Topic: 1975 CB750F Project - Total Rebuild

[Kickstart]

Even if you have the crank work done you may still be able to reuse good bearings once you Plastigage it

I'm also concerned about the bearings though... Here's a link to a thread I started where I asked about the void in my one crank journal.  Towards the end of the thread I attached some close-up pictures of the bearings:
http://forums.sohc4.net/index.php?topic=109588


I'd definitely be interested in your opinion on whether or not I should replace the bearings.

Thanks,
Chris

[Jerry Rxman Griffin aka MuthaF'er]

Chris, I don't think those bearings show much wear. IMO, the scratches, to me, say that something ran through them and exited or were scratched upon assembly. In either case you can see where the crank smoothed down the softer edges and re-mated. The crank is hardened and the bearings are soft. I don't think it's necessary to replace them unless the clearance is excessive. I'd bet they ran fine before without any symptoms? If so what the hell. With that being said I just put together a $7000+ engine that I wanted to be as perfect as possible so yes I replaced all bearings but it probably wasn't "necessary". Just depends on how much more you are willing to spend. Insurance vs expense. If you replace them you could even have an install mishap too. 

Any thoughts from the other guys?? If expense was NOT a consideration would you replace them? If expense IS a consideration would you replace them? Why or why not?

[aperry]

Regarding soda blasting.....when I got my Harbor Freight soda blaster, I thought it was the coolest thing since sliced bread.  I still do actually, but I am starting to wonder whether some of my adhesion issues have to do with this.  I did a lot of research around the time when I was soda blasting the engine, and it seems like the professionals really try to stay away from soda blasting because it's hard to thoroughly clean out of metal surfaces, and I remember reading that many paint brands don't guarantee their paint if the surface has been prepped with soda blasting.

I haven't had any real catastrophes that I can blame on soda blasting.  It's not bubbling or flaking off, but it sure does seem to come off easily when chipped or scratched.  Maybe my expectations are too high, or maybe I didn't clean well enough. These engines sure do take a lot of time to prep!!

Btw, pretty sure I remember reading about a chemical designed to thoroughly clean out the soda from aluminum.  Can't remember the name.  Seem people recommend vinegar, which makes sense if you remember grade school volcano projects.  I did actually try that. 

Also, maybe another blasting medium to look into is walnut shells?  I would think they are softer than aluminum (though I'm sure they can still do damage in other ways).


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[Kickstart]

...
Any thoughts from the other guys?? If expense was NOT a consideration would you replace them? If expense IS a consideration would you replace them? Why or why not?

Well, Hondaman said he'd but it back the way it is... so no, I don't have to replace the bearings.  Although I'm not sure if Mark was assuming polishing the journals or not... and I do want to clean-up the journals (especially the two pitted areas). It's really just me wanting this engine to be perfect... while I'm not throwing $7k at it, I realize that I'm not going to be too far off from that on the total project costs when you add up all the other work and parts.  I just feel like I've got everything apart, why not do it while I'm in here and know it's perfect.  My end goal is I want a bike that I can push really hard and not have to open her up again for 50K miles (basically, I only want to do this once on this bike).  I think I'm talking myself into sending the crank our for polishing and getting new bearings

[Kickstart]

....when I got my Harbor Freight soda blaster, I thought it was the coolest thing since sliced bread.  I still do actually, ...

Which one did you get?  I got the 15lb one and it didn't work at all.  It only spit out powder a couple times and even then it didn't strip anything.  I was trying to clean-up my carbs with it.

I think mine may be defective, as it was obviously returned previously (used Teflon tape on the threaded parts).  I'm planning on returning it, but I'm not sure if I'll get another one.
My air compressor is a little on the light side for it (only 6.2 CFM @ 90 - whereas you're suppose to have 7 CFM).  I also used regular baking soda... maybe the stuff you by in the bags at Harbor Freight works better.

I might just stick just spending a lot of quality time with my engine manually sanding it.

[Kickstart]

Some more progress.

Head and cylinders back from the machine shop.  I'm really quite happy with how it looks.
New APE bronze valve guides installed and the old valves cleaned-up and re-seated (not sure if that's the correct term).

I attached some pictures.  I also did a "dry" fit with a couple pistons and the jugs (I didn't install the rings)... I just wanted to see how high up the Z1 pistons come to the top of the cylinder.

