My "new" 83 vf750f making noises....maybe won lobes, maybe something else?

B

Beeton

New Member
Picked up an 83 as noted for $75. Not expecting a miracle but just something I was interested in to replace my 500. This bike ran well then started to run rough (as per previous owner) then sat for 2 years. So, front tire flat (valve torn), rear calipers stuck and we rolled it slowly onto my trailer.
My son and I squirted some oil into the cylinders, drained and then sprayed out the carbs, drained and replaced gas and added some Sea Foam, cleaned plugs and then cranked. Apart from a sticking starter switch, fired right up. There was lots of noise from the rear bank and that increased with rpm.
We opened the cover, regapped at .005 as per the Clymer manual (they did seem a bit tight), made sure everything had oil and tried again. Still, that noise that did sound like loud valve chatter but not quite.
The rear of the #1 lobe had scoring but the contact end seemed fine as did the #3.
Reading through forums, I noticed a .006 gap revision had been issued from Honda so I regapped at .006 (or maybe .0065) and tried again. Still that noise.
Probably worn lobes but maybe a tensioner issue?????
I have attached a link to a youtube video I posted and that noise is evident. During the middle, the camera is pointed away from the bike so that the mike is pointing at the sounds.
Any tips would be appreciated.

 
Ouch. That's loud. It does sound like a valve. Almost sounds like a valve hitting a piston, but you would have found very large clearance if that was the case.

That model had a reputation for having chocolate cams ie they just disappeared and there was a factory fix of some sort.

My first inclination would be to drop the motor and strip it to see what's going on, but before you do that, do a compression test on all 4 and then a leakdown test and see if that reveals anything. I would also check all the engine mounting bolts. Sometimes a noise like that comes from the motor moving in its mounts or an exhaust pipe hitting the frame.

Good price as long as it came with a title. If the cams are worn, Megacycle offer several grinds on your cores along with hard welded rocker arms. Not cheap but should be bulletproof. Lots of used pistons on ebay if that's the issue, but it was a 2 or 3 year model and may cost more than it's worth to fix. Don't give up yet.
 
Teaser. If valve was interference, wouldn't that be too tight clearance? I may not understand the mechanics at work
 
I can't watch the video at work, some valve noise is normal on some Hondas but IDK on the VF if and how much is normal. My old CM450T sounded like a sewing machine at idle and lower RPMS when cold, would get quieter after warm but you could always hear some. It was normal and if you set the valves top make them quiet you would risk damage to the engine/pistons. Check what teaser said that all the mounting bolts and exhaust bolts are tight. Someone else will hopefully chime in on how much of the noise is normal on these.
 
Did you adjust the valves using 2 feeler guages so you adjusted both adjusters on the same rocker at the same time? There was an update from Honda on the correct procedure since the rocker would cock a little on the shaft and add that clearance to the feeler gauge if you only used one. You could not get an accurate setting with only one. >006 seems a bit large for most Hondas of that era, but if the FSM sayas thats what it is, I guess it is ok. I would have expected more in the .004 - .004" range.
Honda also had a special tool that pulled the cam up into its cap that allowed the clearance to be set.
 
Turns out, the left-rear follower was really cupped so no amount of adjusting would help. Ordered a used head and looks much better. Now debating changing head vs changing just cam and follower (but that would require an engine removal.... lots of work). As I can't be sure the old head doesn't have a damaged valve tip, and this one looks perfect, better to change the head I think. Gaskets are on the way.
 
The worst part of engine work on those bikes is getting the carbs on and off. Pulling the engine is pretty easy after that.
 
The tensioner had various issues and would stop working.
My least favourite Honda of all time as I spent way too long at Suzuki dealer fixing the ones Honda shop across the road wouldn't do(minimum of one a week for over 2 years, sometimes 3 or 4)
Couple of relatively quick fixes.
1- remove the damper rubber from tensioner spring, it was too long on early models and went hard on later ones.
2- knock out pivot and rotate shaft 180 degrees so worn portion isn't on the lock piece.
You can do this without pulling heads. Just remove cams.
gear drive - early ones total disaster. Bearings would break up and only fix was new very expensive parts.
If you got real unlucky it could break a tooth then cheapest fix was a used motor
Carb removal and fitting isn't too bad if you completely remove the clamp bands, spray WD40 around everything to remove and engine oil when re-fitting.
A 4ft length of 2x4 is also very useful
The Honda tool is just a clamp to hold cam into top bearing, needle nose vice grips work about as well
 
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