Dirty ugly 4RT rebuild.

[ahell]

 

I bought this Montesa 4rt in June. I've been meaning to post the work for a while.

A touring motorcycle...
It's rotten, completely neglected... but I got it for an indecent price. (and I have quite a few parts)
There it is, disgusting at its purchase.

 

First step washing the machine ...

Iin the trash:
The swingarm, the chain kit, the tires, the trim, the air box, screws, pads, rear disc, etc.

I repaired the chassis, the bearings, sandblasted the triple clamps, fitted a tech aluminum fork, new braktec master cylinders, new latest generation braktec caliper and new hose. 

The orange wheels were in good condition but I didn't want to restore it in Repsol.
By stripping the orange paint, I discovered a superb gold. (Standard 4rt has gold wheels)

 

 

I still have some paint and primer left to remove from the wheels before replacing the tires.

I repainted the ignition cover, did the service... and then there was tragedy.

 

Very low oil level on the engine side, lack of lubrication, timing chain shoes which are melting and sticking in the suction strainer.
Basically, I have to open the engine.
I don't know what I'll find, even if it doesn't click.
But I'm going for the skates, the timing chain, the bearings at a minimum (there is some play).
While knowing that there are great misfortunes that the piston, the connecting rod, the cylinder... in short we will see.

 

 

 

I'm going to take inspiration from a full black motorcycle that Mitani had prepared. I might reassemble an original Showa in tees repainted black. As for the wheels, we'll see. I still have a set of 315R wheels that I can repaint black...or just keep the gold ones. I received a Rikizoh adhesive kit from Japan black RTL, black mudguards and had purchased a flat tank for a while.

[RonH]

I gotta say that I love your posts and seeing “rotten” turned to “gold”. Can’t wait to see the end of this show! Thank you!

Edited November 2, 2024 by RonH
Typo

[exman]

I can't tell about machine, but everything else I'd restore whispering.

[ahell]

After more than a year,
It's time to work on this bike!

Meanwhile, the motorcycle was assembled and stored with Morad wheels in poor condition and a Showa fork.
The shock absorber needed servicing, etc.

So,

I installed a machined top triple clamp from the HRC Repsol kit.
New Tech gold forks, fresh DID wheels, new Galfer discs, new S3 black handlebars,
all new Braktec front brake and clutch, carbon fork guards and swingarm.
And a restored Showa absorber with stiffer grey spring.

The entire chassis is new or overhauled.

To do:
Some titanium bolts and welding on my Future flat tank.

The engine still needs to be opened up.

Edited May 5 by ahell

[RonH]

I forgot about this bike and it’s great to see the progress. The black scheme is awesome!

[ahell]

Some titanium bolts

[ahell]

It's time to see what's going on this engine.

Cameshaft and bearings perfect

Cylinder rock solid! Perfect !

Piston very worn but nicely worn 😅

The crankshaft need new bearings

New timing chain and new white guide needed.

Good news.

And because it's a 250 cc, parts are less expensive than 260 / 300 / 301 !

Edited yesterday at 10:02 AM by ahell

[ahell]

A new conrod is coming.

To much gap for the piston axle.

[ahell]

Here's my assessment of this engine.

It's not pretty.
Low engine oil (in the engine compartment, not the gearbox, I should clarify, because it's separate on this model).
The white timing chain guide is starting to melt in small pieces (which end up in the oil strainer).
Engine overheating... blown head gasket... no coolant... burnt oil getting into the cooling system... fantastic!

Well,
This engine is built like a tank!

There is some wear, but frankly, it's very surprising how little there is.
The crankshaft bearings have some play, but they don't make any noise.
The connecting rod big end has no play at all... but the small end shows significant wear without any material being torn away.
The piston pin is still within tolerances. No discoloration from overheating or any apparent defects.
The piston is out of order, but without any signs of seizing.
The cylinder is good. A quick hone for the occasion, but nothing more. (phew, €€€)
The cylinder head needs checking. I have a broken screw in a thread that's causing me a problem.
Another used cylinder head is arriving, and I'll take the opportunity to rework the ports because there are some significant steps.
Valve stem seals will be replaced, and the valve seats will be checked.

The rocker arms are good, the camshaft is perfect, as are its bearings.

Considering the conditions this engine has run in,

it's a miracle it's not destroyed.

The reason?

It's an engine derived from a motocross engine, so it's oversized for trials use in many respects.

I'm going to rebuild it properly with a new cylinder head, connecting rod, piston, bearings, and gaskets, and that will be a great chapter in this motorcycle's history!