Knackered's Project - Highly Modded Mk1

[knackeredMk1]

Clutch basket anodised and fitted

[knackeredMk1]

Finished the engine. Need to start it, adjust oil & fueling and finalise electrics as far as the engine is concerned. I'd forgotten how much of a pain the CRM is to work on compared to competition machines . You have to take lots of stuff off to adjust something that should be easy......................



On the other hand the 'new' kickstart looks and fits better than the original

[knackeredMk1]

Couldn't resist slapping it together to see how it will look . I have wrapped all the electrics in corrugated plastic tube. Still got a long way to go with the fit and adjustments everywhere. Don't be suprised if it's not finished in four weeks time

[knackeredMk1]

Fitting went much smoother than I had anticipated. So now running in.

Started with 50 pilot and 155 main. Now using 48 pilot and 135 main. Stock for Mk1 is 45 pilot and 132 main.

Slightly disconcerted at the lack of smoke coming out the back, except on over run . (Really smokey on startup especially if has been standing for a while.) Pulls very well at low revs and on through the range without the 'hit' of the 125s I have been more recently owned.

[knackeredMk1]

Thanks to all the people who helped on this project with advice, support and experience.

To those on this forum but especially to Slider and Gwyn.

To those at Worcester College of Technology but especially to Steve Dixon, John Emerson, Mike Moore & Matt Harwood. Who gave assistance, advice and tolerance well above the call of duty.

To Redditch Shotblasting, Kevin Bancroft and Racespec, but especially to Tom, Jerry and Kev at Leisure Trail who handled some decidedly unusual requests with professionalism and good humour.

[knackeredMk1]

Have had a go on a few CRMs since finishing the project and several have been on my bike.

There are several things that are very noticeable -

It is taller - ~1 inch seat height (a fraction taller than a Mk2 but shorter than an enduro bike).
It is more 'flighty' in steering - CRMs are generally very stable (almost too stable) but this changes direction much more quickly. (Good or Bad - I prefer it this way)
Narrower - Knees closer together and more control
Rides more firmly damped/less sloppy - Your backside feels more of the bumps when sitting down but the bike skips across obstacles better than before.
Brakes have much more feel/power - This is a personal and age (of bike) related thing.
Throttle response is much quicker - whether this is due to the changes made or just that it's newer (Bit of both I think.)

I wanted to make a more modern version of the CRM but not turn it into a roadgoing MXer. (Sort of halfway between the old CRM and an enduro bike.)

I think it has hit the mark .

[knackeredMk1]

This has been talked about elsewhere on the site but it is worthy of mention here.

Stock dry weight of CRM250 Mk1 123kg. Knackered's project weights 112kg with all oils and 1/2 tank of petrol. The weight reduction has come through -

Approx weights as I remember them, though I did not weigh many parts.

Tank - original v CR125 = -1.5kg
Got rid of lots of useless brackets holding on e.g. rear brake fluid reservoir, whole section from back of sub frame for lights, helmet lock ........ (saved a lot of weight)
Got rid of whole rear brake light switch and replaced with HEL pressure switch.
Replaced whole rear brake master cylinder, pipe and reservoir with one from a CRF.
Replaced steel brake pedal with ally one from CR500. = ~-300g
Replaced front brake master cylinder and also calipers front & rear with CRF.
Replaced steel kickstart with ally one from CR250 = ~-300g
Replaced whole exhaust system FMF/DEP = - 2.5-3.0kg
Got rid of carb heater.
Got rid of coolant overflow tank and piping.
Got rid of some wiring in the loom and relays = -250g (just weighed)
Got rid of sound proofing in air box side panel = -200g (just weighed)
Got rid of all original rear lights = a lot
Got rid of indicators + brackets (although could put back as have all wiring in place).
Replaced speedo.
Got rid of speedo drive and cable.
Got rid of chain guard on swing arm.
Got rid of whole oil level sensor system.
Ally rear sprocket.
Got rid of rear foot pegs (put in plastic bolts to save threads) = -450g (just weighed)
Replaced carb = -135g
Replaced clutch basket = -40g
Replaced air filter frame = ~-100g
Stainless steel brake hoses are much lighter than original.
Got rid of side stand switch, cover etc.
Replaced steel bars with ally.
No tool box and tools.
CR seat is lighter than the CRM one.
I suspect lighter tyres.

Rear shock and front forks are approx 500g each heavier than original. There is also the sump guard and hand guards to put in here.

The biggest areas to reduce weight are the exhaust system, the tank and getting rid of the very bulky rear lights and supporting framework.

