the exhaust port - i have a sneaky suspicion it might not be sealing properly. Definently doesnt sound like its coming from the bottom end anyways.

Sketchy_Racer
16th December 2007, 19:29
Generally for the RG150s oversized pistons come in 4 over sizes (as far as i know)

.25mmOS
.50mmOS
.75mmOS
1.0mmOS

If you say that the piston seemed to be a snug fit, i would think that it should be right. (although that depends on your definition of "Snug")

As for piston ring gap, If it is anywhere in the range of 0.25mm - 0.4mm that should be fine.

How hard was the piston to get into the barrel?

I also assume you know about the piston ring pins. They're there to stop the rings spinning in the grooves and jamming on the ports. did you align them?

What about the gudgen pin clips? Remember to put both of them on?

(sorry for all the silly questions, but i've seen some very experienced hands makes silly mistakes like these before)

A leak at the exhaust port wont cause a knocking, and if it is leaking at the exhaust port it'll be leaking around the whole bore. it would just cause bad running

Where in wellys are you mate?

Jase W
16th December 2007, 20:20
Yep I aligned the rings to the pins. By snug I mean it slid over relatively easily (once i got it past the rings - bloody fiddly bastards) but it wasn't sloppy (ie bore had to be square over the piston for it to slide in). Im in Petone.

I definently did put both circlips in.

Ring gap - what is that a measurement of?

I took it for a ride once I had started it (probably a bad move, i'm well known for doing silly things like that) - it rode sweet as, had plenty of power, powervalves were definently working etc. The knock also went away once the revs were up (either that or you just cant hear it).

Khaitronic
16th December 2007, 20:24
where can i get new rg piston?

FruitLooPs
16th December 2007, 22:36
Hey mate, did it sound like this at all?

http://www.youtube.com/watch?v=UCobQW2OiIU knocking noise makes me think bottom end even if it is doubtful since you reckon it wasn't bottom end.

And yeah, my RG has worn pvalve ports (not that vid, ain't my bike) and rattles like a mofo at idle sounds like a ball bearing rattling about. Doesn't thump/or thud though. Down south Oyster noticed that my bore was 0.5 oversize which isn't overly common apparently. Although the bike has high KMs so it figures.

You also probably want to take it easy for a bit before thrashing about on a new piston I would think.

Jase W
17th December 2007, 06:41
Hmm sound similar but maybe not as bad...

ill compare tonight.

tommorth
17th December 2007, 17:45
if you dont mind whats the piston rings and gaskets worth for a rg?

vamr
18th December 2007, 00:01
if you dont mind whats the piston rings and gaskets worth for a rg?

Around $90-100 for the kit which includes piston, rings, pin and circlips then add another $50-60 for the headgasket.

Jase W
18th December 2007, 05:27
more like $180-200 for the kit, $40 for the base gasket and $90 for the head gasket (just re-use the old one).

vamr
18th December 2007, 09:32
more like $180-200 for the kit, $40 for the base gasket and $90 for the head gasket (just re-use the old one).

Hrm, was going off the price for a kr150 back when I had one :P

ajturbo
18th December 2007, 14:42
ummm KR150... is NOT a RG150....

the KR's are a lot cheeper....

but i would really be check your power valves NOW....

DO NOT START the bike or even kick it over untill you KNOW they are ok....

bring it around here and we can have a look for you..
:beer:

Jase W
18th December 2007, 20:35
powervalves are sweet. well they were when i put them in anyways. i'll have to wait till i get my car sorted & a towbar fitted before i can take the rg anywhere, im not too keen to start it.

ajturbo
18th December 2007, 21:15
did you put them in the right way????..
:bleh:

Jase W
19th December 2007, 07:25
they only go in one way...

ajturbo
19th December 2007, 20:45
thats what you HOPE....

but i managed to put them in the wrong way...:doh::stupid: lucky i noticed...

Jase W
19th December 2007, 21:39
hmm.... im pretty sure i got them in the right way eh. i'd imagine it would be a big crunch and not much else otherwise - the bike still goes fine (not that i should be riding like that with a new piston - but im a silly bugger), powervalves seem to be doing their job fine eh. i think after xmas/ny is gonna be when ill have time to sort it out, for now it can sit. ive got till may to get it into fighting form.

Gubb
20th December 2007, 21:10
It better be going by Saturday.

I wanna have a go.

Jase W
21st December 2007, 06:28
Haha nah mate itll have to wait - if we're lucky ill have it ready before the bdo so ill chuck it on a trailer and bring it up (bugger riding it up, been there done that).

Jase W
6th January 2008, 13:39
Update: Ive pulled the pv's out again - they are sweet (exactly as they were when they went in). I decided to temp fate and start it again so that I could make a video of it - http://www.youtube.com/watch?v=ZLZg5gZublA&feature=RecentlyWatched&page=1&t=t&f=b

One guy commented and said it sounded like big end. Hope not.

Does that help anyone?

Sketchy_Racer
6th January 2008, 16:06
ooooooooOOOohh... Thats not a piston knocking..

I would suggest you pull the barel off (dont take the head off, saves a head gasket) and check for any free play. Unfortunatly I think the guy could be right about it being a big end or a main bearing

tommorth
6th January 2008, 18:38
it sounds sick id do what Sketchy_Racer says
you didnt drop somthing down the plug hole?

