Hello

 

My 301rr has a knocking noise on low revs. Not sure what it could be but a good mechanic told me it sounds like a worn piston. Bike is a 2020 and it has been used most weekends. Bike has no vibrations and runs great, it doesnt smoke. 

Anybody had to change their piston on the 301? Could their be other issues with the bike? Main bearings, big end? Or is this not something that goes wrong quickly?

 

Kind regards bob

Before going all in on that I would double check the timing chain tensioner.  I know that you can get a noise that sounds a bit like piston slap from the chain.  Would be the least invasive check and if the issue would be one of the lower cost options.  Well worth a look in my opinion. 

Also, unless you put piles of hours on your bike or are not doing oil changes it is more likely something simple like the tensioner than a piston issue considering the year of even the oldest 301's in comparison to how long most Montesa's last in my opinion.  good luck. 

Edited January 29, 20242 yr by jonnyc21

Too new to expect serious problems, I would check the plug gap or replace the plug, check the air filter for cleanliness and the correct saturation of filter oil, basically anything that would cause fuel to incompletely ignite in the combustion chamber such as the ignition timing.  

As mentioned before, I very much doubt it will need a piston or cam chain unless oil changes have been seriously neglected, they are properly built.

 The cam chain tensioner is self adjusting and shouldn’t be out of spec at that age, but well worth a look. Checking valve clearances would be an easy one too. 

3 hours ago, jrsunt said:

As mentioned before, I very much doubt it will need a piston or cam chain unless oil changes have been seriously neglected, they are properly built.

 The cam chain tensioner is self adjusting and shouldn’t be out of spec at that age, but well worth a look. Checking valve clearances would be an easy one too. 

I only suggest the cam chain tensioner because I have heard of a few of them having issues where they would bind up and not keep the needed pressure and so get some chain slap.  Where not a common issue one of the ones I know about was on a newer 260 (couple years old) so figured considering how easy it is to check that part it was worth a look. 

The one I indicated here was replaced by a manual tensioner and the sound went away and the owner likes it better, however if swapped with a manual version it would need to have the tension checked from time to time. 

What ever the case I hope it turns out something simple to fix it like changing fuel, the tensioner, or spark plug etc. 

 

Check that your oil delivery hole is not plugged, possibly even since new, somebody just now reported that issue on a 4-ride, & that would certainly account for an engine knock.

On 2/6/2024 at 6:30 PM, lemur said:

Check that your oil delivery hole is not plugged, possibly even since new, somebody just now reported that issue on a 4-ride, & that would certainly account for an engine knock.

 

@bobb so what's the diagnosis, Is she going to live or require surgery? 

well she is still running ok 

i put thicker oil in it 10w60 motul and a lot less noise 

a lot of people told me 10w30 is to thin ( that is what honda has in the manual) and causes the bike to run noisy

the importer here also told me he never uses 10w30 

i guess the oil delivery hole is fine? bike would have been knackerd now if it wasn't?

 

1 hour ago, bobb said:

well she is still running ok 

i put thicker oil in it 10w60 motul and a lot less noise 

a lot of people told me 10w30 is to thin ( that is what honda has in the manual) and causes the bike to run noisy

the importer here also told me he never uses 10w30 

i guess the oil delivery hole is fine? bike would have been knackerd now if it wasn't?

 

The person that reported the oil hole problem said the symptom included oil never making it to the filter.  If your filters get dirty we can assume that is not a problem.

All I ever used was Repsol 10w30 as per the manual, it only holds half a litre so I changed it lots.  Never had piston problems even after dropping one in the lake.

oil gets to the filter so that is no problem.

I have been told by a mate who had 2 '4 rt's his first one was very quit and the second one was noisy from the start. Enine got checked over and there was no issue and his bike ran perfect for over 5 years. Maybe some engines  are just a bit more noisy ?

 

Hey,

 

I finally opened the 301 engine and my friend the mechanic was right piston was worn quite badly.

No big damage to te cylinder wall just needs a light hone and an new piston and rings. Will fit a new distribution kit too now the engine is in bits.

Bike has been well serviced and i use good full sysntethic oil. Maybe previous owner didnt serviced it enough? 

some pictures of the damage

You sure you want to hone a plated barrel 🤔 don't think you are suppose to do that.

that might be correct! 

parts are at the mechanic i tought it was a steel liner inside the cylinder but i only have seen the pictures