Honda Twins banner

1 - 20 of 81 Posts

·
Registered
Joined
·
38 Posts
Discussion Starter · #1 ·
Hi all,

Here's the bike in question (with tank off):
IMG_0746.jpg

I posted a question here: https://www.hondatwins.net/forums/5...66-cb500t-running-1-cylinder-valve-issue.html

Long story short somethings up with my left intake valve and I have to take the engine off and dig into the head.

I started by removing the fuel tank, muffler, disconnecting all the various electrical components and was attempting to remove the cover over the chain on the engine when I noticed that a previous owner had done something unorthodox - replaced a philips screw with a hex (not allen key):

IMG_0748.jpg IMG_0747.jpg

Try as a might, I can't seem to get my wrenchs around the groove. And so for the first (of probably many) time I turn to the experts here: How do I get that bolt off?

Thanks!
 

·
Registered
Joined
·
4,458 Posts
I would take a dremel to the head of the bolt and make a small trench deep enough for a flat head screw driver to grab. Then use an impact hammer with the flat head bit to loosen it.
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #4 · (Edited)
Worked great! Got the engine out and the head off
! IMG_0771.jpg IMG_0772.jpg

I'm not exactly sure what I'm looking for - what do you guys think? Note that the left cylinder has a bit of oil and stuff where as the right cylinder is dry (the left intake valve was the source of the problem to begin with).
 

Attachments

·
Registered
Joined
·
13,085 Posts
Compare the look of the intake valves as they sit on their seats. You can see the edge of the wetter intake valve, near the outer edge of the combustion chamber, is raised up a little... that valve is bent. And there's some serious cam chain wear on the metal of the tensioner roller arm as well
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #6 ·
Thanks! I imagine I have to buy a new valve? Anything else? Should I take out the other cam (only took out the intake cam)? I'm going to measure the cylinder to make sure it's within spec, anything else I should check?
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #7 ·
Okay so I'm still trying to get the valve out - I think I've removed everything (maybe not?) and I'm not sure what I need to do to physically remove the valve. IMG_0775.jpg
 

·
Registered
Joined
·
6,495 Posts
Okay so I'm still trying to get the valve out - I think I've removed everything (maybe not?) and I'm not sure what I need to do to physically remove the valve. View attachment 267646

You'll just have to tap it out carefully with a punch, and hope you don't screw up the valve guide. I'd have a machinist check all the guides while it's apart - they're a relatively cheap fix.
 

·
Registered
Joined
·
170 Posts
Is the suspected bent valve the stuck valve? My valves came out easily on my rebuild, so I’m guessing this going to be something you’ll need to fix. I didn’t replace mine b/c they seemed okay, though in hindsight I wish i had while I was there. Would love to hear what you end up doing, if you get new valve guides pressed in/honed, what that costs, etc.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #10 ·
Will do - should I take all the valves out? I haven't even really touched the exhaust side (cam is still in).
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #11 ·
Is the suspected bent valve the stuck valve? My valves came out easily on my rebuild, so I’m guessing this going to be something you’ll need to fix. I didn’t replace mine b/c they seemed okay, though in hindsight I wish i had while I was there. Would love to hear what you end up doing, if you get new valve guides pressed in/honed, what that costs, etc.


Sent from my iPhone using Tapatalk
Yes - the stuck valve is the suspected bent valve.
 

·
Registered
Joined
·
7 Posts
If you rotate the valve is it obviously bent? if so it is scrap, cut it off with a Dremel as close to the valve guide as possible, dress off any burrs and tap it out. Otherwise if it's seriously bent you may wreck the valve guide if you're not careful. The guides are iron/steel so they will stand a bit of abuse. Yes, you should remove all the valves, it's a minor job compared to how far you've gone already.
 

·
Registered
Joined
·
170 Posts
I read somewhere recently on this forum that there is a guy here that will do a valve guide job for you for a fair price if you mail him your cylinder head. Keep that move in your back pocket.

I believe that if you replace 1 of the valves, you have to hone the guides or something like that. Maybe someone else can chime in on this, or you can read about it elsewhere.

Anyway, Hopefully you won’t need to replace more than just the single valve, but even if you don’t replace the other valves, I’m pretty sure it’s best practice to lap all the valves fresh. It’s not too hard if you clean up the valve heads/divots beforehand (eeeeek...I used a wire wheel...not the recommended tool of choice on this forum).

Phil


Sent from my iPhone using Tapatalk
 
  • Like
Reactions: TOOLS1

·
Registered
Joined
·
13,085 Posts
^^^yes to both above, if the valve is bent badly enough, forcing it through the guide could damage the guide. You want to avoid having to replace the guide if possible although member Tools can do it for you if necessary. Yes, to lapping in all of the valves while you're there to refresh the valve's seal on the valve seat (but the existing guides in good condition do not need to be honed, only a newly replaced guide), the 450 head is one of the easiest there is to remove and reinstall the valves. It's rare to have a valve bent above the guide, generally the bend happens from hitting the piston so normally the bend is below the guide and has no affect on removal. Yours is one of the more unusual situations to come along in a while... and I'd really like to understand how it happened myself
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #15 ·
I dropped the head off at a local auto machine shop to see if they can get the valve out - I couldn't move the thing in any direction as it was really jammed. I've ordered a new valve and valve guide and removed the rest (though the exhaust valves were a bit harder to remove). The machine shop said they'd get back to me in a day or 2 to see if they can help and if they suggest ordering more parts.
 

·
Registered
Joined
·
13,085 Posts
Hopefully this machine shop has some level of motorcycle head knowledge... they're a bit more precise than car heads (at least American engines, anyway)
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #17 ·
Hi guys,

Update. I've got my head back from the shop - they removed the bent valve but said the guide was still good. I got them to lap/cut the valves (ordered a new one to replace the bent valve).

Upon re-assembling the engine I've run into a snag.

I'm trying to put the cams on their timing marks at LT and then putting the master link on the new cam chain. The intake one is pretty close:
IMG_0794.jpg
but cannot freely (it freely moves but meets resistance at the place in the photo) move it to the timing mark. The exhaust cam mark is pretty much on the opposite side
IMG_0793.jpg .
In order to rotate the exhaust cam 360 degrees (both cams are like this) I am met with a lot of resistance (as I'm opening the valves). I am made to understand that at LT the exhaust valves are partly open. How do I get the valves open for the purposes of getting the timing? Thanks for all the help so far, I feel like I'm pretty close!
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #18 ·
Update: I got the exhaust cam in the right place and now just going to move the intake cam into place and I should be good to go!
 

·
Registered
Joined
·
13,085 Posts
Update: I got the exhaust cam in the right place and now just going to move the intake cam into place and I should be good to go!
I saw this right before going to bed, and it was too late last night to take the time to tell you that you set the exhaust cam position first, then thread the cam chain across to the intake side where you connect it after setting the intake cam position. By now you know the reason is the exhaust cam will sit in position while the intake cam is just starting to open one valve, causing it to spring back - so you have to hold the intake cam in its spot and slip the chain on the sprocket, then insert the master link. It can be a challenge, but once you do it a couple of times you get used to the procedure. Do you have something to stake the master link after putting the side plate on?
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #20 ·
Thanks Tom - I've not sure what would be a useful stake for the master link - maybe I have something sitting around?
 
1 - 20 of 81 Posts
Top