83 Interceptor Restoration - Broken Camshaft???

So I got this bike as a non runner a while ago with the intention of restoration. Luckily for me it was garage kept for the past 12 year. I went through everything to get her running (the standards). Was happy to hear the bike run strong. I could hear a tapping/knocking from the front head. Check cams, upper good - the lower I found a broken oil tube, cracked and welded chain guide and some striped & broken bolts.

Ok, fixed and replace everything mentioned above and all I could see. Only to have it start right back up again, no apparent oil leaking. Run it up to temp on idle only. It was only when I gave it some throttle I heard a catastrophic bang. I hit the kill switch immediately and began my investigation. The oil leak was back and focused my energy on the front head. I wasn't going to start it again until I find what made the noise I heard.

I opened the valve cover on 3/4 to see all the work I had just done, come undone. Again, a broken oil tube, cam holder blown out of its seat about 1/4", and 4 broken bolts, 2 striped head bolts, 2 striped valve cover bolts and this - a broken cam

So my question(s) is what would cause this type of damage?
Is it possible that it was a loose/worn cam chain that caused this?
What about low oil pressure to engage cam chain tensioner? (should be ok, new oil/filter)
If the timing was out????

I honestly don't think it is a flaw or fault in the camshaft (despite popular opinion re: chocolate cams) Had checked/inspected it the first time I made previously stated repairs & they were within spec. Both looked good and worked. Yes there is a chance of this being the problem but something tells me its something else.

Like I said the PO had already welded the oiler at some point. Chime in with your thoughts, suggestions and prayers.

 

Damn! Never seen that before! I'd wonder if you have a plugged passage in those intake cam holders. If the oil pump relief valve didn't open, maybe you could have a problem like that. As revs climb, the pressure rises until the oil finds a way out. Just a theory, I don't have any real idea.

I'd have replaced all those repaired parts before running the motor. Brazed parts aren't usually a good sign, even if the repair was properly completed. Did you re-torque the cam holder bolts? If so, did they torque down properly? If the cam caps let go and popped off, all those bolts probably stripped out the head.

My guess would be that the cam snapped when it came off the seat from the valve springs forcing it up. The 'chocolate cam' reputation wasn't from cracking cams...it was from scoring on the cam, bearings and followers. I'm told it was from improperly aligned cams.

 

I have parts left from my original engine, might be able to help by replacing brazed pieces and broken cam.

 

Poor thing suffered, then failed. VFs not noted for durable engines, especially with high miles. :distrust:

You got bit in the arse by a twice-abandoned, old, tired VF like so many others hoping to revive an ancient dinosaur.

 

I feel your pain. I owned a 1984. It was a nightmare, but it never did anything like that.





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The general reactions are not giving me the warm & fuzzies, but I remain hopeful, lol. I too have never seen or heard of a motorcycle cam breaking like that. Correction: 2/4 front cycliders/head - (not 3/4, I think thats my Sabre order)

So I did check passage on cam holders. Oiler tubes was clear too. I'm not sure (haven't researched it yet) how to check the oil pump relief valve. I'd like to do that to eliminate it as a possible cause.

Desktop re: my post, I did replace welded parts when I found them, before running the motor. That's how I knew the monkeys were in there; and no, brazed parts internally is not a good sign. Everything was torqued to spec and in order as per service manual. Yes you are right, the bolts in the cam holder are broken off, had to drill out and two striped in lower block.

I had that thought too, the cam snapping as it came off/out, but that always leads me back to what made it come off/out? Valve springs really??? Is the a way to check for improperly aligned cams. Is that another way of saying timing?

Allyance, thanks. I appreciate the offer - I may hit you up another time in the future I sure, lol. I have a donor bike to work with, we'll see how it goes!!! Thanks to you too Squirrelman & Alaskan, at least I know I'm not alone.

Ok, good news. I think I've found the cause of the problem. But now that I think about it, it maybe just more damage. The further I look the more I see. So I pulled the front head/cylinders off and It appears to be a broken cam chain tensioner spring. I found part of it or should I say it fell off in my lap - I haven't located the rest of it, I suspect/hope its in the pan. That being said, does any one know how this spring is to go back - when I get one. Gonna pull it from the parts bike. The parts fiche & manual don't show a view of it attached well enough to see a correct install. I saw some major scaring inside the case from the chain, I guess as it flopped around inside.

