The CB750 FAQ contains a compendium of CB750-specific technical information from the SOHC/4 forums.

Oil Change Tips & Tricks

The CB750 is the only SOHC/4 model with a dry sump. As a result, the oil change process is more involved than just removing the sump bolt since you need to drain the oil tank as well.

Excellent set of instructions posted by Jonesy:

Here’s how I do it (FWIW…)

  1. Start up bike and let it run for about 10 minutes. This warms up the oil and gets things roiled up inside, but not so hot you’ll burn yourself. This helps lets the oil pick up crud and let it drain away with the oil, rather than having it settled out and stay in the engine.
  2. After the bike is warmed up a bit, shut it off and put it on the center stand.
  3. I start with the oil tank first. I remove the sidecover and temporarily undo the rear brake light switch to get it out of the way. I also crack the filler cap. Have a drain pan ready and remove the plug. I have a piece of aluminum that I bent into a small trough to keep the oil from running all over the frame.
  4. After the tank is drained, replace and tighten the plug. Proceed on to the oil pan plug and drain the oil from there. Again, replace and tighten the plug.
  5. With the oil pan plug out, kick the engine over a few times to pump out the remaining oil.
  6. Lastly, remove the oil filter housing. If all the parts are in the housing, there is a thin washer between the oil filter element and the spring. This likes to stick to the filter and before you know it, you’ve thrown it away. (This is probably why 90% of them are missing) In other words, when you remove the innards, don’t lose it!.
  7. Wash out any sludge or particulates that have collected in the oil filter housing. Take a good look at what’s in there, as any sizable bits of metal might be a warning that something’s on it’s way out. In some cases it’s worthwhile to drop the oil pan to give it a good cleaning and look for any signs of trouble.
  8. If you bought an oil filter kit that includes new O-rings, fit the small O-ring on the oil filter bolt and seat the big O-ring in the groove of the filter housing. Apply a bit of clean oil to the oil filter bolt O-ring to make it easier to reinsert into the housing.
  9. With the bolt back in place, reassemble the oil filter housing with the spring first, then the washer and finally the new filter. Reinstall the filter on the engine, being careful not to overtighten the bolt.
  10. Reinstall the sidecover over the oil tank and put the brake switch back in place.
  11. Fill the oil tank with 3 quarts of oil. According to the owner’s manual, the oil level will settle into the correct range when the engine is started. So far, I’ve found this to be true.
  12. I like to hit the starter a few times with the emergency stop switch off to circulate the oil into the empty filter housing before running the engine. After doing this, fire up the bike and make sure the oil light goes out in a few seconds.

Again, this is how I like to do it. It doesn’t HAVE to be done this way, but I hope it’s helpful.

From jaknight:

If you happen to want or need to drop your oil pan (I obviously don’t know how familar you are with these bikes), just a heads up to keep track of what holes the different bolts come from; they do vary in their length.

If you happen to need the torque specs for the different bolts:

OIL TANK DRAIN PLUG 24 FT LBS (ideal median)
OIL PAN BOLTS 7 to 10 FT LBS (pick your median)

From toycollector10:

On an older bike you will probably have a lot of gunk sitting in the bottom of the oil tank.

After you have drained the oil put a screwdriver down there and see what you bring up stuck to the tip, and use a flashlight to have a look inside the tank. If it is a mess down there I recommend you pull the tank off the bike and clean it out properly.

and Hondaman:

Although the torque on the oil bolt is listed at 20 ft-lbs: for many years, I’ve only tightened them to (snug + 1/8 turn). This works out around 7-8 ft-lbs on a T-wrench. I’ve always done this because the oil filter housing distorts and locks that $%#*! bolt in something awful, often causing its destruction the next time around.

…just some experience. It won’t leak if your large o-ring is new…

CB750 Engine Changes

This table of CB750 engine modifications was compiled by Axl Griessman at satanicmechanic.org, and is based on Reinhard Hopp’s book, “Honda CB 750 - Die Geschichte einer Legende”.

