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broken camshaft holder, leaking tachometer oil seal cb750 dohc

I would not be doing that at all, the only way to wash a head with water based product is bare head ONLY. You will find that in the real world your idea is heavily flawed. You cannot use minimal liquids as any soap on earth will corrode aluminum if left to dry up, why you have to flood the cleaned area once worked over. The popular engine cleaners like simple green and purple power never are found where I work on engines, they have ruined way too many parts.

I use fuel now because of the only good quality ethanol in it has, it allows the fuel to wash clean off with no afterfilm like straight gas leaves behind because the ethanol component mixes with water. I will kill as well to avoid at all costs trying to ever clean assembled parts, you are asking for problems when the cleaning medium does not 100% disappear, and valves in place as an action is begging to seize valves up once you run the engine.

Myself, if I were stuck with your issue the entire head would have to be disassembled to clean it right. Meaning all parts marked to go back in the right places. The slightest speck of hard detritus in a cam bearing and scar it up and head is then junk. Heads with that much mechanical complication inside them need to be treated just as if you were working on a human body and have cut inside to do the work. Meaning it cannot be too clean, meaning second after that any pre-lubing like oiled valves guides will be gone and very possible alien substances in oil galleries.

Having said all that, yours and do as you will................
 
If valve cover is BOLTED BACK UP, the idea might work but will depend on how much water you are throwing around there. Use high pressure air to blow things clean when done and do that immediately following the cleaning.

WD40? Highly overrated, I've seen what it reduces down to with time and it is not pretty at all. More like a gum than an oil. It has one specific use for me, clearing rotary file teeth when I port on aluminum. Used on things like locks, latches and such after a time it makes them WORSE, they begin to drag or stick heavily until you add more to only make it worse. Left in place as an engine starting lube is begging for seizure of parts.
 
Thank you amc49 as always! Will keep that in mind. The problems I face with this engine keeps piling up! Another thing I noticed when cleaning the head surface was this:

https://drive.google.com/open?id=1L8N8fuB8Yg5BKseDFgrErsiwDl-KcRuW

[url]https://drive.google.com/open?id=1LAuRtgfXmpRqdU1hQY9IkMl_jovm9r0j

Is that too bad? I can surely feel it with my fingers. Do I need to get the head faced? Will the gasket seal if I use it as is? Any way to fix it myself?

Also, lastly, is this "clean enough for the head surface?

https://drive.google.com/open?id=1LEWlxQblSqQrJWmbohBKrzCEu2YcZ2Jz
 
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You really should clean up the rough edges that are in the chamber. Have you checked the deck to see if it is warped?
 
The deck is not warped (had it checked at a machine shop). How do you suggest I get the chamber cleaned (don't have any power tools on hand)?
 
I for one would not do much there. The head gasket if it is one of the purely round ones at the bore can be laid over the damage in the proper place and anything inside the gasket steel ring is fine. That is flat quench area and sweeps quite a bit in pumping action, the DOHC if anything is sensitive to the ENDS of the combustion chamber rather than the front/rear sides and where most detonation comes from on that particular type chamber. The engine is low compression to begin with and that drops the need to get rid of sharp edges too. I know why he wants to smooth that off some and if a race piece I would be doing the same but keeping compression about the same is more important here to me as there is so little of it anyway and the DOHC tends to 'snuff out' more compression anyway as the engine speeds go up due to the whacky curves in the intake ports, it's why you can jack up spark advance and not get nearly the detonation other engines get into almost immediately.

The damage absolutely cannot get into or past the metal 'fire ring' in the gasket or that can be a leak at any dent going there to blow gasket out pretty quick. So lay out the gasket on top of the holes and center it up like it will run and look carefully at the damage locations, typically what is there will fall just inside of the gasket and be OK.

I might take a file and just barely work the biggest dent there, simply to remove what looks like a curl of material that will likely come loose in use, again, thinking only of the highs and not the lows. The highs are also what holds the metal curling from impacts that can vibrate and then the curl comes loose to run through the engine. Mostly harmless but with the odds of things can rarely damage something else like a ring when it happens to impact in ring land to then get stuffed deeper. One of the millions of things that can happen out of the blue when you are doing something at 5000-8000 times a minute.

Head looks clean but that is subject to looking at one over the net. You of course as the user must determine for yourself true clean, why we overemphasize it so much, with the understanding only half of what we says truly gets across. Obviously the cylinder block top must be just as clean.
 
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Okay. Great knowledge right here! Thank you. I have also read that its almost essential to change the base gasket once the head is taken off on these engines. How true/crucial is that? They say the base gasket wont seal right if not replaced.
 
