Topic: worn cam journal solutions

[hymodyne]

I'm in anticipation of a MRieck'd ported head for my 500 overbore project pretty soon. I looked at the condition of my cam cover and the journals are in pretty bad shape. Is there anything I can do to fix the scoring I've found on some of the journal surfaces? I'm looking at another cam cover on feebay, but i'd like to know if I can do anything with the one I have before I pay out for it.

hym

[bwaller]

Any chance you can put up a picture?

[Terry in Australia]

I wouldn't worry about light scoring (deep enough to catch your nail is still only light, in my opinion) as all the scoring will do is hold oil, which isn't a bad thing, but if they're worse than that, or out of round, it might be cheaper to buy another head.

The CB750 was very thoughtfully designed with removeable cam towers so it's not an issue, but a friend of mine had a problem like yours with an XL250 engine back in the 1970's, and he had an engineer make bronze inserts. (he reamed out the old aluminum surfaces and "shrunk" in the bronze inserts)

This apparently, was a pretty common "fix" here in Oz, back then, but nowadays engineers will probably just tell you to source another head, unless you can find an "old school" guy to do it for you, but once again, it'll probably cost a lot more than the EBay item. Cheers, Terry.

[MRieck]

 The head I assume the cover went to had very bad journals. I mean smeared material kind of bad. The head was NG. Considering the condition of the new head (very, very nice) and new parts (all new valves, Kibblewhite springs etc) I'd go for a new cover. The head will be going to the machine shop this Saturday too.....

[754]

I have made inserts for a few Honda singles, make sure you pin them.

A long time ago , Megacycle or someone used to do a needle bearing conversion.. it used a split bearing or race.

A buddy of mine long ago took a 350 or 250 XL motor in a box on his CB 750 all the way from BC to LA to get the motor done by Bill Bell. He had raced one of them with great success in Baja, back in the 70,s. I think that motor is in his Champion frame and is living most of the time in the Trev Deeley Museum for all to enjoy..

[kghost]

ANy chance of having it welded and rebored?

[Terry in Australia]

From memory they're not actually line-bored, due to the shape of the casting.

[kghost]

From memory they're not actually line-bored, due to the shape of the casting.

Well he didn't say how many or where....dunno I don't have a 500/550 but if its just one and on the outside?

[Terry in Australia]

I haven't looked at one for a long time either Tim, but from memory, the cam sits well down in the casting, and because of this they can't be bored, as there's no access for a line boring machine without perhaps punching holes either end of the casting.

[bwaller]

Well if the suggestion is to replace the cover at least hold out for a later model (77 or 78)that locates the rocker shafts. They are not big money, and I don't have a spare but they do appear on E-bay.

[hymodyne]

Thanks for the suggestions. I heard from an ebayer who has a cam cover for sale that is in much better shape than mine. I'm going to pick it up next week and go from there.

hym

[MRieck]

Thanks for the suggestions. I heard from an ebayer who has a cam cover for sale that is in much better shape than mine. I'm going to pick it up next week and go from there.

hym

It's tough to place a price tag on peace of mind.

[kghost]

I haven't looked at one for a long time either Tim, but from memory, the cam sits well down in the casting, and because of this they can't be bored, as there's no access for a line boring machine without perhaps punching holes either end of the casting.

Honda Machined them somehow.

[turboguzzi]

Some honda singles had indeed needle bearing conversions but like people noted, the 500-4 cam journals in the head and cover were made with some high precision fixture that machined the journals from above.

One idea that comes to mind though (hope I'll never need this...) is that with today's very high precision CNC's you could in theory oversize the journals area so that you could fit split bronze bushings.

Somebody will need to do the CNC programming + location and zeroing of the head would be critical, but doable with enough patience and $.

Sounds like a second hand head would be cheaper. would go this way only with a head that has a few dozen hours of porting work on it.

TG

[MRieck]

Some Honda singles had indeed needle bearing conversions but like people noted, the 500-4 cam journals in the head and cover were made with some high precision fixture that machined the journals from above.

One idea that comes to mind though (hope I'll never need this...) is that with today's very high precision CNC's you could in theory oversize the journals area so that you could fit split bronze bushings.

Somebody will need to do the CNC programming + location and zeroing of the head would be critical, but doable with enough patience and $.

Sounds like a second hand head would be cheaper. would go this way only with a head that has a few dozen hours of porting work on it.

TG

Yes TG though only the cover is necessary....to much time and money invested to compromise now.

[hymodyne]

I'm having a good replacement cam cover shipped from IL on Wednesday. Pics I've seen of the inside show minimal wear on all rockers, tappets and journal surfaces; I have a 650 camshaft in good condition and a 650 tach cable.

hym

[yabo]

Worn cylinder head cam sit is a big problem for honda xl250's....
I think best way is bronze split bearings or split needle bearings...
any idea?

[dave500]

#$%*?it took you a year to reply to a five year old post?

[lucky]

I wouldn't worry about light scoring (deep enough to catch your nail is still only light, in my opinion) as all the scoring will do is hold oil, which isn't a bad thing, but if they're worse than that, or out of round, it might be cheaper to buy another head.

The CB750 was very thoughtfully designed with removeable cam towers so it's not an issue, but a friend of mine had a problem like yours with an XL250 engine back in the 1970's, and he had an engineer make bronze inserts. (he reamed out the old aluminum surfaces and "shrunk" in the bronze inserts)

This apparently, was a pretty common "fix" here in Oz, back then, but nowadays engineers will probably just tell you to source another head, unless you can find an "old school" guy to do it for you, but once again, it'll probably cost a lot more than the EBay item. Cheers, Terry.

Some owners of early CB350's actually put in needle roller bearings .

[yabo]

Any experience of split bronze bushings?