There have been a few questions regarding piston replacement on the 4RT.

For info my mate has just stripped his motor that was delivered in April 05 and trialled all seasons from then,

we estimate approx trials 500 hrs. This piston measured 76.440mm which is 0.050mm above the specified service limit.

Or about half worn. Air cleaner has always been kept cleaned and oiled but otherwise no special maintenance.

Hey, now that is impressive!

What engine oil has been used and how often has it been changed?

Didi it get a new oil filter every oil change?

Thanks, Ralphy

Wow, that's impressive.

How many times did the valves have to be adjusted?

Hey, now that is impressive!

What engine oil has been used and how often has it been changed?

Didi it get a new oil filter every oil change?

Thanks, Ralphy

Wasn't met to impress just put some numbers behind the speculation that I see on the site.

I had the bike for the first year and ran Pro Honda HP4 10-40.

Since then it has been run on Mobil 1 synthetic and changed along with filter every four or six trials.

Valve clearance he checks twice a year.

I was amazed at the condition of the motor considering the work it has done, there was some light pitting on the exhaust valves but that was all.

We don't have any trials here with high speed road sections involved but do have a number of properties that have laps of 5-6 km and a Scott type event where the laps are around 45mins each and of course often hot and dusty.

With valve clearances I am ashamed to admit that after finding nothing changed with my first bike I didn't get round to checking my Repsol valves until I had done 53 events and logged 200 hrs. The bike had been getting hard to start when hot, needing 3-4 kicks when left at a section, when I checked valves the exhaust had closed up to 0.18mm. Resetting to the specified 0.30mm instantly cured the reluctance to start.

I may just jinx them now ,but i dont thunk i have heard of any engine problems with the 4 rt

sounds promising though,i have checked my valves a couple of times and they have never needed any adjustment (06 model)

I remember the pundits saying that the 4RT would require a new piston every 20 hours

I remember the pundits saying that the 4RT would require a new piston every 20 hours

Which pundits where?

I,ve had my 4rt nearly 2 years now and bought it second hand as a year old bike. I've changed the oil filter twice,engine oil 4 times and clutch oil twice although once would have done. I estimate I,ve ridden it 7-800 hours so far not including the Scottish and Scott the previous owner rode. It has never let me down, it rides exactly as it did the day I bought it and always starts first kick from cold. Yes shes a heavy old bird but I would'nt swap it for any bike yet, they are amazing

Gday, the engines are relatively unstressed in the 4RT compared to their "brothers" in the CRF. I have rebuilt quite a few of those... Regular Oil changes and other maintenance seems to be a key factor, just like with any bike. It will definately pay to check and measure the gudgeon pin as that is a weak area in that motor. I think the CRF's were meant to be replaced every 15 hours or so in the earlier bikes but this would be overkill on a trials bike as the revs are nowhere near as high and sustained.

Cheers,

Stork

Edited August 19, 200917 yr by Stork955

Gday, the engines are relatively unstressed in the 4RT compared to their "brothers" in the CRF. I have rebuilt quite a few of those... Regular Oil changes and other maintenance seems to be a key factor, just like with any bike. It will definately pay to check and measure the gudgeon pin as that is a weak area in that motor. I think the CRF's were meant to be replaced every 15 hours or so in the earlier bikes but this would be overkill on a trials bike as the revs are nowhere near as high and sustained.

Cheers,

Stork

also the MX motors eat vaves,it seems to be totally on hours run and not how hard they are used ,but as youy say the trials derivative is under stressed .

There have been a few questions regarding piston replacement on the 4RT.

For info my mate has just stripped his motor that was delivered in April 05 and trialled all seasons from then,

we estimate approx trials 500 hrs. This piston measured 76.440mm which is 0.050mm above the specified service limit.

Or about half worn. Air cleaner has always been kept cleaned and oiled but otherwise no special maintenance.

You bike's not run in yet, it needs a load more hours. I think JR Sunt needs to post about how long a 4RT needs before rebuild. His bike has had more tap than any I know & I mean serious tap.

yep they do were, price one up a barrel & piston u will be suprized how cheap they are from the main inporters

You bike's not run in yet, it needs a load more hours. I think JR Sunt needs to post about how long a 4RT needs before rebuild. His bike has had more tap than any I know & I mean serious tap.

Well our David's '07 4RT did the SSDT with you riding it in 2008, then he did the SSDT on it himself, sold the bike to one of the observers and the motor still hasn't been apart! no reason to be taken apart either!

As you say J Sunt did a few SSDT's on his '05 bike before he rebuilt the motor and had ridden everything else in between!

Big John

yes john, a cracking bike. carefully run in and set up by its first owner .

yes john, a cracking bike. carefully run in and set up by its first owner .

Absolutely right Munch, that 4RT motor was (and still is) as sweet as a nut!!!

Big John