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Montesa 4 Ride Oil Filtration Issues


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I bought a brand new 4 Ride in April last.  Ran it in for 260 miles before servicing it prior to a weekend trail riding in N Wales. The oil filter was bone dry with a dribble of oil sitting inside the filter housing. Aaaargh!

Fortunately I still had my old CRF for the weekend and the 4 Ride went into the dealer a couple of days later.  They said that there was no issue that they could find as they replaced the filter, ran the bike and opened it up again to find oil as they would expect to see.

Vaguely reassured, I took it to France for three days trail riding and then to Devon in December, nearly 400 miles.  Took it apart for an oil service and found a dry filter again!  Even the grease on the filter to hold the spring in place was still there.

Having broken my front mudguard in France I was sourcing a replacement and found myself talking to Gordon at Mickey Oates in Glasgow.  He was very helpful and forthcoming so I told him about the oil issue.  He told me that they had seen this problem before due to a blocked/ incomplete oil way in the crankcase cover and that Honda had replaced them.  He kindly offered to send me photos he had to help identify the correct holes to pour oil into and check that it flowed through.  Well, Xmas was upon us and I am only now getting around to checking it out.

Unfortunately I did not get the photos because Mickey Oates closed it's doors for good not long after I called (sorry guys) and are now not available to help.

Looking at the exploded parts diagrams and the actual crankcase I am assuming the duff oil way would be in the area of the pressure relief valve, which looks to be after the oil filter in terms of the flow direction.  There is no obvious exit point for oil anywhere near the PRV so maybe this is the problem?

I cannot ascertain if the oil system is a 'total flow' or 'bypass' one.  Therefore, can anybody help with the following before I go out to bat against Honda:

1. Anyone else experienced this?

2. Is the system total flow or bypass?

3. Even if the system is a bypass one, no filtration will have been taking place.  How concerned do I need to be about damage/wear up to this point?

Any feedback appreciated :(

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Some thoughts:

1. 260 miles before the first oil/filter change is a long time.  Reviewing my old 4RT manual says the break-in period is 20 minutes.  After which it implies the oil and filter should be changed.  (Personally, I'll probably go more like an hour lacking any other guidance.)

2. Seems to me it was possible to install the oil filter backwards in that engine (and thus blocking all flow).

3. What transpired between the time the dealer said there was oil in the filter and you subsequently observing there was none?

4. Small 4T motorcycle engines sometime have no oil filter, so it's not the end of the world, but far from ideal.

5. The engine would have seized long ago with zero oil flowing.

6. I assume the oil looks used and oxidized, rather than like new (which would indicate it had not flowed anywhere).

7. I also assume that if you remove the tappet covers you will see oil.

8. If you are concerned about engine damage, you should submit a sample of the drain oil for analysis.  In the US, I've used Blackstone Labs: https://www.blackstone-labs.com/tests/standard-analysis/   They can determine the presence of wear metals in the oil.  I'm sure there are similar labs in the UK. 

Edited by konrad
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Hello Konrad, thanks for responding.

First service is due at 500 Km (312 m) and subsequently at 1000 Km intervals, so I was ahead of it a little at 259 m.  The filter would be difficult, if not impossible, to fit the wrong way round, so no issue there.

I covered around 400 miles after the dealer said no problems.  I would expect the filter element to be swollen and discoloured after this, which it was not. Also, the outflow/exit from the filter chamber is an orifice in the centre of the sealed filter retaining plate, so it cannot drain down over time.  Therefore, on removal the chamber should be a bit less than half full, yet there was just a dribble lying in the bottom. Probably what the dealer saw and took to be adequate, if indeed they ever did look?

Clearly oil is circulating around the motor, otherwise it would have gone terminal by now, as you rightly point out.

The more I think about it, I am pretty sure it is a bypass system as any exit that is, or should be, in the crankcase cover can only deposit oil back into the main chamber and sump. I don't know what the design proportion of oil to go through the filter is (10% ?), but there has been no filtering at all up to this point in time. Probably not the end of the world, as you say.

However, I think my next move is to remove and check the PRV which should be controlling the oil flow rate.  Maybe it is defective?

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I am fascinated by these sorts of problems.  But I'll start by saying the only motorcycle oiling system I've studied in any detail was for a dry-sump Aprilia vee-twin which was  more complicated.  So the following is conjecture.

The block flow diagram below is for a 1977 Kawasaki KZ650.  It represents my understating of the pressure relieve valve's place in the system.  Its purpose is to prevent oil pressure from exceeding a preset limit.

The bypass valve opens when the oil filter is clogged or when the oil is too thick (e.g. cold weather startup).  The bypass valve can be external to the oil filter or internal.  I would expect the 4RT to get 100% filtered oil under normal operating conditions.

I suggest opening an old oil filter to have a look inside.  If an internal bypass is present, there should be a spring and some type of valve.