In hindsight, I should have removed the exhaust studs beforehand (or had the shop do them).  I also should have done some head porting and de-shrouding work beforehand as well.  I'm not sure I want to take a dremel tool to the head now that I have the valve seats freshly cut.

[Kickstart]

Few more pictures...

[Kickstart]

I've been working on the carbs for the last 1-2 weeks.

I don't have a before picture, but they were in typical condition for 35+ year old carbs.

I tried to be as thorough as possible:

• Disassembled them as much as possible soaking the non-plastic items in a can of carb cleaner, and the larger parts (bowls, carb bodies) were also were pressure washed (using some simple green) as well as the carb-stay-plate assembly .
• All the holes in the emulsifier tubes were run through with machinist bits, as specified in Hondaman's book.
• Made sure all passages were clean/clear
• Replaced all gaskets and o-rings
• Replaced the valves/valve seats
• Filed the outsides of the brass float hinges and sanded them, as well as the the insides of the float posts, with 1000 grit wet/dry - to make sure there were no sticking points
• Replaced the needle jets / jet needles (although I probably didn't have to do this as I hear they really don't wear that much)
• Increased the main jets from 105 to 110 (purchased new jets from Z1)
• Based on another post I found on SOHC4, I replaced the grommets in the tops of the carbs (where the slide shaft comes out) with grommets I picked up at Lowes and bored out with a Dremel to fit.
• Polished up the float bowls (they were looking pretty rough) and did a rough polish to the carb tops
• Replaced all the vacuum/vent/overflow hoses

Unfortunately, the brass on the choke linkages and some of the screws/bolts is very thin and had already corroded off or came off while I tried to clean them up... so I suspect these wont look good for long.  I also didn't have any cotter pins small enough for these linkages, so I had to reuse the existing ones (or what was left of them).

Overall, I'm pretty happy with how these came out.  I'll be putting them on my running bike shortly, to sync them and give them a good trial run.  My running bike also seams to be running lean, and getting poor gas mileage... so I want to play around with the carbs on that bike as well.

When I do this again (for the next set of carbs) I think I'm going to skip the bucket of carb cleaner.  After cleaning them, I noticed there is a little plastic guide in the side of the carb body used to align the throttle slide... so it's probably not the best idea to soak these carb bodies. Maybe I'll just use the aluminum safe simple green next time, or just wipe them real well with the spray-can carb cleaner.

After I get this wrapped up, it will be back to the engine/crankcase.

[aperry]

Sorry, I missed your question above.  My soda blaster was also the smaller model (15 pound I think).  I had to return the first one I got as it just kept getting clogged.  Even the replacement seems to get clogged somewhat frequently.  I'm not sure if "clogged" is the right term.  It just stops spraying soda.  I've found that if I shake the canister a little bit then it starts again.  I would imagine I have a little moisture in the canister and pockets of air around the internal tube are forming.  By shaking the thing, I think I'm allowing the soda to re-settle around the internal tube.

Btw, I used the soda blaster on the external parts of the carbs too.  They cleaned up really well with it.  I think the soda blaster is just a case of knowing when/where to use it.  I'll probably try to avoid it from now on with parts that I intend to paint.

Your carbs look great!  Engine too.  Can't wait to see the final product.

Aaron

[Kickstart]

Got my parts back from the powder coating place.

I give them a C- right now.
I think they did an excellent job on the actual painting, but they missed tapping off a few threaded parts, and painted a couple of areas I asked them to tape off.  But the worst thing they did was sand blast the inside of my brake calipers where the pistons go.  I have another post on the forum to get opinions on whether or not I can still use them.
http://forums.sohc4.net/index.php?topic=111978


Otherwise, the parts look great.  I had everything done in gloss black except for the calipers, rotors, and top triple bridge which were done in a low gloss black.

[Kickstart]

Making some more progress on the engine.

I know I should have done this before the valve job, but I couldn't resist... I carefully sanded/grinded the head to de-shroud around the valves and do the quench band.

Since my pistons are +1.0, I realized the combustion chambers had a significant lip over the bored out cylinders in some areas.  The quench band work I did was really just removing any extra metal that protruded past the head gasket sealing rings.

Attached are a couple pics.  The one picture shows a comparison of the completed #3 chamber to the #4 chamber which hasn't been done yet.

[Kickstart]

Did some valve deshrouding on the cylinders and started polishing the transmission gears.

Pictures attached. 