If during any work the base of cylinder assembly came up off of 100% all the way down then the gasket will be loose and likely torn, it will then tend to leak. Careful work making sure the base gasket is never stressed can have one change the head gasket without having to do the base one. If you never yanked the one bolt that holds the cylinder down, the one in the front down low then the gasket may be OK, but the cylinder CAN be broken loose without yanking that bolt if the force is high enough.
 
So while taking the head off, I undid the head nuts half turn at a time at first and then gradually took them off in the pattern suggested by the manual and have not touched the bolt in the front bolt holding the liners. In your experience, is it worth going the extra step and replacing the base gasket while the head is off? Also fyi, I strongly believe that this engine has never been apart and so the gasket below is factory Honda (the bike is a barnfind which sat for 20 years). Would like to know what you think.
 
Okay so here's an update: Since I heard a lot of ppl saying that the base gasket might leak even though it was perfectly fine earlier, I decided to go the extra step and take the cylinder buckets off. After about 2hrs of trying with prying and hammering with a wooden block and managing to break a chip off of a cooling fin, I am really unable to get the bucket off.

What do I do now? Should I just get the head on and try to run the engine as is? Does the fact that the bucket not wanting to come loose mean that it would seal good? Although the chip that broke off from the fin is quite small, would it cause any problems?
 
Now you know why I leaned the other way. Many people destroy the cylinder block trying to get it off, they get stuck from water running down the studs to create whopping corrosion down in the bottom 1/2" of the holes and it glues the part down.

Still can't say whether bottom gasket is still good or not, you have jumped into the fire now. Taking cylinder off means having to refit rings back in without breaking them, another major action. The fin is an appearance thing only.
 
Jumped into the fire indeed! Okay, I guess it now makes sense for me to take the risk and not take the jugs off and assemble the engine as is and hope that nothing leaks. Btw, what exactly does the gasket seal? The manual says that the oil line runs externally from the crank case to the head and then returns from the head by falling into the cam chain cavity in the center. Correct?

Also, since this engine has been sitting for long, what other checks/things should I look for? The engine turns over smoothly and as said before, I just got a valve job and clearance done. Like always, thanks for the knowledge amc49. Enjoy the holidays!
 
Been a while after I jumped into the fire! The cylinder bucket has still not come out. Any tips on how I can do that? I feel stupid for having tried to remove this but now, having tried so, I am definitely in the fire and want to replace the gasket beneath and check ring end gaps too. Any suggestions/techniques will be helpful!

Also, I still can see the factory crosshatch pattern in the cylinders but there's also some light brown discoloration due to rust inside, should I re-hone the cylinders?
 
You don't hone if rings get reused but now that you are yanking cylinder it can be difficult for newbies to get the cylinder back on without damage to original rings. New rings hone the cylinder. Small spots can be touched up with #600 sandpaper.

I simply work on the cylinder until it comes off. WD40 put in the stud holes down low (in the fin holes where they open up around the studs) and around pistons can help but then the resulting mess has to clean out of the crankcases. Some people have had to resort to making up some sort of puller to pull the block off, I've never had to do that. FYI, the sticking point is the gasket itself and then once lifted enough to shear it the trash at bottom of the stud holes is mainly the issue. If engine is stuck then pistons become the major sticking point. Rings are junk in that case.
 
Hello. Been away for a bit but getting back to work now. I have gotten deep enough so will definitely take out the cylinders and measure piston ring end gaps etc. My question now is, given how deep into the engine I will be once the buckets come out, should I be inspecting/servicing anything else in the engine (the bike was sitting for a good 20-25 years)? Also, once done, whats a good way to flush the crank case? Thanks in advance!
 
You use clean shop towels or other to block the openings at top, you do NOT look for a chance to flush as there are so many trapping points you can easily blow up the new motor doing it. The DOHC has several oil orifices to block off oil channels almost completely except for a small pinhole to meter oil, solvents or soaps trapped in the even in residue will wreck havoc with your engine later when they come out or plug the orifice to not oil critical systems.

The ONLY way to get all clean with zero problems is engine apart as far as it can be and even then there are a couple spots that can still do it.

Timing chain tensioners are commonly junk if you have 40K miles in a hot climate, the rubber is cracking by then. You can't change the long chain unless crankcases are apart.
 
Speaking of the tensioner, I did notice that the rubber covering the spring has turned hard and begun to shred. Is the rubber crucial for the internals? Although I have not studied how necessary it might be in preventing internal contact between elements, I was considering using the tensioner springs without the rubber covering. Is that ok?
 
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