• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

broken camshaft holder, leaking tachometer oil seal cb750 dohc

Rubber over the spring is not that big a deal for a while, eventually the spring can break though, the rubber is a vibration damper to keep spring from rattling to break. More important is flexing the tensioner and watching for fine cracking in the rubber there, it comes off in pieces and the actual steel parts then break tensioner as there is not much steel under the rubber in places.
 
Last edited:
Hello! Posting after quite some time. After a lot of hard work and patience I have managed to take the cylinders off. It felt really good to be taking the cylinders off but to my dismay, the connecting rods are in really bad shape. They are rusted an unexpected amount. I think I will have to opt for a complete rebuild but just wanted to run this through you so that I do not overlook any thing here. I am not that knowledgeable when it comes to con-rods and replacing them, so advice will be much appreciated.

That's what they look like:
https://drive.google.com/open?id=1dEpW5gLadWuXsgaDAqyjwKLqjafeWvNW
https://drive.google.com/open?id=1dHcFWbJohcyEa_dmL6B0CyhPpAT8ktzl
https://drive.google.com/open?id=1d8kk0Bef-xjjISUzNoVXsz4lxTEZ0NYS
 
Engine comes apart to fix it. The rods get glassbeaded then you look at the clean part for pitting holes that later will snap the rod in half.
 
Hello, posting after some time again! Since having taken the cylinders off, i have worked my way through till splitting the cases apart. However when I tried to, I realized that the alternator rotor had to come off to split the cases. Now taking the rotor off has been a complete pain in the a$$. The rotor bolt came off great with an impact gun. I know that taking the rotor off needs a puller but I was told that we could use the rear axle too. So using the axle as a puller, I have tightened things down using an my impact wrench and have given the axle quite a few wacks with my hammer. The rotor still doesn't want to come off. Any tips on taking that out? Can it be that stuck (most youtube vids show it coming off pretty easy)? Also, am I missing something?
 
The axle works fine but you have to make sure before every hammer hit it gets screwed back tight to positively lodge against the crank material. A whack or two lets the softer axle end impress enough to back away from hammer action metal reshaping to let a space enter and then the hammer whacks only stress the rotor threads with nothing going into the crank end itself. Axle having even .005" clearance and the impact won't touch it. MUST be solid against the crank to produce enough interference stress to pop it loose.

Never seen one that was constantly adjusted up after every whack take more than 3 whacks to pop it off. If rusted like engine lower end it may be stuck on to stay. More force needed but don't be surprised if crank damage ensues. Do NOT use a small hammer like for construction, bigger one to take inertia effect better, is best there, I never use a small one. And solid metal, no plastic hammer. I use baby sledge and then I hold back on the force, let the weight do the work.

Screw some bolts back in to positively hold case halves together, you will damage all mains not doing so, the looseness lets the crank deflect in the holes with loose cases. Now you are battering your mains.

Luck.
 
That's some great advice! I had indeed already tightened all the lower crank case bolts before starting on the rotor. Talking about the rust, the external body of the rotor is not rusted at all so i am not sure if the joint is jammed by rust (it could be, but then it must be internal).

amc49 said:
Axle having even .005" clearance and the impact won't touch it. MUST be solid against the crank to produce enough interference stress to pop it loose.
you mean to say the clearance between the end of the axle and the crank? If so, is there a way to find out? I actually approximated the depth of the hole in the rotor and the number of threads left on the axle to figure if the axle was all the way in. By my logic, it seems like its in there.

A friend of mine suggested using a puller that he designed wherein a female piece with external threads to thread into the rotor and internal threads to allow a male bolt to thread into. The male would then thread in to butt up against the crank, hopefully getting the rotor out. I am going to get it made but just wanted to throw the idea out there. Any issues that this could cause?

And thank you so much amc49!
 
If either thread set of your puller is not long enough they will peel threads off, the part needs to be hardened too. Seen cranks ruined before when the threads in the end came off. The axle is actually the better removal tool.

You screw the axle in to positively hit solid and even torque it up a bit to guarantee in ALL the way SOLID, and repeat the same every time you whack the hammer. You will find that every hammer hit loosens the interference to do nothing thus killing rotor threads. The axle MUST be tight before every hit.