But if the bypass valve is external, and stuck open, I could see where your engine could still be running okay yet have no oil in its filter.

kz650 oil flow.JPG

Edited by konrad
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Like you say, there must be oil circulating in there or it would have expired. I’ve had two experiences and one resulted in a new bottom end due to oil starvation. After damaging the generator cover on a rock the little pencil like raised bit that runs from the filter back into the centre of the crankshaft which is the oil way, I had the cover welded and it blocked the oil way, the con rod was shot in no time. 
A friend who also had a 4rt thought he had changed his gearbox oil but had drained the engine oil and filled it with gear oil, the bike ran fine pottering around but as soon as you started to push it hard it just wanted to bog down - I presume the gear oil was breaking down under pressure and heat. 
It is not uncommon for the grease to be on the filter spring and the difference in millilitres between an oil change and an oil and filter change is only 30ml, the filter should have a coating of oil on it but it’s now swimming in it. You may be able to blow down the oil way in the generator cover to see if it frees, I’ve never tried it so it may or may not be open. 

Hope this helps. 

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Hi jrsunt,

Your post implies that the flywheel axle has an oil way leading to or from the crank big end housing? Do you know which way the oil flows?

Also, I would think that the oil filter chamber should be full of flowing hot oil during operation and any grease on the spring would be quickly dissolved into the main oil volume?

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In all engines, oil flows towards the big-end bearing.  When it escapes the big-end bearing, it returns to the sump.

P.S. From my research, oil filters almost always flow from the outside to the inside. 

P.P.S. It seems that canister-type filters are the ones that have an internal bypass valve.  So I'm guessing you won't find a bypass valve inside the 4RT's paper cartridge.

Edited by konrad
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As Konrad says, in theory it travels from filter to crank. If that wasn’t flowing your engine would be dead. 

After your dealer visit and 400miles covered, did you drain the oil? Was it discoloured? Was the filter still looking yellow and brand new even though the oil was looking used? 

It is very common on 1st service 4rt”s to have the original Honda grease on the spring, but the filter and oil would be very discoloured. I’ve done quite a lot of them. 

I think I have an old generator cover that’s been stripped, If I do I’ll have an investigate. 

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That's what I have always understood, which is why I am confused by the oil coming from the main crankcase orifice into the filter chamber and then out into the crankcase casing via the filter retaining cover.  If it is a full flow system then that filtered oil should be making it's way to the big end et al somehow.

Now it occurs to me that an oilway in the cover takes the oil to the roller bearing and oil seal in the crankcase cover allowing pressurised oil through the crankshaft to the mains and big end?  That would be very worrying as it would mean no oil making it's way to where it is needed etc.. Though if that were the case they would have gone by now!

I am going to have a better nose around tomorrow.


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Hi jrsunt.

The first service I did the filter was bright yellow and dry and the oil was discoloured. The dealer put in a new filter (but a hi-flo by the look of it) and said they changed the oil too before running and opening it up again to check. 
After Devon the oil was pretty dark but the filter (brown paper with wire mesh) was dry and leaving it on a piece of tissue for 20 minutes left no sign. There was a dribble of oil in the bottom of the filter chamber which was clearly cleaner than what came out of the sump. 
See my last post to Konrad regarding my thoughts on the crank oil feed. Is that right, do you know?

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Just so we are on the same page, I grabbed some images from the 2018 4RT manual.  Here is what I think is going on:

1. Oil comes from the pressure pump and surrounds the outside of the oil filter.

2. Oil travels through the filter media and exits via the center of the filter. 

3. Oil exits the filter cover and enters the generator cover.

4. Adjacent to the oil entrance in the generator cover is the PRV (excess oil pressure is vented to inside of the generator cover, eventually finding its way back to the sump.)

5. Oil travels through a passage cast/drilled into the generator cover towards the crankshaft big end.

6. Now I'm guessing... Some of the oil passes through the crankshaft and continues on to lube the piston and top end. (Or there's a different passage in the generator cover that directs oil on to those other locations.)

4rt oiling 1.jpg

4rt oiling 2.jpg

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It does sound a little worrying as the filter is not receiving oil and then not delivering oil to the big end. As far as I know there isn’t a way to test the oil pump. To get to it is an engine out and split job. There is also a reed valve type device before the pump. You could perhaps take the valve covers off and see if oil is getting to the top end whilst it is running, not a quick job on a 4ride though. 
 I’d be trying to get it looked at under warranty, Honda aren’t that bad to deal with if you can get to speak to the right person, an example, of a engine I rebuilt whist at a Honda dealer, a 4ride had been drowned in a river, needed full bottom and top end rebuild managed to get all parts covered on warranty and just paid labour. You’re in a slightly better position as you haven’t fcked up and it sounds like a manufacturing defect. Honda generally want pictures of everything (genuine filter would need fitting) and it gets up loaded onto their dealer network. It’s a pain in the a*** to do but would be worth looking into and it’s not in the Honda mindset to have engines failing. Where did the bike come from?

Edited by jrsunt
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If the Oil Strainer Screen is plugged the pump and filter will starve.  I didn't see mention of the strainer screen outside of the Engine Oil Flow Chart pictured above.  

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