Knackered's Project - Highly Modded Mk1

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Knackered's Project - Highly Modded Mk1

Post by knackeredMk1 » 03 Jan 2008, 20:23

In order to take advantage of the new photo viewing format and tidy up the post I am starting this final evolution of 'Knackered's Project'. There are a lot of discussions, abuse :wink: , errors, supporting posts and 'blind alleys' that have been removed from the original so that this can be read in a straight chronological sequence.

I bought a wreck of a Mk1 in November 2006 and have done it up over almost 2 years. In its history it has been well looked after at stages and completely abused at others. One of the previous caring owners was Purple Rooster of this board.

The plan was to bring the bike back to full health whilst trying to improve on the original; but not stray too far by making it into a road going MXer, for example. I want to keep the ease of use, road going comfort, smoothness and torqueyness of the original.

To begin with I stripped the bike down so as to know what needed repair and replacement. Unfortunately it was all worse than I had anticipated.

The only things that are going to be the same when I finish are (as of 01/06/08):
Rear axle
Powervalve servo
Louvres in front of the radiators
Powervalve control module
CDI

Everything else will be repaired or replaced because the original is knackered and/or I want to 'improve' on it. ('Improve' is in the eye of the owner, not necessarily anyone else. :wink: )

The frame almost unchanged from being stripped down (Have ground a few bits off & replaced twisted subframe):

Image

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Forks

Post by knackeredMk1 » 03 Jan 2008, 20:26

The original forks are 41mm diameter with very little damping, soggy springing and pitted chrome. I had a set of CR125 1989 forks reconditioned and powder coated to replace the originals. I had to have the yokes machined out to fit the 43mm diameter.

The new forks are much better damped, have compression damping adjustment and slightly heavier springs. They are a bit longer in the stroke but the original geometry of the bike can be kept by raising the forks slightly in the yokes. I'm also going to raise the rear slightly to match the longer travel of the later models and change the shock.

Fork comparison:

Image

Later Post Script - Probably the best option to replace the forks are the last itteration of the XR250. You won't need to enlarge the clamps and you will get better springing and cartridge damping. XR 250 forks are a direct replacement and are the same length as the Mk1 originals. Otherwise XR 400 forks are good but you will have to mill out the clamps. They are slightly longer so to keep the geometry you will have to mount them lower through the clamps.

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Rear Shock

Post by knackeredMk1 » 03 Jan 2008, 20:31

The rear shock is completely shot. Not suprising as the bike is 19 years old. When I had a Mk1 way back I replaced the shock with an Ohlins unit. I had a quote for doing the same again (£500) but this was too expensive.

I found that a Mk2/3/AR swinging arm and linkage fitted the Mk1 frame. All I needed to do was figure out a way of connecting the top of a newer model shock to the frame. I discovered that this was all but impossible for a Mk3/AR shock but was doable for a Mk2.

Original:

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Cut and drilled:

Image

Finally welded (agriculturally!):

Image
Image

I managed to find a new Mk2 shock from Crasher76 who also frequents this site. I'm not sure of the origins of this as it is made by Kayaba and the OEM was Showa. It also has rebound damping adjustment and a much larger reservoir than OEM Mk2. Mk1 shocks are not rebuildable but all other Mks are. (Have since found that Mk1 shocks are rebuildable. Also the replacement shock was originally meant for an XR250R that just happens to have the right characteristics. (Hagon make the same shocks for the Mk2 and the XR250R))
Shock comparison (Mk1, Mk2) :

Image

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Rear Brake System

Post by knackeredMk1 » 03 Jan 2008, 20:37

The original rear brake was knackered. I wanted to replace it and remove the messy original brake light switch system. I have fitted a CRF master cylinder and removed the original remote reservior. I have a pressure switch on the top of the master cylinder to activate the brake light rather than the unreliable original.

I could probably have got away with a straight replacement of the original master cylinder with the CRF one. However I wanted to replace the brake pedal with a CR500 one which has a longer arm that connects with the master cylinder. This meant that I had to cut the mounting bracket to relocate the top mount. I have replaced the seized brake caliper with one from an XR400.

Image

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Airbox and Intake to Carb

Post by knackeredMk1 » 03 Jan 2008, 20:46

In a bid to get the Mk1 to take more air and thus produce a tiny bit more power, I got a different air filter frame. The new one is an XR400 'powerflow' frame from Twinair (plastic).

Image

I also wanted to improve the air flow through the airbox. I cut two 2.5cm diameter holes in the top of the airbox and inserted somes carbon fibre tubes.


Inside:

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From the top:

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I'm not sure of the exact function of the 'boost bottle' that is attached to the boot that takes the air from the airbox to the carb. From the information I can gean there is one faction that says they are useless and one faction that says they give a small benefit to low end power but only when the 'air intake system' contains a certain volume of air relative to the capacity of the engine.