Hold the axle as a handle while whacking, when rotor pops loose it will actually jump away from the crank quite a bit. The normal rotor install torque there is around 75 ft.lbs. because there is no keyway there. They are really on there.
 
I got the tool I mentioned machined and tried using it. It seems to be doing whats intended but the rotor refuses to come off. As you mentioned, I am led into thinking that this will probably need more force than the tool or axle can deliver. In that case, do you think a 3-jaw or 2-jaw puller might be able to get the job done here? Saw a couple of videos on youtube where the guy takes a rusted rotor out using one.
 
You absolutely cannot use a jaw type puller on that rotor. Do it and see why, the rotor will split in half. And ultimately apply no more force than the axle did. The axle is actually stronger.

You CANNOT 'pull' that rotor, not the way it works. What you actually are doing is setting up enough interference so that the hammer whack is what knocks the part loose, not any pulling you can possibly imagine there. If you insist on 'pulling' then the puller will destroy trying to do it.
 
Okay. I have been trying and trying and trying but no success. The more time I spend on it the more badly stuck it feels. Another problem i face is that, since the engine is on my bench and out of the bike, tightening the puller/axle becomes a hassle (any advice on that? I have used the drive chain and a screwdriver to jam the drive sprocket). Anyways, I am looking for a solution desperately, given that its stuck that bad and that I do not want to damage the crank in any way, what other option do we have? I am really grateful for all the help and sorry for the multitude of questions :D
 
Advice? DON'T use a jawed puller. Past that I have had no trouble knocking like 50 of them loose. Most were engines out of frame.

You absolutely cannot avoid whacking against the crank, lodging the tip of the tool against it is what pops rotor loose. If you aren't impacting crank end it does NOT come loose. Up to you to do it in a fashion that does no damage. If you have been running the tool in to just short of touching the crank you may well have super swedged the rotor on to never come off. Cannot help you with that as I never have been there. If faced with the issue I would be looking for another engine.

As I have said, or tried to, you don't 'pull' those, the actual pulling process does not apply enough force. The only way you get them off is by a sudden force directed hit to pop the rotor loose from the crank, you must strike the crank at the nose to do that. Why the puller MUST BE DEAD SOLID FORCED into the crank before striking it. If you have already struck the rotor enough to put it on tighter you may have scrap parts there.
 
If you absolutely must you can use a pipe wrench LIGHTLY on the INNER half of the rotor that runs next to cases to lock rotor in place enough to tighten axle more. DO NOT USE THE OUTER HALF, INSTANT DESTRUCTION of rotor doing so!!!!! The pipe wrench (needs toi be a newer one with sharp teeth or waste of time) will cut little trenches in the soft cast iron of the rotor OD and you must trim them flat with a file so the gouges do not contact your stator while engine is running. Apply the wrench to the bigger part of the tangs where they join at the back co-molded ring, if you grab closer to the middle of rotor you will crack a tang off and rotor is then scrap.

You see how easy it is to break parts when you step 'out of the envelope', why I didn't want to mention it.
 
Hello amc49 and others here. So after a lot of struggle, I did manage to take the rotor out (got the hardened steel puller and it worked!). You were right! However, the two piece puller I had mentioned earlier did a litter damage to my crank threads (I think it damaged one thread). The question is, would chasing back the threads deal with the issue. Its not major damage just one thread that's damaged (as far as I can see).

Another one, since the rotor came out, I got to split the cases and take a look inside. This is how my main journals and shells look:
https://drive.google.com/file/d/1Q0VDcJSoKXrHSKnyNYM4F_UevAKJRdYH/view?usp=sharing
https://drive.google.com/file/d/1QrI6of6Uk4DwBa_SNYqm2A_nlYOq8OQL/view?usp=sharing
https://drive.google.com/file/d/12GKPt2B5K5NBJbhynVUncPTHC0IXWrSc/view?usp=sharing
https://drive.google.com/file/d/1NO2rFtR11EyBsLIsiqK2pKhOQAXlqLx4/view?usp=sharing
https://drive.google.com/file/d/1sfFm6uguzVz7lEZ2Hg-QlgVCRDPbJ_52/view?usp=sharing

Is that water damage? Should I look into anything else specifically? I will be replacing all the shell bearings (following the manual) but just wanted to ask if, given the current state of the engine, would you suggest replacing anything else (other than seals, shells etc etc.)
 
