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XR600R what causes so many fried heads/cams?


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Checking these forums and flea bay etc I see a load of Xr600R with fried heads/cams/busted pistons.

I don't want to follow that path!

So is this an achilles heel and is there a cure?

Assuming you do all the usual 'health and hygiene' like oil changes, valve adjustment - y'know, the stuff...and you don't have a weak or knackered oil pump....is there anything else?

I did read of someone opening out the oil line feeding the head but also think this may be counter productive as it might it reduce pressure too.

TDD

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It's a good question.

People blame the oil pump, but I feel the issue is really the oil supply to the oil pump. First is running out of oil, second is the frame tube oil screen getting overly clogged, fourth is twisting of the oil supply line.

Just plain overheating is another cause I am sure.

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There have been discussions here and here about the RFVC oiling system before and there are a lot of potential factors involved with a top end or piston failure. Guaranteed ways to scatter an engine are to overheat it or run out of oil and both are done surprisingly often. A guy on ADV just burned up his XR600 while in Mexico and I strongly suspect that it was caused by those two factors, among other things. There is another guy on ADV that has gone just about around the world on his 650L with no problems.

I did read of someone opening out the oil line feeding the head but also think this may be counter productive as it might it reduce pressure too.

There really isn't any measurable pressure, at least not when the engine is up to operating temperature.

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Hondas XRs use a low pressure/high volume philosophy. Every hi speed bearing in the motor is an anti friction type except the center of the cam. If oil gets low, lubrication AND cooling are compromised. Low oil will overheat them and then the oil film strength will fail. Virtually every head failure can be traced back to this at some time in the lifespan of the engine. Once damage is started it can't be healed, it just gets worse.

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Nice - three informative responses, thanks guys.

After a few very hot desert trips without incident - but noting my vapour head/oil line sensor was indicating the kind of temps that cause oil to begin to break down - like above the 250F mark - I went ahead and fitted an oil cooler and did the big fin mod just to be super sure I was doing everything possible to keep temps down.

So far so good - but looking at that weedy little oil line to the head has me wondering if it could use more flow...not informed enough to make a call on that...could I potentially stuff it up if I installed a wider pipe and opened out the banjo bolt holes a bit??

few pics of the cooler and my making up the big fins and finished job.

IMGP1409.jpg

P1290036-1.jpg

P3160173.jpg

P3160180.jpg

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So far so good - but looking at that weedy little oil line to the head has me wondering if it could use more flow...not informed enough to make a call on that...could I potentially stuff it up if I installed a wider pipe and opened out the banjo bolt holes a bit??

A few others have done that, but I'm not sure of the long term affects at this point. The crankshaft is also fed by the same pump as the head, but I'm not sure what the cranks needs as far as minimum flow. Roller bearings typically don't need much oil volume, but the oil is responsible for a lot of cooling in these engines.

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the main area in the cam is not touching the head, i looked at it real good and there is no contact.

i think that when running without oil the cam temp rise up what lead it to expend and then to touch the head and making a mass.

i also think that the banjo hole ratio should be the same, Honda didn't put different hole size there by mistake.

there is a speed/presser that should be in the oil line and in the head cover.

the main problem i think is the heat in the head, so try to taking it down will make thing better.

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My take is that most of the top end failures are due to excessive heat, broken down oil, insufficient top end oiling due to a restricted inlet/return hose screen or a combination of any or all the above. Twisting the return line when reinstalling the oil screen can also be a problem. Pay attention to these potential problems, use a high quality motorcycle specific oil and don't get the darn thing too hot. Jetting slightly on the rich side can help keep things cooler. Using a thick oil in cold weather can cut down oil flow to the top end on cold starts. If you suspect that oil flow to the top end is insufficient, crack open the oil line banjo bolt going into the head, start the engine when warm and check out the oil flow. If the engine has been sitting for a while, unscrew the rocker arm covers and pour some oil in on the cam, can't hurt. I do this each oil change to make sure that the top end has plenty of lube for startup.

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Hhhmmm....now I've caught up with the other threads on this and ADV about RFVC heads/pumps and malarkies with toasted bikes, I now see it's a known issue.....but that no-one really has put their finger on the big WHY.

Possibly because there is no single big WHY (otherwise Honda would've fixed it) but rather lots of potential ones each of which could be 'it' in a given circumstance....

For example should I be concerned that my oil drains down below dipstick level a fe hours after stopping the engine....something about a valve in the oil pump supposed to prevent that.....well it's been like that for years and still works fine, so maybe not.