Seeing as I would have to soften the plastic of this 'bottle' and change its volume to allow for the tank change I'm going to make, I thought I might as well get rid of it and replace with a Mk2 boot. The Honda CRM250R factbook says it is 'better than the Mk1'.

01/03/08 - I now believe this is some kind of resonance chamber designed to improve throttle response at low/medium revs.

Comparative photo:

Image

Some debate and research concluded and I replaced the Mk1 setup with a Mk2.

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Footpegs

Post by knackeredMk1 » 03 Jan 2008, 20:58

Old v New (XR650R Stainless steel):

Image

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Tank

Post by knackeredMk1 » 03 Jan 2008, 21:09

The original tank was actually fine but I wanted to replace it with a thinner tank to be able to get further forward when cornering (CRM bugbare). The new tank is also 1.5 kg lighter.

The tank I am going to use is from CR125 1989. Side by side comparison:

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The fit of the tank allows the front part of the saddle to be a more gradual slope:

Image

I had to weld on a fixing point as the original was on the main frame:

Image

I intended to polish out all the marks and scratches of the new tank but after ~ 4 hours I gave up and put on a modified set of CR500 stickers:

Image

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Seat

Post by knackeredMk1 » 03 Jan 2008, 21:32

The foam on original seat was shot. I physically compared most CR/XR seat foams with the original and none matched. The closest to Mk1/Mk2 is 1989 CR500 (Mk1) but this is shorter, narrower and slightly taller.

I wanted a seat that was lower at the back, narrower, slightly taller than original and flatter across the middle so I went about making my own. 3 original seat bases, one new CR500 1989 foam and one new CR500 seat cover later and I cut too much foam off. I finally realised that I wasn't going to make a hybrid seat that fitted.

I took a gamble on a nearly new CR500 (Mk2) 1995 seat from the US on eBay that came off. Below is close to how I think the new setup will look. I won't make the final fixings until I've got at least a rolling chassis.

Image

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Rear Mudguard/Number Plate Holder

Post by knackeredMk1 » 03 Jan 2008, 21:42

Have fitted new no. plate holder to rear fender. UFO item LEDs tail light/brake light. The fender is for CR 1989. It is exactly the same as CRM but without the cutout for the original rear light.

Image

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Engine Disassembly Tools

Post by knackeredMk1 » 03 Jan 2008, 21:49

Have just finished stripping two engines. I thought I would list some tools that I've found useful.

Clutch holder made from plain clutch plate and 12x4mm steel.

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Balancer shaft needle bearing remover. Total length =100mm. Smaller diameter = 25mm long.

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Crankcase seperator. Plate that goes on the LH crankcase. The outside holes are drilled to take M6 bolts through to the case and the middle hole is for an M12 bolt to pull the plate away from the input shaft. The M12 bolt has a concave end and a suitable steel ball bearing is between it and the shaft. The plate is 12mm aluminium.

Image

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Stainless Steel Brake Lines

Post by knackeredMk1 » 03 Jan 2008, 21:54

Have a set of new stainless steel brake hoses from HEL. (Andy as hel_performance on eBay).

Took a little time as front is special order but excellent customer service.

Should provide a lot more feel and power :D

Image

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Clutch Basket

Post by knackeredMk1 » 03 Jan 2008, 21:56

Have split two Mk1 engines recently and found them to be in generally excellent condition. The one fault in common is wear to the clutch basket.

The picture below illustates this and shows how the clutch plates have indented the sections on the basket. This causes - harder to pull clutch, needs lever to travel further, dragging and slipping.

It occurred to me that this might be the cause of some clutch related problems on this site?

The remedies are - New clutch basket (£340 Honda 30/03/08) or file the grooves flat. Filing the grooves is a cheap and easy solution but in the medium term the grooves will come back more easily than before.

Image

I filed one basket - Very fine file first followed by 1200 wet and dry stretched over file. I tried to take as little as possible off.

Image

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Clutch Basket

Post by knackeredMk1 » 03 Jan 2008, 22:07

I tried to find a way to buy a new aftermaket clutch basket. But None of the CR/XR fit. The CR 125 & 250/500 are close in construction. The CRM uses 10 tabs on the clutch plates and so does the CR125 but the basket itself is different. The CR250/500 has the same type of construction as the CRM but has 12 tabs on the clutch plates. It might be possible to replace a CRM clutch with an entire CR250/500 unit though.

As a project I chose to make a new clutch basket out of an aluminium block with lathe and mill.

First day:

Image

Third day:

Image

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Sidestand

Post by knackeredMk1 » 03 Jan 2008, 22:10

Have a choice:

Image

One weighs 560g one weighs 185g!

In the end I went back to an original CRM sidestand as the aluminium one was not strong enough (Mk3 as longer than Mk1 so suited this project).

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Radiators

Post by knackeredMk1 » 03 Jan 2008, 22:13

Gently shotblasted the radiators then gloss radiator paint - probably should have gone for satin but they're OK.

Image


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