Thumper Club Forum
Technical => Bike Problems/Questions => Topic started by: guest1931 on February 01, 2015, 06:44:29 PM
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Hi!got a 1982 honda xl250r, this have all xl's traditional problem: worn cam journals.
I have to repair it.
I build up the journal by al welding and new bore: result was bad.worn fast
I'm not sure making phosphor bronze journals would be a true repair....
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If you can overbore the journal area and then make some plain phosphor bronze bushes (in 2 parts). You will have to peg them to make sure that they do not rotate. Drill for the oil ways, you should be alright. Much better than the plain bearing in the head itself.
Just my thoughts
Steve
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OK.I'l do it in friday. report it
And hate of this fucking captcha's
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Hi y'all.
What surface finish and clearance do we aim for with these components?
Cheers
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For cam shaft:
Check the O.D of journals.Service limits are :19.9mm and 23.9mm
For cam shaft journals on cylinder head:
Check the I.D of bearings(cam journals on cylinder head).Service limits are:20.05mm and 24.05mm
This info source is Honda xl250s 78-81 xl250r 82-83 shop manual.
about finishing I'm not sure but I'll make it as smooth as I can! ;)
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For cam shaft:
Check the O.D of journals.Service limits are :19.9mm and 23.9mm
For cam shaft journals on cylinder head:
Check the I.D of bearings(cam journals on cylinder head).Service limits are:20.05mm and 24.05mm
This info source is Honda xl250s 78-81 xl250r 82-83 shop manual.
about finishing I'm not sure but I'll make it as smooth as I can! ;)
Are they saying
150 microns? (About 6 tho) sounds baggy!
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Yeah but work it out, there needs to be a gap to allow oil to get in and it's pressuriseed. So you are only getting 3 thou per side, not a lot really when you take into consideration expansion. The cam could expand by a couple of thou easily!
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Yeah but work it out, there needs to be a gap to allow oil to get in and it's pressuriseed. So you are only getting 3 thou per side, not a lot really when you take into consideration expansion. The cam could expand by a couple of thou easily!
Fair comment.
I'd expected that the clearance would be taken as a percentage of the journal diameter and reasoned that the camshaft isn't that big. The load will shift orientation (I guess?) so maybe the seemingly excessive clearance is to accommodate a small orbiting motion?
Regarding expansion, ok the cam will generate some heat, but the aluminium cylinder head will be damn hot too and ally has a greater coefficient of expansion than steel. No?
Mehranx, what clearance did you achieve?
Cheers guys.
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http://www.epi-eng.com/piston_engine_technology/engine_bearings.htm
I've not had chance to read the above yet, but thought it might be of interest to us. Ive read other articles from this site (on understanding piston/conrod basics) and found it really good. It helped!
The picture of the bearing shows that the clearance is not evenly distributed, but offset.
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dear Propellor
this are manual pics:
(http://www.axgig.com/images/70881717478492557063_thumb.png) (http://www.axgig.com/viewer.php?file=70881717478492557063.png)
(http://www.axgig.com/images/19491119096550656692_thumb.png) (http://www.axgig.com/viewer.php?file=19491119096550656692.png)
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Yeah but work it out, there needs to be a gap to allow oil to get in and it's pressuriseed. So you are only getting 3 thou per side, not a lot really when you take into consideration expansion. The cam could expand by a couple of thou easily!
PLEASE explain me by easy english. I'm so sorry... :'(
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dear Propellor
this are manual pics:.......
Thanks for the photo mehranx. My interpretation of the information is that we are allowed a service limit clearance (diametral clearance) of 0.150mm on both the left hand and right hand journal. By definition this is not the original clearance, when the bike was new. I'm not sure what clearance to aim for. That was one of my questions. Anybody else know?
Apologies if you already know the following, but in case you don't, a thousandth of a millimetre is a micron. A " thou" is a thousandth of an inch in engineering terminology, over here.
We know the Japanese get these camshafts to run very satisfactorily in aluminium, indeed they have made an art of it, so for yours to have failed something must be different. Stating the obvious!
Is it surface finish, clearance, alignment or because the grade of aluminium is different? Or a combination of all those factors.
My point being that if one of the first three is the reason, then it is possible that even with a bronze bush you might still experience a mechanical failure.
Cheers.
Edit: is the oil pump delivering a good supply of oil to the top end?
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Unfortunately I HAVE TO repair. :'(
No way for me to send money to ebay etc...
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Hi guys. If anyone's interested, I have a genuine Honda XL250R workshop manual in first class condition. £25 including postage. Just pm me.
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Was the cam refinished as well? a worn cam will kill a new bearing surface quite quickly.
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Here you can see my job.hope to work
First of all I decreased the diameter of cam shaft by a grinding machine to 21.8mm.
Then I made a phosphor bronze bushing,I.D is 21.8(+0.05mm).This bushing splits by a hand saw.