Engine # Changes
CB750E-1000001 K0
CB750E-1000140 Bolt at the final drive changed from M8x80 to M10x82
CB750E-1000220 new lower case, engine case only available as set
CB750E-1000425 Transmission changed for better shifting
CB750E-1001081 new crankshaft
CB750E-1001760 7 instead of 8 clutch disks
CB750E-1003528 new final drive shaft and sprocket
CB750E-1005307 fixed right bearing of main tranny shaft
CB750E-1007220 new lower case, deeper oil pan
CB750E-1007415 introduced circular opening in lower case
CB750E-1007500 End of sandcast engines
CB750E-1009554 finned oil filter casing
CB750E-1010336 cam holders with additional oil passages, new rocker shafts and valve cover
CB750E-1014996 new exhaust valve guides, new valve guide seals
CB750E-1026144 new cylinder head, cylinder block: new central M6 bolt, cyl. block w/8 rubbers i/o 12. Case with guard to prevent damages from broken drive chains. New sprocket cover, new shift mechanism w/11 parts i/o 7
CB750E-1042806 weaker clutch springs
CB750E-1044813 K1
CB750E-1044805 new case, final drive 18/48 i/o 16/45 or 17/45, chain oiler
CB750E-1044812 carbs w/links i/o individual cables
CB750E-1044968 improved neutral position
CB750E-1056080 new clutch basket
CB750E-1064903 introduced special washerless bolts
CB750E-1068376 cramp for scavange hoses
CB750E-1071336 fuel hoses 5.5mm dia. i/o 5.0mm
CB750E-1113723 grooves in gear shift drum changed from 0.5mm to 1mm for 4th and 5th gear
CB750E-1114461 new head gasket
CB750E-2000001 K2
CB750E-2061311 shorter oil hose w/white mark. Main jets 110, smaller cutouts in air filter case
CB750E-2200001 K3
CB750E-2200001 new cylinder head, new valve guide seals, improved oil passages to camshaft, new piston rings (three part oil scavenge rings), new cam chain guide, larger piston pin circlips, new final drive shaft, new sprocket cover
CB750E-2228679 new cylinder head, new valve guides, new valve guide seals, no more rubbers between fins
CB750E-2300001 K4
CB750E-2304501 new cylinder block, smaller cam chain tunnel
CB750E-2352923 new cylinder block
CB750E-2348093 crankcase mission cover now has gear indicator
CB750E-2372115 K5
CB750E-2428762 K6
CB750E-2470427 clutch almost indentical to F1: new clutch basket, new clutch cover and chrome cover
CB750E-2434657 to CB750E-2439607 new gear shift drum, new center shift fork for improved shifting. New gears on countershaft w/bronce bushings, new case
CB750E-2700001 K7 - carbs w/accelerator pump, shorter intake rubbers, new final drive shaft, sprocket w/center bolt, wider chain line (as F2), final drive 15/41, new clutch, new camshaft (as F1), new pistons (as F), compression ratio 9.2/1. New transmission: 4th gear 1.133 i/o 1.087. Final drive gear 50 teeth i/o 56 (as F1), primary drive 1.985 i/o 1.708
CB750E-2719530 new valve guides
CB750E-2719997 new cam carriers (as F2)
CB750E-3000001 K8 - new intake and exhaust valves, new valve spring retainers and cotters
CB750E-3021913 new cylinder block w/larger cam chain tunnel
CB750FE-2500004 F1 - new camshaft, carbs w/additional idle air. New pistons, compression ratio 9.2/1. New case w/o primary chain oiler. Final drive gear ratio 43/50 i/o 48/50. 4th gear on main shaft 31 i/o 30, 5th gear on countershaft 31 i/o 32
CB750E-2600014 & CB750GE-1000014 F2 - new cylinder head with bigger valves (34/31mm i/o 32/28mm), larger combustion chamber, larger carb mount rubbers, stronger cam chain, new camshaft, stronger valve springs, new retainers, cotters, new pistons compression ratio 9/1. New rod bigend bolts and bearings, stronger clutch springs, additional fins on crankcase, larger fins on oil pan, “oil cooler” - finned plate between oil filter case and engine. Final drive 15/43 or 14/43.
CB750E-3100001 F3

CB750 Engine Removal and Replacement

Quote from: jdigga on June 08, 2007, 11:19:07 PM

So the weeping from my fins is at the point where stuffing half a Shop Towel in between isn’t enough to stem the spray. I’m a bit tired of having to wear a specific pair of oil-stained riding jeans, so it’s time to make the necessary repairs.

I started the tear-down around 5:00pm. Most everything came off without any problems. I did have to use an impact driver on the front sprocket cover and found to my dismay that the sprocket bolt was loose! Luckily it appears that the cover has a little shaft on the inside to keep the bolt in check. I also discovered that the rear brake splined shaft is slightly bent, but it functions just fine.

I knew the actual removal of the engine would be challenging, but I had no idea what I was in for. I tried putting the bike on its ride side but I could get the right angle to pull the frame off. The engine was getting hung up everywhere, and as soon as I’d release one spot, it would hang up somewhere else. I must have put the bike upright and back down again half a dozen times.

By now it’s around 8:30. Took a breather for dinner and browsing this forum for some tips.

Went back out for one last attempt before calling it a night. The bike was on its side and while staring at it I realized the engine wasn’t going to come out that way.

I put it back upright on the centerstand and broke out my set of lady fingers. Shoved one in the lower right rear mount hole, one underneath the rear of the engine, and one in the upper right rear mount hole to act as a handle. Pried the rear up to clear the lower mount. Pulled up the front of the engine to move it towards the right a bit. Basically I walked it out of the side, front-back-front-back.

Turned off the garage lights and closed the door at 10:30pm.

In the process of putting the bike down so many times, my points cover took a beating (even though I put it down on those rubber puzzle mats). The right bar on my clubmans is pointing slightly more downward than the left. I forgot that I left my key in the seat lock and it broke off–I was able to retrieve the bit inside the lock, but I only have one key.

