MK 1 Powervalve Question

flying scotsman · Post by **flying scotsman** » 09 Mar 2006, 18:14

I've noticed a rattling noise on my MK 1 similar to that of other folk, which is prominent if in too high a gear etc. I've taken the exhaust off and noticed that the powervalve flap has slight movement up and down like the splines on the shaft /flap are worn. I noticed on the reciepts I got with the bike that the engine had been rebuilt by Leisure Trail a few years ago and that they had charged for\" machining\" the powervalve. Does anyone know what this repair would have consisted of, and do you think the bike is ok to run with this type of wear.
Thanks in advance.

Steve

lee_p · Post by **lee_p** » 15 Mar 2006, 17:34

Hi Steve rebuild the top end a while back and my power valve has movement in it, i would say in my own personal opinion that the valve is that small you wouldn't hear it rattle over the noise of the engine. The power valve is on a master spline onto the shaft and then there are two bushes that hold it central, bit of a bitch to get out but if you warm the valve with a heat gun it helps. Does the valve move correctly when revving the engine, are the cables adjusted correctly, power valve motor partially seized. Have heard the noise you are on about, just knock it down a gear and hit the throttle.

There seems to be a few posts regarding crankshaft balance making a noise which would be loud enough to hear.

Lee

edarter · Post by **edarter** » 16 Mar 2006, 13:06

I would go the balance shaft route..... I had a similar pinking thumping type noise under load if in too high a gear, then when getting an MOT the garage said main bearings were going, but during strip down it turns out the balance shaft is worn (main bearings proved to be fine).... you're probably looking at the same thing. Though the good news is that it's not an engine out job to sort... you need to throw about £150 at it in parts to get it sorted.

Bargos · Post by **Bargos** » 16 Mar 2006, 19:09

The balance shaft can be removed and visually inspected with the engine in the frame. Im sure its posted elsewhere on here as I cant remember whether the clutch basket has to be removed or not to do so.

d5aul · Post by **d5aul** » 16 Mar 2006, 21:00

Bargos wrote:The balance shaft can be removed and visually inspected with the engine in the frame. Im sure its posted elsewhere on here as I cant remember whether the clutch basket has to be removed or not to do so.

Yes you can remove the Balacne shaft with the engine in the frame, you do not need to remove the flywheel unless you are changing the bearing but you will need to remove the clutch basket as this half covers the Balance shaft securing nut!

You will possibly notice that the bearing surface on the shaft (next to Balance weight) will have wear marks in it, if you have the marks, the shaft will need replacing.

The following link will give you an idea of what is involved.

http://www.offwidth.co.uk/bike/crm_rebuild/

d5aul · Post by **d5aul** » 16 Mar 2006, 21:09

If you do need to replace the shaft, you may be interested in a method I used to fix the problem, I posted the following on a previous post a while ago!

After paying out the £80 odd for a new balance shaft, which started rumbling after about 600 miles, I managed to find a way of repairing the old shaft, this has now done about 3000 miles & is still as quiet as a new shaft!
I contacted my local Bearing supplier & purchased a bearing sleeve, which measured 25mm outside diameter, 25mm long & I think it was 21mm inside diameter, cost about £3. This is basically a tube with a ground & hardened surface!
I then contacted a local small engineering firm with a Centre lathe, they were able to hold the Balance shaft in the lathe & machine the old bearing surface down to suit the bearing sleeve, they also had to machine down the 'Gear' end slightly to allow the bearing to slide over.
They commented on the fact that the machining was particularly difficult due to the hardness of the old bearing face & the fact that the shaft, by the nature of its purpose, was ‘considerably out of balance’ which stopped them running the lathe at the ideal speed.
The sleeve was then fitted using some bearing Fit Locktite, the sleeve had to have a chamfer ground on the edge as it fouled on the Engine casings.

smb2200 · Post by **smb2200** » 16 Mar 2006, 22:37

You can tell if it's the balance shaft as you will hear a \"rotary\" whine which speeds up when you rev the engine. It's quite high pitched, but you will hear it even under no load.

If you hear a \"rotary\" whine thats quite deep and rattly (if thats a word) and it's likely to be main bearings. You can hear this under no load also.

I had to replace both.

The rattle i suspect though is the piston bouncing from side to side (or front to back) cos you are labouring the engine. Two strokes don't like being worked at low-low rev's because of the size and length of the piston's skirt it will \"bounce\" in the cylinder. You dont want to do this too often.

Only my opinion, unless someone backs me up...

flying scotsman · Post by **flying scotsman** » 16 Mar 2006, 22:42

Thanks for the replies guys, I was planning on using my bike for enduros this year and seeing as i've spent a small fortune on her already on suspension bearings etc , I thought I might try and coax her through the year and do a strip and inspect in the winter if I don't blow the motor up beforehand(would a worn balancer cause terminal damage?). The repair option sounds a good idea. Do you think that the same engineering company would be prepared to repair mine if it needs done as there is nobody up in my neck of the woods that I would trust, cos all the good engineers I used to deal with are retired/passed away.
Will post pics once I refit my exhaust which has just been painted with some lovely NATO heatproof paint which I won on e bay.

Cheers

Steve

smb2200 · Post by **smb2200** » 16 Mar 2006, 22:50

Running the bike with a \"slightly damaged balance shaft wont hurt it no. I asked the same question to leisure trail. It all depends how damaged it is really. It's easy to inspect though as d5aul mentioned.

It all depends whether you can stand the whining noise really. I didn't like it personally so changed it anyway, am looking to repair the old one though as mentioned. I like to hear a smooth running bike myself

Good luck with it then, look forward to the pics.

Cheers

d5aul · Post by **d5aul** » 17 Mar 2006, 19:25

flying scotsman wrote:Do you think that the same engineering company would be prepared to repair mine if it needs done

I could always ask, its a company we use through work, it may cost you a few quid, I think I paid about £20.

smb2200 · Post by **smb2200** » 17 Mar 2006, 20:01

I'd be interested aswell d5aul if you dont mind finding out for the spare damaged one ??

SMB

edarter · Post by **edarter** » 21 Mar 2006, 13:05

yeah - LT said the same to me - it won't damamge the engine until the bearing lets go (if it ever does). I'll be interested in the repair option at some point as my balance shaft has slight marks on it (found out on a recent strip down and rebuild, but no cash left to change it as about another £130 with bearings etc)

burnout1 · Post by **burnout1** » 25 May 2007, 08:08

I had an old XR-250 ('83 i think...) and it had done the balancer shaft bearing , i took it to local mechanic and he told me it was only to stop vibration when your sitting at the lights? They just removed it and it cost me $50 labour . The bike was instantly more responsive and revved out wickedly (I rode it hard for about 2 years with shaft removed).

Does anyone know if you could do the same for a CRM?

Post by **knackeredMk1** » 25 May 2007, 10:21

I would imagine that you can but don't know. You will certainly get a better throttle response but won't you lose some of the low down torquey mud rippling tractability that the CRM is famed for?
There again that might not be neccessary in NZ

lee_p · Post by **lee_p** » 25 May 2007, 20:45

After replacing my bearings and doing as dpaul mentioned the bike was totally different, smooth throttle response, crisp revving, more power and most of all it stopped drinking 2 stroke oil(1/2 tank of oil to 100km) which has now gone to at least 200km.

The shaft is there to counter balance the engine so that when piston hits tdc the weight should be facing backwards, didn't need to remove flywheel when i replaced mine knocked roller out from clutch side

Lee