Still it feels somewhat like the RFVC oil thing is Russian Roulette - or as my accountant might put it "contingent liability" - until it becomes a realised one!

Bumble Bee approach required - I don't even know I can't fly and fried heads will never happen to me.👍

TDD

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A few others have done that, but I'm not sure of the long term affects at this point. The crankshaft is also fed by the same pump as the head, but I'm not sure what the cranks needs as far as minimum flow. Roller bearings typically don't need much oil volume, but the oil is responsible for a lot of cooling in these engines.

What i`d be worried about HT is if you open up the line to the head the flow to the crank will decrease.and as you say roller bearings don`t need much oil volume...but,,,that oil flow is also to cool the underside of the piston,lube the piston pin,and also provide cylinder wall with oil....and the cylinder wall needs all it can get:lol:

B

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It's also pretty well known that these engines scuff the rod small end fairly quickly....even if it doesn't knock the dimensions out of spec. Reducing lube oil slung from the rod bearing onto the piston and pin is not a risk I want to take when I have yet to nuke a top end. If I can get the information sorted out for a high volume pump option, then maybe.

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I wonder if the whole cilinder and piston is lubed by the flow to the crank alone.

Personally I suspect the oil gathering from different parts in the bottom of the engine is also being thrown against the piston by the crankshaft rotating in it.

I have done a bigger tube to the head, but only drove like 70km's with it until now... I think I'm going to put the old one back as I think it's fine the size it is from factory. However I have drilled the banjobolt holes all the way though so that provides a little more oil to the head. Don't know what the long-term effects will be yet...

I suspect the main reason for oil related engine damage is the oil draining from the frame reservoir by the check valve being stuck/ not sealing well. The oil also drains from the scavenge side pump when engine is shut down as this side doesn't have a check-valve or something.

When starting it takes a while before oil gets pumped back to the reservoir....

If the oil has drained from the frametube, the pump gets no oil and can't lube the head. Also, it may suck in air this way...

Now that I think of it, I can easily test this by disconnecting the return hose to the frame, and leading it to a bucket or something. Then start engine and see when it starts pumping oil back up. 👍

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Something worth pointing out is that the 650R has an oil nozzle that sprays the underside of the piston, providing a lot of cooling and lubrication. If the RFVCs had something like that, I wouldn't be nearly as concerned about reducing oil flow through the crank in order to give the top end more. Unfortunately it would not be a trivial task to do a retrofit and would probably still require a higher volume pump.

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Nice - three informative responses, thanks guys.

After a few very hot desert trips without incident - but noting my vapour head/oil line sensor was indicating the kind of temps that cause oil to begin to break down - like above the 250F mark - I went ahead and fitted an oil cooler and did the big fin mod just to be super sure I was doing everything possible to keep temps down.

So far so good - but looking at that weedy little oil line to the head has me wondering if it could use more flow...not informed enough to make a call on that...could I potentially stuff it up if I installed a wider pipe and opened out the banjo bolt holes a bit??

few pics of the cooler and my making up the big fins and finished job.

IMGP1409.jpg

P1290036-1.jpg

P3160173.jpg

P3160180.jpg

Nice cooler dave

You'd want to get a guard on that baby though - I have a cooler in a similiar position.

IMG_4062.jpg

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Yes Mr 630 I'll be getting some pro ahead of that cooler as soon as I find something suitable...it's been is test for a few weeks check it works OK before I formally adopt it!

next project is CRF front end...bit like yours!

TDD:thumbsup:

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I think it is also a case of such a bulletproof bike, that this is the ONLY thing that ever really goes wrong on this motor. It may be a relative weak point compared to a pretty solid drivetrain, but slso consider that the cam is sort of a wear item, much like a clutch or brake but when it grounds down most see it as a failure. I'm sure many of the premature ones are oil supply or quality issues (overheated), but eventually all cams will need to be replaced. It is often that lobe/rocker furthest from the feed line that fries, assuming that when oil gets low that is the first one to get starved.

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The cam is a wear item, but it should outlast the piston rings in normal operation.

I have thought about modifying the head to accept a two-piece needle bearing for the cam center journal. Problem is that I have been having trouble finding them at all, let alone in a usable size. Only place I have seen them is in photos of the rod bearing in old Tecumseh two cycle lawnmowers. It wouldn't save the rockers or cam, but it would probably keep the head from getting damaged.

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