1982 CB750F valve check, questions

A

armourbl

Active Member
I just got this bike and did a valve check today. I want to get input from the experts if I can please.

First question is the marks on the cams were not aligned. Hopefully you can see in the pic. The exhaust side was off my a bit more than I would assume is acceptable. Does this indicate that I need a new cam chain? I will check the tensioner once it get everything back together. Bike has 23,000 miles.

Other question is my valve specs. I know I need to get all of the intakes back to .005, but is it worth it to do the same to the exhaust since they are at .004?

Thanks,

Ben
 

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Also is there any way to tell if I have the original cams or units from a 900?

Reason I ask is there is a set of cams in the box of spares that came with the bike. The guy I got it from got the box from the original owner when he bought it. So no way to ask on the history.

Ben
 
It looks like the cam is either out by a tooth or you have slotted cam sprockets in there and they need to be set properly. At 23K a hy-vo cam chain should still be OK.


Normally exhaust clearances are greater than intake, so you should probably do all the clearances while you are at it now.


Once you have the clearance measurements you can take out the cams, measure the shims and swap them around to get as many valves in spec as possible - then if you're lucky you'll only need to buy a shim or two.
 
I've only had a it a bit more than a week. I've put about 150 miles on it and it runs good. Just been going through it and correcting minor issues here and there.

Ben
 
I already have an assortment of shims that came with the bike. Just waiting on the bucket depressor so I can remove the existing shims and figure out what shim to put in. Hopefully I have enough of the right ones.

Ben
 
hillsy said:
It looks like the cam is either out by a tooth or you have slotted cam sprockets in there and they need to be set properly. At 23K a hy-vo cam chain should still be OK.


Normally exhaust clearances are greater than intake, so you should probably do all the clearances while you are at it now.


Once you have the clearance measurements you can take out the cams, measure the shims and swap them around to get as many valves in spec as possible - then if you're lucky you'll only need to buy a shim or two.
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What are slotted cam sprockets?

Ben
 
The holes where the bolts go are elongated or "slotted" to allow for valve timing adjustment. Also referred to as "dialling in" the cams....


sprocket.jpg
 
If it ran good and you don't know what a slotted cam sprocket is then why are you attempting engine work?

Funnsies?

You do know that by tightening the clearances that you have suggested, it will shorten the period of time need between adjustments, right?

You realize that shims only come in certain sizes, right?
 
There isn't a single clearance shown there that needs adjustment. (if You measured correctly) You are wasting your time and ours. Verify cam timing, put it back together and ride It. In fact just put it back together and ride it because by your own admission it runs good already. Now you wanna mess with stuff? WHY?

He probably has a nonstock set of cams in there and with the level of knowledge you have displayed thus far it will end up with a motor in pieces that never runs again.

Anyone telling you to adjust the clearances from what you have is ignorant to what is going on here and needs to be asking more questions.
 
DohcBikes said:
There isn't a single clearance shown there that needs adjustment. (if You measured correctly) You are wasting your time and ours. Verify cam timing, put it back together and ride It. In fact just put it back together and ride it because by your own admission it runs good already. Now you wanna mess with stuff? WHY?

He probably has a nonstock set of cams in there and with the level of knowledge you have displayed thus far it will end up with a motor in pieces that never runs again.

Anyone telling you to adjust the clearances from what you have is ignorant to what is going on here and needs to be asking more questions.
Click to expand...


Well, you can only go on what information is provided, but seeing the acceptable lash is .004-.006.....and assuming the measurements given are correct...then there's a few intake valves that are too loose and pretty much all of the exhaust valves are marginally tight.


Maybe you should stick to posting crap 90's music videos in that other thread of yours.
 
In addition, my advice is to leave a good running engine alone.

All day buddy.

Your advice is to tighten the clearance on his intakes without know anything about how the previous builder set it up. For all we know it needs more clearance than stock due to aftermarket components.

You are showing your ignorance once again by even mentioning somebody's taste in music on an engine help thread.
 
I'd go with what dohc says. Clearances inevitably tightens with wear, and this was probably set not long ago, since clearances grow a bit first, before it starts bedding in. Different cam profiles require different timing, hence one cam being off a bit. Camchain play is more important.
Plus tons of people break engines by pure ignorance when doing regular service.
 
^^^YEP.

I may be a little crass but I'm trying to save you an unnecessary headache man.

From your other thread:

"You don't even know what cams you have. Many high performance cams require more clearance.

Valves should be adjusted to the loose end of the spec because they tighten over time. Possibly your cam requires a bit more clearance than stock...how do you know? What you do know is that it was running good before you started 'fixing' It. If it ain't broke and you don't know what a slotted cam sprocket is leave the damn thing alone.

Not a single shim needs messed with anyone saying otherwise is wrong.

Was it ticking wildly? Was it bogging? was it running out of breathe at high rpm? NO. Know how I know? Cuz you said it was running fine.

You're gonna put too thick of shims in and next thing you know you'll be asking why you lost power.

You're messing with stuff just to mess with It. Go for it but don't be surprised by an I told ya so when it runs like poop."
 
I appreciate all of the answers, and I'm doing my best not to take offense. It is a forum, and what good would it be if people can't ask questions and find answers.

My post was hear from and learn from the experience of others related to valve clearance. I'm not an idiot who just opens a motor for fun. Heck, I actually have resolved many issues with this bike by opening things up and checking status. Sure, I didn't know what you meant by a slotted cam gear, but it did dawn on me later. Just hadn't heard the term before. Yes I know about shim sizes, and realize that in some cases I may have to compromise on the desired valve clearance.

This isn't my first or my last motorcycle, and I do all of my own work on my bikes. I know my way around the garage, but I'm still learning and expect that I will be for a long time still.

My opinion on the valve clearance is that all of the exhausts are on the tight side and should be adjusted. As far as the intakes go, the ones that are reading .007 or greater should also be adjusted at a minimum.

What I don't know and haven't come across any information about is how quickly valves clearances on this bike change. To me, that might play into the thought process of setting them on the loose side.

ben
 
What makes you think the exhausts are tight? Some random internet spec? Been a while since I've worked on one but I think the Honda manual says .002" and even if you are going by the ".005" for all of it" then you are still close enough to spec to LEAVE IT ALONE.
 
Already told you twice that since you don't know what cam you have you don't know the clearance you need. datadavid explained further that They were more than likely adjusted recently for the cam swap.

Your engine is not stock.

Leave em alone and check them next year this time.
 
There is some good advice here. Most valve trains get noisy if they are have excessive clearance (some are pretty noisy with correct clearance). Too tight you will lose power and ultimately do damage. Once close to the correct clearance (means that there is at least a bit under any circumstances) there is really not much to be gained by getting more precise adjustment. It takes a rather a lot of excessive clearance before the valve lift and duration and performance (unless you are racing) are significantly impacted and at that point many engines will have so much noise you will think something is broken inside. Only a bit tight when cold or warm may be significantly too tight when really hot causing the valve to not seal and bad things will not be far behind. Erring on the loose side of the suggested clearance range is usually the best plan. Considering your bike runs well, and all your measured clearances are so uniform and evidently within spec (don't know and didn't look it up myself) I think I would leave it alone. If you started with the specs way out of range and re-shimmed it to the clearance you have now, you likely would consider it a job well done!
 
jpmobius said:
Erring on the loose side of the suggested clearance range is usually the best plan. I think I would leave it alone. Consider it a job well done!
Click to expand...
This
 
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