The pollishing compound on the gears seams to be staying in place (I'm periodically opening up the case to make sure it hasn't migrated to areas where I don't want it to be).  Looks like I didn't put enough compound on 1st gear (gears), but that one was fairly smooth/pollished already - the bike has 20k miles on it.  On most of the gears I can still see the ridges (and feel them with my fingernail), which I'm trying to pollish off.  I spent 45 minutes hand cranking the gears last night... I'll be doing a lot more this weekend.

[Kickstart]

Making some more progress...

I took a bunch of measurements on my transmission (should have done this before the polishing)... and it looks like the dogs on my M3 gear are not looking so good (for 4th gear engagement).  The witness marks on its mate (M4) measure under 3.5mm (3.44 mm).  So I'm considering getting this gear (or maybe all the gears) backcut.  2nd gear looks great (I forgot what the witness marks measure, but it was good).

I made some good progress on removing the cylinder studs in the upper case and the exhaust studs in the head (I didn't take a picture of the latter).  I decided I want to get HD cylinder studs (because I'll feel better later on knowing I upgraded these), and I want to replace the rusty exhaust studs (because they just look bad.)

I got a tip from my machinist to use a electric griddle to heat the parts before trying to remove the studs.  Using a combination of lots of penetrating oil, heat, slow constant pressure, patience, and a few assists with the vice-grips... I got all the cylinder studs out without stripping or breaking anything off.  So I'm pretty happy with that.

[Cevan]

The soda blasters work much better with real baking soda media instead of the baking variety, which is too fine and packs up. 

[Kickstart]

It's been a while since I last posted.  I lost a lot of momentum over the holiday but I have been busy the last few weeks.

I've been test assembling the cylinder/pistons/head and valve train and taking some valve clearance measurements with different cam advance timings.

I started a thread on some issues I ran into with not having enough clearance (with some good pictures):
http://forums.sohc4.net/index.php?topic=117206
But after some more careful assembly (and using a degree wheel) it looks like I'll be OK.

In hindsight, I probably shouldn't have taken 0.010" off the deck.  I originally thought he pistons were 0.010" inches shy of the top of the deck... I took this measurement after a test assembly of just the pistons/cylinders but didn't consider that everything would fit tighter together after torquing the head down. It looks like pistons were flush the deck, and now sit about 0.010 proud of the deck at TDC.

I might get a thicker base gasket, as I would like an extra 0.010" of valve clearance, and I'm a little nervous about openings in the head gasket overlapping the bores a little. I have a stock head gasket with +1.0mm pistons - which is suppose to work, but it appears like the openings in the gasket hang over the bores ever so slightly in some areas.  (sorry, I don't have a picture).

[Kickstart]

While I had everything out of the boxes... I took some wear measurements of the rockers and rocker shafts.

Picture attached of the 1/2 exhaust shaft.  It doesn't look good, but the shiny spots are only worn about 0.0001".  Everything (including the ID bores of the rockers and towers) measures within spec... so it looks like I'm good to re-use these.

[Kickstart]

I did some work cleaning up the "flashing" on the fins of the head a jugs.

It wasn't that bad before I started, but I figure now's the time to clean it up before I paint the engine.

I cleaned up all the passages in the middle, but I only got a good before/after picture of the left front corner on the head (attached pictures)

[iron_worker]

Heating the case up on electric griddle is a pretty smart idea. Wish I would have done that before I snapped the last stud off. Arg!

IW

[70CB750]

Subscribed.

[Kickstart]

Man, this is slow going.

I spent the weekend trying to clean the cases, jugs, head, etc. to get it ready for painting.

I assembled the whole engine pretty much hollow (with just the valves in place)... with the idea that I might be able to prevent water and blasting media from getting inside.  It' worked pretty well, but the right way to do this would have been to blast everything before doing any machine work.  Oh well... next build.

Here's what I've did:

• Sprayed the whole engine with Gunk engine de-greaser - let it sit for 15 minutes
• Sprayed it down with a pressure washer (just water)
• Soda blasted everything - this worked but not all that well as I only have a 10 gal 120V air compressor - this part took forever
• Sprayed it down again with the pressure washer
• Sprayed everything with Clean-strip paint remover - let that sit for 15 minutes
• Sprayed it down one more time with the pressure washer
• Spent most of this morning/afternoon manually sanding and brushing

Pictures of the end result attached.... I'm not there yet, but I think I'm getting close.
I'm taking everything back apart and will work some more on each part individually with wet/dry and scotch-brite pads.