[knackeredMk1]

Now fitted:

'PowerNow' from 'Scaryfast' (it's almost embarrasing with those names ). A horizontal vane across the upwind side of the carb to decrease turbulance of air flow at small throttle openings and give better throttle response. They also do one for the down flow side of the carb. Seems to work quite well but needs a drop in pilot jet size to 45. Boyesen and another company do similar things but not for a 33mm PWK.



Got a reserve section in tank through fitting an XR600 petcock (Honda Part no. 16950-KT0-831). Reserve ~ 1 litre.

[knackeredMk1]

Getting too rich on these warm days so have dropped main to 132 - same as stock. I think I'll keep it like this when it gets colder as it is still a little rich.

Connected up my fan at last .

[knackeredMk1]

Adapted some new CR/CRF wheels to fit (Talon hubs/Morad rims/Battlax BT92 (120/70 & 150/60)).

Needed to make new spacers and get a special rear disk made by EBC. Also needed to make spacers to bring the rear and front sprockets out very slightly and use a standard chain (rather than O or X ring) to avoid the chain catching the tyre that you almost always see with SM conversions. Whole bike is 2 inches lower and now feels like a toy

[knackeredMk1]

Just fitted new X2 headlight (Halogen not HID ). It is a really tight fit so I had to remove all excess wiring, replaced some connectors, changed ignition switch (£2.99) and changed capacitor (Thanks to KWM_gbr ).

Has much better road legal dip and main beam. I have also wired up an 'all on' from the standard Honda light switch.

[knackeredMk1]

Changeing the look of the Mk1 a little also fitting a Stan Stephens tuned barrel, a Mugen head and the wider gearbox of a Mk2.

New look powervalve cover. Filed flat, powdercoated, mugen sticker and six coats of varnish.

[knackeredMk1]

Removed stickers to get closer to the original look. (Bit grubby at the moment ).

[knackeredMk1]

Those who are familiar with this project will know that I have a Mk2 barrel and AR head on the basic Mk1 engine. This in itself gives on paper a little more power than the standard Mk1 barrel which is a bit messy in the powervalve area.

This is a bit of a shortened version but gives the basics of what happened over two weeks at the college workshops. -

I chose as a bit of a project for this year, to rebuild the engine with a fully bored out barrel and a Stan Stephens tune on a Mk3 cylinder. I also planned on swapping the gear cogs for those of a Mk2 so as to make the gears slightly wider and raise 6th by 7%.

In the end I didn't split the crank case as I found the engine responded to setting the powervalve to the point where it was trully fully open when the powervalve servo is fully open, rather than the Manual settings. This is because the raising of the exhaust port in tuning means that the PV needs to have a slightly anti-clockwise starting position to enable it to match the port when fully open.

I did however get a Mk3 barrel bored to 68mm and enduro tuned by Stan Stephens. I will write about the tuning later.

I fitted the new barrel, a new Wiseco piston and a new Mugen head. The Mugen head was to raise the compression ratio. In fact it raises the standard AR CRM from 6.7 to 8.0.

I warmed the engine up and went for a short run. Very short as it only lasted about 600m . The engine started 'pinking' from pre-ignition so I stopped it.

When I took it apart I found many very small vertical ridges all over the exhaust port side of the inside of the barrel. To cut a long story short we found that the piston rings didn't have the required end gap when inserted into the barrel and had to be filed down a little to allow the specified clearance. What had happened is that the rings had expanded but there was no room at the ends so they had cut into the sides and made the scoring.

I then rehoned the barrel, which got rid of the very small marks, and refitted the piston etc. There was no damage to the piston itself. But this time I left out the Mugen head to be sure.

I've changed the jetting by dropping the main to 132 and lowered the needle by one slot. What I've ended up with is more mid range and top end power but below 3,500 rpm the engine is a bit rough on very small throttle openings. As a road engine it is very good but I'm not so sure about trail riding in Winter.

This roughness disappeared after fitting the Boyesen Rad Valve. So was jetting related.

[knackeredMk1]

Fittted XR400 forks. They give only 11.0 inches of travel compared to 12.2 from the CR125 forks but they are the same length top - spindle as the original Mk1 CRM forks. They have adjustable rebound damping with less overhang. They are much more tunable and there are springs available. I have fitted 4.5kg springs and softened the compression damping. I have put 5wt oil in. Saves a bit of unsprung weight as well.




I have also fitted a Boyesen Rad Valve which should give a little power increase across the range.



The reeds for the Rad Valve are the racing version of the Dual Stage reeds -