FruitLooPs
6th January 2008, 22:59
It sounds to me like you have the same problem Magua had with his bike, thats his in the clip I posted up earlier.

here is his thread about his bike, it's pretty old but might provide some insight.

http://www.kiwibiker.co.nz/forums/showthread.php?t=28931&highlight=rg150


On another note, just got my RG sorted once again - one pvalve was stuffed, new tyre chain and rear pad. Mm was fun on the port hills though :devil2:

*edit* a quick scroll through his thread, yeah his big end was shot and crank etc. Hope thats not the case for you, but it sure does sound like it to me :(

Jase W
7th January 2008, 06:40
ooooooooOOOohh... Thats not a piston knocking..

I would suggest you pull the barel off (dont take the head off, saves a head gasket) and check for any free play. Unfortunatly I think the guy could be right about it being a big end or a main bearing

How much play am I looking for, and in which direction (I assume moving the rod side-side to see how much it moves?).

I was pretty careful, made sure that it was all covered so that nothing could fall in, if there happened to be any loose bits around (ie piston circlips).

oyster
7th January 2008, 09:53
In a GP bike like an RS 125 the big end has a life of around 3000km.
You expect that, 45hp and 12000rpm all day. On an Rg its still 12000rpm but only 60% of the power, but this means RG's have a big life that's still quite short. For racing probably 6000km, on the road 15000km. All depends on oil quality, condesation ingress (very common) and the thrash factor.
On a race Rg a big end goes from quiet and performing perfectly to complete blow up in a tenth of a second. On the road often they die slowly and I've seen (and heard) plenty on the way out. Of course a good thrash up the motorway or tack and it'll go bang big time. Will wreck casings, barrell, the lot.

To check the big end the easy way take the exhaust off and the alt cover. Turn the crank back and forth and if you can detect the the crank moving but (momentarily) the piston not. (Look up the exhaust port).
The full check means barrel off and very carefully feel for radial movement.
Axial no problem, factory setting 0.4 from memory
Any more that 0.02mm radial can be felt, and if it's there, it's stuffed.

Only answer is new big end.

Jase W
8th January 2008, 07:21
Cheers for that mate. When the weather fines up i'll give it a go. When I had it apart for the piston, there was a tiny amount of side-to-side movement (Axial?). Probably within the tolerance you have specified there. Im pretty sure there was bugger all (if any) play when rotating the crank (Radial?). Of course I wasnt actually checking anything so chances are there was a bit of play and I didnt notice it.

Is it worth trying to do a big end myself (for the learning factor etc), or is it one of those jobs that is better to let the professionals handle, or should I just replace the whole engine (anyone got a good one for sale?)?

Thanks again to everyone that is helping me without actually seeing the bike!!

Jase W
10th January 2008, 15:40
Ok i've just a had a look up the exhaust port while turning the kickstart (dont think it matters if I do it this way?), there is definently no delay before the piston moves once there is resistance in the kick lever. I did notice some faint vertical scratching on the side of the piston though... dunno if that matters.

Is there anyone in the wellington area with experience that could come around and have a listen/play? My video does get the general gist of it across but I guess its always easier to diagnose in person...

ajturbo
10th January 2008, 21:37
think you should be asking sketchy....:confused:

Jase W
11th January 2008, 22:51
Im going to pull the engine out tomorrow as its going to need to be pulled apart anyway. Maybe once I have the barrel off there may be some more clues as to what the noise is.

Spuds1234
12th January 2008, 00:08
Sounds like my gs250 when it shat a big end bearing.

Apart from that Im no mechanic so I dont know shit.

ajturbo
12th January 2008, 06:00
Im going to pull the engine out tomorrow as its going to need to be pulled apart anyway. Maybe once I have the barrel off there may be some more clues as to what the noise is.
hey... when you have pull all apart, give me a call..
0274 595830....
i'll see where i am and could pop over... and stand there strocking my chin and saying ..
hymmmmmmmmmmm....
Oooo look there is that thingy bit!
where's ya beer?
now THAT doesn't look good... but ya sister does!... (hope she looks good!)
well.. at least your tyres are black... not like some of the trail bikes that i have seen that are yellow/blue/orange..ghey...
and ...

Jase W
12th January 2008, 09:54
lol ok ill keep that in mind mate, cheers.

Right now I need to find something suitable to insert through the swingarm pivot to stop it all collapsing when I pull the bolt for the rear mount.

Gubb
12th January 2008, 14:40
Will your cock do?

roadracingoldfart
12th January 2008, 21:58
I dont like the sound that engine makes at all.
Did you check the gudgin pin was the same diameter as the rod end and the same as the piston pin diameter ????
If they are ok i think a big end has just gotten bigger :gob::shit:

Ixion
12th January 2008, 22:01
Um, I know this is a REALLY silly question, and please don't be offended, but you *did* put the little end in, didn't you ? Just I know someone once forgot it ! (No it was NOT me !)

Jase W
14th January 2008, 06:37
Yes I put the little end in. As far as I know it was the correct size - it was part of a kit and it fit.

Gubb
14th January 2008, 17:03
Will your cock do?

Yes I put the little end in. As far as I know it was the correct size - it was part of a kit and it fit.

:lol::lol::lol: