Topic: resurfacing cam jounals on 550k head and valve cover

[cb(r)]

I have a spare complete top end for a  '76? cb550  monoblock the head and cam etc.  I noticed that the cam jopunals on the cam look good but the head and valve cover bores were grooved.  maybe not as bad as I think but none the less my question(s) is:

has anyone repaired or resurfaced the cam journal bores on the head?  does anyone know of anyone that has done this?  any other Ideas? 

[cb(r)]

chirp? chirp?

[cb650]

Dont chirp to loud or Heffys fat assed cat will get you!!
Wasnt there a thread about a place that coated cyls?  Might work. Thought I saved it but cant find it.  Have a head that might be ruined so have been wonderin too.


                   Terry

[Bodi]

Can't think of any realistic way to renew those. I can't figure out how they bored the things originally, let alone how you would rebore them larger to fit bearing shells - and that's the only option I can imagine.
Plastigauge the cam and journals and see if the fit is within spec. If not, you might have some sweet paperwieghts?

[JHansen]

The head and valve cover bores on my cb400 are slightly scored as well. When I asked the machine shop who did my valve job and rebore about this slight scoring and how it would affect engine longevity, he indicated that if the scores we're not deep enough to catch a fingernail and it was meeting the camshaft within tolerance, it would be fine, just keep up on your oil changes. He said my options were to live with this head or shell out 4-600 on av NOS head (yeah, as if you could fine one of those!)

He did indicate that it was possible to machine out bores to fit a bearing shell, but you are talking some serious fabrication work here, and very expensive, also a specialized machine shop with the right equipment and know how on these things.

Have you any pic's of your scoring? I'll bet some of us could relate it to our own cylinder heads and tell you if we would ride on it.

One last thing, my machinist also said, if it made me feel better, I could VERY VERY VERY lightly buff out the bores with a light grade scotch brite pad. again, the word here is VERY LIGHTLY, or you'll do more damage.

I'm running mine on what it is, that'll be me changing the oil every 1000 miles or so, which is OK, saves on gas bills!

[HondaMan]

Well, I haven't done this since 1971:

we rebuilt a high-mileage CB750K0 (120,000 miles) and it was the first time we tried to recondition the cam bearings (and crank mains). It went like this:
1. Align-bore the assembled head through the bearings and caps, then install inserts to fill in the holes or get oversized bearings and make your own oil holes. Be sure to chamfer the oil holes on the cam side (and crank side, down below).
2. Chamfer the edges of the bearings.
3. Polish the cam bearings (crank, down below).
4. Critically align the cam bearings on reassembly, setting for final clearances of .0008" to .001". This will quickly wear to .002". DO NOT run above 5000 RPM for the first 500 miles after this, or you will spin the new bearings.

The oil pump loses 25% of its flow within about 20,000 miles and the result is top-end wear. Running 15-40 or 20-50 oil will reduce this tendency.

I'm trying to find someone in the Denver area who can help me do this to my "big four" this Spring. I'll keep this site posted if I find a good machine shop.

[cb650]

Howbout hard chroming the journals and having them ground then hone the head.




            Terry

[Raul CB750K1]

Or some Vegemite?


Sorry I couldn't help it. 


Raul

[MRieck]

I know somebody that align hones cam bearing surfaces. This is popular in supersport racing to increase the journel to bearing clearance and cut some frictional losses. It isn't cheap and I don't know if it would work for your application. To be honest if the bike didn't experience oil pressure/feed problems I'm sure it's OK.

[MRieck]

Well, I haven't done this since 1971:

we rebuilt a high-mileage CB750K0 (120,000 miles) and it was the first time we tried to recondition the cam bearings (and crank mains). It went like this:
1. Align-bore the assembled head through the bearings and caps, then install inserts to fill in the holes or get oversized bearings and make your own oil holes. Be sure to chamfer the oil holes on the cam side (and crank side, down below).
2. Chamfer the edges of the bearings.
3. Polish the cam bearings (crank, down below).
4. Critically align the cam bearings on reassembly, setting for final clearances of .0008" to .001". This will quickly wear to .002". DO NOT run above 5000 RPM for the first 500 miles after this, or you will spin the new bearings.

The oil pump loses 25% of its flow within about 20,000 miles and the result is top-end wear. Running 15-40 or 20-50 oil will reduce this tendency.

I'm trying to find someone in the Denver area who can help me do this to my "big four" this Spring. I'll keep this site posted if I find a good machine shop.

                Why didn't you just replace the cam towers?

[cb(r)]

I know somebody that align hones cam bearing surfaces. This is popular in supersport racing to increase the journel to bearing clearance and cut some frictional losses. It isn't cheap and I don't know if it would work for your application. To be honest if the bike didn't experience oil pressure/feed problems I'm sure it's OK.

I dont know about the oil pressure because I bought the top end from someone out of town.  The top end is a spare. maybe int the near future I will see if I have the capabilities to do thins.  In the mean time it is good to know that this type of machining is being done. 

[cb(r)]

Oh ya on a side note, raul good to hear from ya.  did you get those cycle pics of my avatar?

[bryanj]

Ah all you 750 bods, on a 500/550 the journals are direct into the head there are no towers( which incidentaly are easy to fix) even worse the head casting covers the bearing bore at the ends of the head so they couldnt have been line bored when new. The only thing i can visualise that could have machined them is a big mill (Horizontal OR vertical) with a bevel driven, at the centre, cutting bar using exact sized cutters where the beariing surfaces are. Now i have NEVER actualy seen anything like this i was just trying to figure out HOW. As to a fix as all 500/550 heads are the same a good used one is the best option OR Mr Silver did have some NOS at £150 ($280?) which when you consider the machining and the original cost is a steal

[cb(r)]

Ah all you 750 bods, on a 500/550 the journals are direct into the head there are no towers( which incidentaly are easy to fix) even worse the head casting covers the bearing bore at the ends of the head so they couldnt have been line bored when new. The only thing i can visualise that could have machined them is a big mill (Horizontal OR vertical) with a bevel driven, at the centre, cutting bar using exact sized cutters where the beariing surfaces are. Now i have NEVER actualy seen anything like this i was just trying to figure out HOW. As to a fix as all 500/550 heads are the same a good used one is the best option OR Mr Silver did have some NOS at £150 ($280?) which when you consider the machining and the original cost is a steal

I think you might have given me a great idea.  when I get home tonight I am going to take a closer look at the set up.  there might be an easier way to do this. I will get back with ya later. 

[crazypj]

Hand scraping as they do on machine ways. time consuming and expensive to have done. The 400/500/550 cannot have line bored cam bearings so it shouldnt matter if you swap things about ( but use plastigage to check clearance)
 Personally I'd just polish high spots down and not worry about small grooves, extra oil retention devices
PJ.

[cb(r)]

hand scraping.  wow that could be a very good idea.  I am not proficient at it but then again there are not to many out there that are.  nver the less this might be a feasible solutions.  I only worry that there is not enough total surface material to be effective?

[HondaMan]

                Why didn't you just replace the cam towers?

At the time, they were 2 weeks away and we only had 4 days to do the rebuild. The machine shop was available, and we wanted less clearance than stock (which comes in at about .003" or more), for oil pressure reasons. The user wanted to run 10w40 oil instead of something heavier, so we had to increase the flow to the crank somehow, while we cut tiny "spreaders" into the cam journal bearings to help even out the flow. Even if we had used new towers, we would have had to either orifice the oil feeds to them (risky) or align-bore and insert bearings, anyway, just to get it to go to the crank. Plus, the cam was going back in, and we had it polished first, which reduced the bearings to be almost .008" clearance, which is the service limit, according to Honda. Too much clearance.

It took about 4000 miles before the bike would rev easily, but the last time I saw it, there was another 50k+ miles on it and it ran real sweet at 9000+ RPM. Guess we got it right.