Topic: Someone F'ed Up: Media Blast Over Cam Journal & Gasket Surface

[Trad]

I came across this 550 head while combing Ebay. It's a semi-refinished head but I noticed that the cam journals and gasket surface were both media blasted. I hope no one buys this and plans to use the head core. What a waste.


http://www.ebay.ca/itm/Honda-CB550-500-Re-conditioned-Cylinder-Head-CB550k-CB550f-super-sport-Cb500-/221291438026?pt=Motorcycles_Parts_Accessories&hash=item3385ff5fca&vxp=mtr&_uhb=1

[754]

Better gasket grip. Old trick.
 Not convinced the journalsare finished, it should infact tighten it up if its loose. I would not worry..until you get a cam in there that wont turn freely. Could be wrong..but dont write off the head ..just yet..

[Trad]

Better gasket grip. Old trick.
 Not convinced the journalsare finished, it should infact tighten it up if its loose. I would not worry..until you get a cam in there that wont turn freely. Could be wrong..but dont write off the head ..just yet..

I don't know man. My brother is a machinist by trade and he has stressed that a gasket surface should be as smooth as possible, a mirror finish is most ideal. Those journals are 100% blasted over. Take a look at the fifth photo in. No polish on the journals or factory machine marks on the tops of the journals, just a matte finish. You couldn't pay me to run this head.

[Tews19]

Frank, 754, is a guru... Not doubting your brother but Frank is a pro

[Trad]

Here is the journal surface. I'm not doubting he knows his stuff (I've read some great posts from him) but look at this journal!!!!! haha so messed up. This should be smooth, almost a mirror polish.

[spazz1984]

Sorry I've never rebuilt a head on a bike. wouldn't there be a bearing there aways

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[Trad]

Sorry I've never rebuilt a head on a bike. wouldn't there be a bearing there aways

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The camshafts on these bikes ride directly on the head cam journals without a bearing. The bottom end has bearings.

[754]

I am not a guru.  But you know this looks bad, but may not be
 When big bore base gaskets n 750s have a habit leaking, the soution is this.. Blasrpt it to help contain the gasket.  One guy i knew would punch little dmples around the case/barrel where the oil goes up.. His motors were very oil tight..
 If that head is run, there wil, be abit of material comes off as it beds in, if it turns and has slight clearance, it may be ok.

[spazz1984]

Sorry I've never rebuilt a head on a bike. wouldn't there be a bearing there aways

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The camshafts on these bikes ride directly on the head cam journals without a bearing. The bottom end has bearings.

Ok
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[spazz1984]

Sorry I've never rebuilt a head on a bike. wouldn't there be a bearing there aways

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The camshafts on these bikes ride directly on the head cam journals without a bearing. The bottom end has bearings.

Ok
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[iron_worker]

I wouldn't be too worried about the gasket surface but blasting a bearing surface seems like a bad idea.

Too me, it seems like you should have as smooth of a surface as possible for bearings to promote an even oil film all the way around. After blasting you'd essentially have a low point directly where the bead hit and then a raised  circle around it... so you'd have a "cratered" surface if you looked under magnification. I would be weary of those high points acting more like oil scrapers and causing wear on the cam ... though the cam is a much harder material than the bearing seats.

Either way, I'm no expert and I haven't tried it. When I had my cases blasted I made sure all the bearing surfaces were protected.

IW

[lucky]

It is not a problem.

Mirror finish gasket surface! LOL...lol

Oh brother!

[lucky]

Sorry I've never rebuilt a head on a bike. wouldn't there be a bearing there aways

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The camshafts on these bikes ride directly on the head cam journals without a bearing. The bottom end has bearings.

Many modern small engines have aluminum connecting rods running directly on a steel crank journal with no bushing.

[chickenman_26]

I wouldn't be too worried about the gasket surface but blasting a bearing surface seems like a bad idea.

It's a horrible idea. The gasket surface? No issues. But he should have taped off those journals before blasting. Bead blasting doesn't add metal, so the cam fit will not be tighter than it was. It'll likely be exactly the same as it was. But after the cam polishes those journals smooth again, and it will, the bearing clearance is likely to be excessive. If this head used bearing insert shells, it would have been a different story. He should have used vapor or soda blasting if he wanted to do the bearing journals. Even then, I'd avoid it. Clean those areas chemically. And if that head has blasting beads trapped in the oil galleys and passages and it's not purged, there's going to be a lot of damage real fast after first start.

Stu

[Trad]

I wouldn't be too worried about the gasket surface but blasting a bearing surface seems like a bad idea.

It's a horrible idea. The gasket surface? No issues. But he should have taped off those journals before blasting. Bead blasting doesn't add metal, so the cam fit will not be tighter than it was. It'll likely be exactly the same as it was. But after the cam polishes those journals smooth again, and it will, the bearing clearance is likely to be excessive. If this head used bearing insert shells, it would have been a different story. He should have used vapor or soda blasting if he wanted to do the bearing journals. Even then, I'd avoid it. Clean those areas chemically. And if that head has blasting beads trapped in the oil galleys and passages and it's not purged, there's going to be a lot of damage real fast after first start.

Stu

These were my thoughts when I first saw this. Blasting those journals were essential death to the head not only for cam damage but for cam clearance and oil pressure issues.

As for the blasting. I have blasted cylinder heads in the past but I sure as hell make sure bolts are threaded in and the oil galleys are covered. I then pressure wash and compressed air to make sure no media is trapped. It is then purged again. This is my opinion the best way to get that job safely accomplished.

[lrutt]

all conjecture at this point. Hit it with some 2k wet dry to just take the dull out the assemble and plasti gauge it. I'd bet it's ok. Just be good with the assembly lube and make DAMN sure you get the oil passaged clean. That's where you'll get hosed, that grit going into those journals.

[bjbuchanan]

I wouldn't be too worried about the gasket surface but blasting a bearing surface seems like a bad idea.

It's a horrible idea. The gasket surface? No issues. But he should have taped off those journals before blasting. Bead blasting doesn't add metal, so the cam fit will not be tighter than it was. It'll likely be exactly the same as it was. But after the cam polishes those journals smooth again, and it will, the bearing clearance is likely to be excessive. If this head used bearing insert shells, it would have been a different story. He should have used vapor or soda blasting if he wanted to do the bearing journals. Even then, I'd avoid it. Clean those areas chemically. And if that head has blasting beads trapped in the oil galleys and passages and it's not purged, there's going to be a lot of damage real fast after first start.

Stu

Blasting actually would tighten up the clearance. Those micro valleys and mountains created by the material tighten up clearance, you can look it up it is factual. Now of course polishing to have a good surface would remove more material for a sloppy fit but 754 was correct. I would want a smooth bearing surface if it were me tho

[Trad]

How much of the bearing surface was blasted away and what is the new clearance? A  professional would have taped over the journals and oil passages. Not a big deal with the gasket surface though, that should be fine. You can have dirty junk and you can have clean junk, who knows what the actual condition is. Personally I'd pass due to the ignorance imparted to  the journals.

He blasted the whole thing.

I knew this would be a fun topic to converse on. haha

[Lostboy Steve]

Better gasket grip. Old trick.
 Not convinced the journalsare finished, it should infact tighten it up if its loose. I would not worry..until you get a cam in there that wont turn freely. Could be wrong..but dont write off the head ..just yet..

I agree. Depending on what media was used it may actually function like a BRAND NEW casting as some media only etches surfaces and doesn't really rip them apart. Honestly, I would worry more about what it looked like before blasting (easier to judge wear).

[Lostboy Steve]

Thinking even more on it, after a good mic, this may be a great candidate for some MICRO SLICK coating. Either way he wants way too much coin. I'd rather buy a beat head and redo it myself.

[MRieck]

I wouldn't worry about the journal surfaces. You can wipe them with a scotch brite pad. The bead does lift the surface a bit but after running it for a few minutes it will polish out. There is generally plenty of cam journal clearance on the 550's and 750's.

[Powderman]

I wish Trad was selling the head if I needed it. I would use all his reasoning to bring the price down on that "junk" head and get me a good deal on it. I agree it depends on what media was used. If it was glass bead blasted I would have no issue with what was done. Vapor blasting would have been ideal.

[754]

Or walnut shells or plastic..

[Trad]

I wouldn't be too worried about the gasket surface but blasting a bearing surface seems like a bad idea.

Too me, it seems like you should have as smooth of a surface as possible for bearings to promote an even oil film all the way around. After blasting you'd essentially have a low point directly where the bead hit and then a raised  circle around it... so you'd have a "cratered" surface if you looked under magnification. I would be weary of those high points acting more like oil scrapers and causing wear on the cam ... though the cam is a much harder material than the bearing seats.

Either way, I'm no expert and I haven't tried it. When I had my cases blasted I made sure all the bearing surfaces were protected.

IW

I am going to bring up this point again. I have always been taught that a cam bearing surface or journal should be as smooth as possible to promote even lubrication on the contact areas. Most media blasted surfaces will likely look cratered and the high spots will cause expedited wear on the cam.

If they were polished smooth again I would suspect they would out of spec and you'd have yourself some low oil pressure due to the amount of material removed.

Heck, I could be out t lunch and maybe this is acceptable but I sure a hell wouldn't take the chance.