amc49 needed your opinion on some damage on my crankshaft. I feel really stupid saying it out loud but, back when I was trying to take my alternator rotor bolt off, in order to try to keep the engine from spinning I had my friend hold the advancer spacer hex while I tried to take off the rotor bolt. Long story short, we ended shearing off the advancer pin causing damage to the crank. Here are some images:

https://drive.google.com/file/d/1-FUQBeHAAoG0X2AtYQ6yzHo0jvompJw9/view?usp=sharing
https://drive.google.com/file/d/1-CiT_W2hYal6wVJPCB1EkHBqwIp_z8AE/view?usp=sharing
https://drive.google.com/file/d/1-9gvtOzQwtVsBVW5MxFoI9nJLOWdC8zu/view?usp=sharing
https://drive.google.com/file/d/1-3r6XY8gHk8hv3G0zeUOUwNhFn4xoxIo/view?usp=sharing

What do you think? Its just the front of 1 spline that's damaged. The splines on starter clutch are fine.
 
Still useable but I'd file the bump there back flat to match the end of shaft the rest of the way around. To allow the advance unit to settle back fully in place. The advance unit may even be useable too if you haven't broken the pin off. Or even if you have if you are careful enough. You'll need to recheck timing.
 
Thanks! I am gonna file the bump back and do what you said. But yeah, i did break the pin off. What do you mean by "if you are careful enough"? Do you think it would be okay to tig weld and shape a pin behind the advancer to reuse it? Also, I am worried that the depth of the damage might cause the pin to slide off when running. Do you think something like JB weld or other metal putty to fill-up the indentation be a viable option?
 
Why? JB weld there is a mistake, the hot oil will have it chipping off in minutes. Heat removes it.

I am continually amazed at how many incompetent ways people think epoxy will work. Not a judgement against you at all of course, it's just that epoxy will not work like that and wondering why people think it might. This rant comes from the hundreds of times I sold the stuff while in parts after warning customers what they thought was was NOT and then later they came back to admit it did not work. Epoxy is wonderful stuff and I can use it to be almost indestructible but the rules to do so are VERY tight and do not brook breaking them at all.

Spray the crank hole for the advancer bolt with something that degreases the hole ONE HUNDRED PERCENT, 98 will not do. The hole MUST be BONE DRY and end of bolt as well. Trim flat the face of crank end and leave any dents that are LOW ones ALONE, they provide BITE. All you remove is the HIGHS. Mark things up in such a way you can tell if the advancer moves when tightened, it must not. Use a torque wrench and go past the torque number when tightening the center bolt and make sure while doing it the advancer absolutely does NOT move while tightening, use the bigger nut to hold the advancer in position. Don't go crazy or you will break the center bolt but it can be overtightened somewhat. The bolt needs to be loctited before doing that and why you degreased the hole and bolt. The overtighten sinks the advancer deeper into the lows left by damage and they in effect make a pin unnecessary.

People break or bend those pins all day long being sloppy in assembly. It can be off a little and you simply check and retime the timing plate to get back right. The overtighten then keeps it in place. Honda themselves had trouble with them moving and later ones got the loctite on the assembly line and you know it if you remove that bolt, they are almost impossible to get loose.

Now you know what 'careful enough' means.
 
Man that is some great advice! I really really am grateful to have access to someone like you that takes time to help novices like myself. Thank you amc49! One question though, I even sheared off the tabs that hold the lock nut/washer that you suggest holding on to while tightening the advancer bolt. Could I still do it holding it with my hand, slowly tightening it? Or holding the advancer back plate itself?
 
In any fashion that gets the part tight while still being pretty close to the original location of pin/slot. Provided you haven't messed up the advance unit swing to have it come apart. Holding the advance plate may break that depending on which way it swings, it is only small pinned like the parts you have already broken. You are already well on the way to completing a real butcher job there, there being limits to it before you scrap parts and maybe engine. You definitely need to learn when to stop to think rather than break.

Nothing personal intended there at all but it is what it is. I fix single messups all day long but multiples one on top of the other is junk status and the bikes generally display that by turning into such in short order. I fear greatly for you when you hit rods and crank. But then I may be totally full of crap.

Wouldn't be the first time.
 
Back
Top