Exhausts

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knackeredMk1
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Exhausts

Post by knackeredMk1 » 25 Nov 2009, 18:01

The original exhaust systems are very quiet, particularly on Mk1/2. They are also quite restrictive. Most owners replace both expansion chamber and silencer with aftermarket items. This releases a little power (compared to the probably heavily gummed up original) but does reduce weight by ~2.5kg as the originals are very heavy. Mk1, Mk2 and generally Mk3 are directly interchangable.

Most owners go for aftermarket exhaust systems to 'improve' the sound of the exhaust also the fact that Honda don't sell the silencers and some of the expansion chambers anymore.......

To be honest if you are still running a stock exhaust on your bike it probably needs replacing or at least cleaning. Two stroke exhausts build up carbon/oil gunge and this restricts gas flow, particularly in the silencer. Unfortunatly the original fit silencers are really difficult to clean and the Mk1/2 are pretty much impossible. All expansion chambers can be cleaned to an extent but this is a difficult and sometimes dangerous activity. It involves large quantities of highly concentrated caustic soda which is very corrosive to flesh and particularly eyes. (Find other posts on the Web to get instruction). Often the best way is to buy new kit.

There are several aftermarket suppliers - DEP, FMF, ProCircuit, RSV, Mugen, Skill ................ All of which supply much the same product with much the same performance. DEP is a UK manufacturer, the most popular, and the easiest and cheapest to get hold of. They do Mk1/2 (that fit Mk3) and AR pipes + two silencer versions. DEP pipes nowadays have the thinnest nickel plating and do tend to rust the quickest. FMF is available in the UK but this is 'old stock' as, to my knowledge, they are not made any more.

ProCircuit pipes are available in the UK by special order and they do 2 pipes; one for the Mk3 and one for the AR + a common silencer. I believe the Mk3 pipe + silencer will fit the Mk1 & 2 but I can't be 100% sure as yet. The pipes and silencer are more expensive than the competition but the pipe is better made and coated, and the silencer internals are stainless steel so don't corrode. The pipe is fitted to the barrel with springs rather then studs and comes with an adaptive flange to enable this and reduces potential damage when the pipe does hit the ground.

Skill still make a wide range of beautiful pipes but some are very expensive and all have to be imported from Japan. You can choose between mild and stainless steel construction for both pipes and silencers.

In the main the other manufacturers no longer make CRM exhausts and their pipes come into the UK already fitted to Japanese bikes.

Some owners have fitted CR pipes but they have had to change the way the pipe connects to the barrel as the CR uses springs and the CRM uses studs/bolts as ProCircuit.


Current approximate prices and quality (Best first). (My opinion only April/2012) -

Pro Circuit Platinum. Expansion chamber (Nickel plated) £220, 304 silencer (Stainless steel inlet and tail pipe) £106, delivery for the pair as special order only £12.

FMF Gnarly. Expansion chamber (Nickel plated) £190 (Old stock only as no longer made). Silencer not currently available.

DEP. Expansion chamber (Nickel plated) £185. Silencer £75.

I would not be able to tell the performance of each apart but I believe the Pro Circuit is better made than the others and the FMF is slightly better made than the DEP. The thickness of the Nickel plating also runs in that order.

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Re: Exhausts

Post by knackeredMk1 » 12 Feb 2012, 13:37

Mk1, Mk2 and Mk3 exhausts have the same exhaust stud arrangements. The AR does not. See photos below -

Mk1, 2 & 3
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AR
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The original Mk3/AR exhausts tend to have longer exits from the expansion chambers so the silencer has a shorter entry pipe. I use the word 'tend' here because it seems not all Mk3 pipes are the same :roll: . Because of the different stud arrangements some aftermarket AR pipes won't fit the Mk3 without some modification. This particularly true of the DEP pipe that has a 'welded in' collar (rather than a loose one) that has little meat on it to allow enlargement of the holes. Apparently Leisure Trail recommend use of Mk1/2 pipes on Mk3s. These do sometimes need to have a short section cut off the tail pipe that comes out of the expansion chamber to the silencer but sometimes not :? . Mk3s with this setup sometimes need rejetting as they get a flat spot in the carburation.

Thanks to Sorbs for the above information :BB .

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Sealing the Expansion Chamber to the Silencer

Post by knackeredMk1 » 24 Mar 2012, 21:33

The original way of sealing the CRM silencer to the expansion chamber is cobby and doesn't always fit properly if you use an aftermarket exhaust or take the silencer off a few times. I tried using glued thick heat shrink tubing but it doesn't last too well.

I've found that the rubber seal used on CRs works best. There is one for CR250s and the latest 125s that does OK, but I find the one for late 80s 125s works best as it is tighter. Part number - 18365-KZ4-000. They are about £10/11 and fit really well to stop the exhaust blowing and gunge seeping out.

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