I think I'm getting there, except for between the fins on the jugs.  I don't think my soda blaster/air compressor was strong enough get all the pant off in there (one of the reasons I hit the hole engine with paint stripper). The head cleaned-up better, I think I managed to remove all the paint from the head.

I used both the Eastwood small job soda blaster and a $19 media blaster gun (with a little hopper on top of it) that I got at Harbor Freight.  The $19 gun actually worked better... as I Eastwood blaster sometimes had trouble drawing up the soda.

Cevan - you're absolutely correct... night and day using the proper soda blasting media versus the cooking variety.

Does anyone have any tips on how to make sure all the paint between the fins on the jugs/cylinders is removed?  I really don't want to paint over old paint.

[Kickstart]

I took apart the engine so I could start working on the separate pieces, but before I split the case I decided to clean-up the base gasket surface (it was looking a little grimy).

I hit it lightly with some 1000 grit, and then some green scotch pads.  There are still some discolored areas, but I didn't want to be too aggressive with a gasket surface.  In fact, I'm not sure if it's OK to use scotch pads on gasket surfaces.

I plan to make some more progress on prepping the cases tomorrow.

[Kickstart]

Wow... it's been a long time.

Well, I got side-tracked this summer - what started with an interest in improving my riding skills, turned into getting hooked on vintage racing. 

http://forums.sohc4.net/index.php?topic=122250.msg1420925#msg1420925

I spent most of the summer prepping my street bike to race.  Then after racing, work got busy and my garage sat in the same state I left it in right before going to the track (basically in a total mess).

OK... time to get the project back in gear.

I'm almost ready to start assembling the engine.  Tonight I inspected the oil pump.  It's looking pretty good.

Rotor-to-rotor clearance measurements on the pick-up side are between 0.0025-0.004".  There are some nicks on the lobes of the inner rotor, but otherwise looks pretty good, and I don't think this is a problem for the pick-up side.

Rotor-to-rotor clearance measurements on the high-pressure side are between 0.0025-0.003".  Inner rotor looks really good.

Both sides have Rotor-to-body clearance of 0.003".  There is some light scoring on the side of the rotors and covers, but I think this is OK. Rubber on the check valve looks good.

I think I'm just going to replace all the o-rings, and the shaft seal, and I should be good to go.  Maybe I'll replace rubber check valve now that someone here is making a reproduction part.

[Kickstart]

OK... oil pump is back together with all new seals and is now primed and sitting in a container of oil.

Getting the oil-pump shaft seal out without damaging the pump was a real pain.  I don't have a picture but I was able to use a small blind bearing puller to get it out.

Moving on..
I modified my clutch hub and cam towers by drilling extra oil holes in them as recommended in HondaMan's book.  Pictures attached.

I'm pretty much ready to start reassembling the engine now.  I just need to re-paint the head, as the Duplicolor engine paint peeled off the top fins when I decided to spray it with the garden hose to give it a final rinse. I have a feeling I'm not going to be happy with the Duplicolor engine paint.  Hopefully it holds up better on the case and jugs.

[Kickstart]

Beginning the process of reassembling the engine.

Picture attached - APE is written all over it

• Balanced crank
• Back-cut gear dogs
• HD bearing studs (I don't remember why I decided I needed these, but I ended up buying them a while back)

I also have all new ball bearings (SKF) except the needle bearings in the primary gear assembly, which are some other brand.  I don't remember the brand, but I do remember the bearing shop saying they were very good quality (not that I would really know).

Well, about those needle bearings.  I think I might have managed to damage one of them when driving it in.  I now notice a periodic grinding/clunking/clacking noise when I spin the primary gear shaft.  So, yeah, that stinks.  I'll have to order another set and try again. 

Except for having to wait for a new set of needle bearings... making good progress.

And, just in case you were wondering... no I don't remember how much all that stuff above cost me. It was all stinking expensive and I decided it's best if I just don't think about it

 

[Kickstart]

Also did a little work preparing the head today.

I slipped on the inlet boots and felt for a smooth transition between the inlet boots and spigots.

1 and 4 were flush, but I both 2 and 3 had ridges/bulges on their insides bends.  So I took a file to them to remove this restriction. It's hard to see in the photos, but I tried to take before and after shots.  You can kind of see the reduced area in the before picture, but it was really noticeable by feel.

I thought I did a really nice job filing, but thanks to high definition cameras I can see that I din't get a perfect curve... I might go back and clean that up a little more