(http://www.axgig.com/images/59145425112928155488.jpg) (http://www.axgig.com/)
(http://www.axgig.com/images/75069744947664841742.jpg) (http://www.axgig.com/)
(http://www.axgig.com/images/77485426143143635637.jpg) (http://www.axgig.com/)
(http://www.axgig.com/images/15372037009877029996.jpg) (http://www.axgig.com/)
(http://www.axgig.com/images/99017732517690763713.jpg) (http://www.axgig.com/)
(http://www.axgig.com/images/11038478899835213474.jpg) (http://www.axgig.com/)
I tried to fasten/bind the phosphor bronze half-bushing by mean of a retaining compound... most exciting point.whish to work
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Tolerances sound ok. Good luck!
Is the scroll necessary?
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Have you considered fitting a small peg to stop it from rotating?
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Dear steveD,
You are right.A peg is a safe lock and a standard method.I tried to find out a stiff and small peg to avoid probable movement,but I do not know how.
It's a not a thick bushing,so shocks would loose the peg(pin).It experienced by some experts.Here I wish the individual retaining compound fixes the bushing.
do you have any comments?thanks.
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Great bit of engineering. Really enjoying this thread, and learning a bit as well, so thanks :)
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...
do you have any comments?thanks.
I've been following this thread with interest and I wish mehranx good luck. I hope you get a good result!
The observations I have are:-
The new bush will need a good concentric seating in the head with the most contact area possible to support the bush and give the best chance for the loctite to work.
The clearance between bush and shaft looks about right IMO, but I'd worry about the roundness once it is cut.
The main worry I have is that oil will surely leak quite badly out of the slots left by the cutting in half.
I don't expect the loctite will hold out, but I have been wrong before!
To get a perfectly circular bush, in two perfect halves with no gap in the joint, of that very narrow wall thickness is a very difficult challenge, to say the least!
The very best of luck mehranx.
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Thanks allot friends,I'll check and report the result...
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If you're successful there methranx your could have the makings of a viable business.
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What about using some kind of 'tab' like on a car's main bearing shells.
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The biggest problem is that you have made a bearing and then split it by hacksaw. This is fine for a slow speed bearing NOT under pressure.
You will lose oil pressure through the gap, which will loose oil pressure to the rest of the engine.
Steve
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The biggest problem is that you have made a bearing and then split it by hacksaw. This is fine for a slow speed bearing NOT under pressure.
You will lose oil pressure through the gap, which will loose oil pressure to the rest of the engine.
Steve
Yip, that's exactly my take on things Steve.
I can't see any oil feed holes anywhere either, which is puzzling.
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I have just had a look at the manual and it says that the bearings can be replaced by needle roller bearings, which leads me to think that there is NO pressure feed to the plain bearing surfaces! In which case how is the camshaft lubricated?
I haven't got a head to examine so tis is purely speculation, but the lubrication can be only from 'splash' in the area. In which case it will not make much difference to have a gap in the 'shells', which may help lube in that area.
Just my thoughts.
PS I have got my RS working and MOT'd, looks good but too busy to get it out for a ride :-\
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Maybe the oil is fed up a stud and into the end of the camshaft.
The end bearing could take a straightforward needle bearing but the other bearing would need to be a split bearing because it is trapped between the cam and sprocket mounting flange. Unless the flange is machined off.
're oil pressure . If the little hole I see on the photo is for oil feed then it maybe is just restrictive enough to maintain pressure upstream even if switched to needle bearings? This is pure guesswork however! I can't see the standard setup relying on splash.
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Now,the engine completed montage, first testing was ok during two 10 minutes in 1200 rpm.
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First riding test don,every thing is ok,just a little noise due to cam and new plain bearing.
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Excellent. I have been following this thread with interest.
At least this is real world and has a value EH!
As soon as I can get at my RS I'm gonna take the top end off just to have a look at this.
Steve
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What's the point in that?? "get a life and go ride your bike"
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Congratulations mehranx on what seems to be a success.
Well done! :)
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I have just had a look at the manual and it says that the bearings can be replaced by needle roller bearings, which leads me to think that there is NO pressure feed to the plain bearing surfaces! In which case how is the camshaft lubricated?
I haven't got a head to examine so tis is purely speculation, but the lubrication can be only from 'splash' in the area. In which case it will not make much difference to have a gap in the 'shells', which may help lube in that area.
From what I recall the oil comes up one of the stud holes and in through the end of the camshaft, then out through holes in the cam in the bearing areas. The pressure is very low but the casting around the lobes forms 'buckets' which the lobes pick up oil from, these 'buckets' ensure that there is plenty of oil on start up.
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Hi
In the first 200km run every thing is ok,noise decreased,unbelievable!
I already checked the oil frequently in sequence so far.My method is drip engine oil on a white paper,waiting for a minute lets oil absorbed by paper.Metal particles,chips or such stuff remains on paper face,which can be seen or sensed by finger touch.I wonder if I find phosphor bronze particles.But result is:no kind of particles,yet.
This oil should be checked after a running time for a accurate test.
There is just a noise due to extra valve clearance.After 1000 km this would be adjusted.