Honda made a huge access improvement in 1979 with the DOHC bikes. The lower right frame rail is detachable and the engine pretty much falls right out. I pulled my other engine the other week, and other than it being a heavy SOB it was hardly a challenge.

And to think I’m only 1/4 of the way there. I still have to take the engine apart–I have no doubt I’ll run into problems there. Plus all the cleanup of old sludge buildup and repair the busted up bits. Then put it all back together again. Don’t get me wrong–I love tinkering with my bikes and learning about them. But sometime it’s just frustrating as hell. I’ll feel better when I’m back on the road again.

Just had to get that off my chest…

Before you put it back in….there is a flange on the motor mount on the lower right side. Grind or file the top of the flange off to the height of the rest of the mount, then shoot a bit of paint on it. This makes the whole assemble-disassemble job MUCH easier. This little flange has probably left several notches in the rib on the bottom of the engine where the bolt goes thru, which can actually jam the engine so badly on the way out as to require a frame cutout to unjam the whole thing (don’t ask me how I know that….). But, removing this tiny little flange top will prevent all of this…

Henry Abe 900cc Piston Rings (CB750)

Quite often the guys that have the 900 Henry Abe kits for the 750′s are looking for ring sets. I just got off the phone with Ed at Total Seal (www.totalseal.com) I shipped my 4 NOS Henry Abe pistons to him to fit or cut & fit for 3 piece oil rings. The good news in that Total Seal can supply all 3 rings (top, 2nd, and 3 piece oil) without cutting the piston. Henry Abe made 2 different 900 pistons however and my qualifier here is that I have the smaller/lighter of the 2. Axel’s site (www.satanicmechanic.org) lists my pistons as the slipper type.

Here are the Total Seal part numbers:

Top Ring 203778
2nd ring 201336
Oil Ring, 3 piece 001549

Hope this can help others.


Gearing Chart

This spreadsheet can be used to calculate gear ratios for your CB750.

Service Bulletin Index

Bulletin Number Issue Date Subject
Recall Letter 08/13/1971 Safety Recall of pre-K1 CB750’s to modify the drive train to reduce drive chain shock loading and extend drive chain life.
750 #4 09/22/1969 Drive Sprocket Factory Recall
750 #6 11/3/1969 Tachometer Gear Stopper Bolt Security to Prevent Cylinder Head Damage
750 #7 10/17/1971 Wing Bolt Retaining Nut Security - Early CB750 Air Cleaner Covers
750 #8 11/6/1969 Ignition Timing With Bent Advancer Shaft
750 #9 05/07/1973 Vacuum Guages: Model Differences and Calibration Instructions
750 #10 12/10/1969 Dead Batteries - Loose Alternator Rotor Set Bolt
750 #11 11/01/1971 Brake Lever Free Play Adjustment
750 #13 01/26/1970 Modification to Prevent Oil Filter Case Damage
750 #14 10/06/1972 Crankshaft Bearing Insert Selection
750 #15 01/31/1975 Modified Throttle Valve and Cable Kit
750 #16 05/20/1970 Camshaft Holders and Caps
750 #18 06/13/1975 Drive Chain and Master Link Selection
750 #19 07/02/1970 Adjustment of Cam Chain Tensioner
750 #21 09/03/1971 Drive Chain Maintenance
750 #22 08/28/1970 After Sales Service: Modified Chain Cover and Chain Oiler Parts
750 #23 09/17/1971 Brake Pad Wear
750 #25 09/21/1971 Carburetor Adjustment, CB750K1
750 #26 12/23/1970 Front Brake Disc Mounting Bolts
750 #28 02/09/1971 Drive Chain Link Removal and Installation Tool for CB750K1
750 #29 Crankcase and Final Drive Bearing Replacement
750 #30 05/21/1971 Drive Chain Oiler Adjustment and Replacement
750 #31 08/28/1974 Connecting Rod Weight Selection and Size
750 #32 08/09/1971 Drive Chain Recall Notice
750 #33 11/03/1972 Wiring Harness and Breather Tube Routing, CB750K1 & K2
750 #34 05/04/1972 Disc Brake Caliper Noise: CB750 & CB750K1
750 #35 11/17/1972 New Molded Countour Oil Hose
750 #36 04/06/1973 Rear Brake Wear Indicator, CB750K3
750 #37 11/19/1973 Wheel Sprocket Diameter and Chain Pitch Compatibility
750 #38 11/26/1973 Muffler Warranty Extension
750 #39 02/01/1974 Modified Head Gasket Removal
750 #40 04/01/1974 Modified Shift Drums
750 #41 04/05/1974 Front Fork Oil Seal Change, CB750K1 & K2
750 #42 07/10/1975 Cylinder Head Gasket Oil Sealing
750 #43 01/10/1975 Battery Cable Extra Lead
750 #44 04/18/1975 CB750F License Plate Bracket Plug
750 #45 03/24/1976 Soft Mounting Cushions Improve Instrument Accuracy