Honda xl250r cam journal problem

[guest1931]

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....

[steveD]

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

[guest1931]

OK.I'l do it in friday. report it

And hate of this fucking captcha's

[Propellor]

Hi y'all.

What surface finish and clearance do we aim for with these components?

Cheers

[guest1931]

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!

[Propellor]

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!

[steveD]

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!

[Propellor]

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.

[Propellor]

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.

[guest1931]

dear  Propellor
this are manual pics:

[guest1931]

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...

[Propellor]

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?

[guest1931]

Unfortunately I HAVE TO repair.
No way for me to send money to ebay etc...

[timbo]

Hi guys. If anyone's interested, I have a genuine Honda XL250R workshop manual in first class condition. £25 including postage. Just pm me.

[guest564]

Was the cam refinished as well? a worn cam will kill a new bearing surface quite quickly.