Balance shaft removal

[Mudfacetony]

Has anyone removed the balace shaft and had the holes plugged up? If so, was it difficult to do/cost lots of maney? And what was the vibration/performance afterwards?

[Jonorow]

I know it has been done, by someone on here but cant remember who it was. It might have been Nabz? just do a search, it should come up somewhere.

[AlanH]

One of my friends did this to his AR a few years ago when he had one. He did the work himself so it just cost time, gaskets and consumables. This is what he said about it:

The mod's worth around 5 bhp and the bike feels noticeably quicker and more responsive - but it is vibey. The vibes aren't too bad - it just feels a bit more like a crosser and less smooth and civilised.

He didn't regret doing the mod and didn't put it back to standard so it can't be horrendous without the shaft. Although 5bhp would come in useful, I think I'll stick with the smooth nature of the bike as it is.

[Eddie Evans]

The mod is simple.Drain the water, block the 2 stroke tube(unless you are a bodger like me) Open the clutch case, remove the clutch, remove the balance shaft sprocket and replace it with a suitable spacer. The centre part of a wheel bearing is about the right diameter and width. This way the shaft will not be turning and there is no need to block the holes.Tighten the nut back up and re assemble.
I did this for a friend and gave it a test ride after.There was a bit of vibration when cold which eased a bit as the bike warmed up. I felt that I needed to carry a few more revs to stop it from stalling. This may have been due to a different set up on his bike.
I wanted him to give the bike a real good test on a trail ride but he felt he had lost confidence and was unwilling to ride it far and I was too busy at the time.
My concern about the mod is that some of the low down CRM anti stall is lost but I did not take the chance to put it to the test.
So it will cost nothing but time if you do it yourself.

[knackeredMk1]

There is no way it is worth 5bhp . All you are doing by having one is drive 2 bearings.

Should think there is quicker throttle responce but a bit more vibes.

[Mudfacetony]

Eddie / Alan, thanks for the quick reply. Eddie's idea sounds perfect in that you still keep everything in place and it is easy to un do. It will also save me getting spacers made (a guvvie job at work).

As I've got 4 CRM's and this one is for rally racing I think I will give it a go. this would be for my rally events so a bit of vibration is OK, and it saves me nearly £100 on an exchange shaft. It might even get me a bit more power (5bhp as Knackered says is a bit much)

[AlanH]

I thought 3bhp would be a more likely figure. It's not just the bearing losses, it's a counterweight flailing around inside the case and also gear friction losses where it meshes on the primary drive gear (I presume that's where it's driven anyway).

[knackeredMk1]

Whatever the figure (and AlanH is right about loses in gears ) the Japanese recommend taking the balancer shaft out when making a 'racer' CRM.

Still recon ~ 1-2bhp absolute tops. But worth doing in Tony's case.

[knackeredMk1]

In a Japanese 'CRM250R Hot Tune Tips' (Mk2) they -

Fitted a Mugen silencer and expansion chamber, removed all the baffles and snorkels in the airbox and replaced the filter, removed the balancer shaft and oil pump, matched the ports and did some moderate reprofiling, skimmed the head and profiled the powervalve.

Guess what increase they got ..........................



3.5bhp. = 12.8% over completely stock.

Which is actually quite good at the wheel whilst managing to keep the low & mid range the same.

In theory you can get 6% increase in power by upping bore from 66mm to max 68mm due to increase in capacity.

[Mudfacetony]

[quote="knackeredMk1"]


In theory you can get 6% increase in power by upping bore from 66mm to max 68mm due to increase in capacity.[/quote]

What piston do you use for that as it sounds appealing

[knackeredMk1]

68mm is the largest bore size you can get for a CRM250 piston - makes 262cc.

I've got a Wiseco piston of that size that I was keeping for some years ahead when I've rebored mine a few times but I need the cash for another project. You could have it at cost price .

[Mudfacetony]

How much do you want for it and does it have rings and small end?