 

That spring is internal to the tensioner. I'm not sure about what the correct part names are, but it connects a pin on the adjuster leg to the locking block.

If you look at the crescent-shaped adjuster leg, you'll see a riveted pin in the middle. That gets one end of the spring. The other end of the spring keeps the block tight up against the locking pushrod. I tried to take some pics of my spare V65 tensioners, but it's hard to see what's going on. Here's a pic from the top of the tensioner. You can barely see the black vinyl sleeve under the adjuster pushrod, the block is at the bottom:


Here's a picture from the underside of the tensioner. You can see the pin and the vinyl spring sleeve in the middle:


IMHO that chain is easily strong enough to crack a cam, once it's pulled out of the bearings. I'm not sure if those cams are cast or forged, but hard grades of steel are always brittle.

 

First let me say I don't know anything! Just a guess here. Look at the cam lobes, especially the short remaining side, not the side with the chain gear attached. Any damage here? My guess is something got caught at the lobe and caused that half to lock up. When the lobe got jammed it caused the cam to lift slightly until the power of the engine sheared the complete camshaft. The only way to shear a shaft like that is to hold one end solid and apply a lot of torque to the other side. Something caused that end of the cam to lock up! Not a lot of room for errant broken parts to float around without them getting jammed somewhere.

Again I'm only taking shots in the dark!

Yes, you get my prayers!

 

Wow, thanks Desktop, those pics are great. Exactly what I was looking for. I haven't pulled it from my parts bike yet 'cause I was trying to get a better view. Awesome it helps alot. Do you think the cam chain is still ok after this? Is there anyway ok knowing w/o pulling it out?

Maggot, I tend to agree w/ you re: it jammed on the short side first just before it snapped. Something cause the cam to lock-up. Looking at the wear damage, it's all on the left. So this in mind I think the tensioner spring was originally broken which was allowing the engine noise I could hear and the timing was off. Couple that with poorly lubed cam holders, striped out long cam chain holder bolts, increase engine vibration/throttle/rpm/load, cam lifted, chain skipped and BANG! Right, no room for floating parts, that means the spring end is in the pan right. I was able to hand crank the engine via stator in order to remove the head. No hanging or snagging to speak of.

Allyance, I will take you up on your parts offer. I'll PM you later to talk.

see video of it running the day I found the brazed parts, but before I replaced them, and coil to get it on all v4. Sounds pretty good, slight knock in the front
https://www.youtube.com/watch?v=9kHwRCciKJI

 

No prob, glad to be of any help whatsoever. I'm not sure if you could check the chain. It's an endless-loop chain, you'd need to split the cases to get it off the crank. Those Hy-Vo/silent plate-type timing chains rarely come with master links, although I have seen a few for sale in the aftermarket.

If you get a chance, I'd take a flashlight and verify that the lower chain guides are still intact and bolted into the block. One per chain - they're parts #11 & #13 on this diagram:
http://www.partzilla.com/parts/sear...983/VF750F+A/CAM+CHAIN+++TENSIONER/parts.html

 

It's a noble but losing battle, so scrap that engine and keep the bike parked until you find viable replacement.

Why spend alot of effort trying to rescue something that wants to give up? Hundreds of newer, better bikes are available that need far less maintenance. Not our responsibility to fix what was possibly flawed from the factory. Move on. In stark contrast, your resto on a VFR ( anything since '86) would be more rewarding both in ride and value. Gear-driven cams is the only V-4 way to go. An '86 VFR750F is displayed in the Barbor museum collection, but no VFs ! An informed indication of collectability with top-of-class design and AMA race- winning credentials.

:congratulatory:

 

:shame:

Thanks, Captain !! I'll do more research before posting in future.

 

LOL! Sorry... Just had to.
Cheers!

 

Oh man....that's purty good. Plus it's a 500! Isn't that your least favorite of the bunch squirrelman? But I do agree with you that this particular engine must have something very wrong with it. But it can be fixed, heck anything an be fixed.....except....a popped balloon. It is impossible to fix a popped balloon. So there. But is it worth it? I dunno...that's up to the owner to decide.


You know the first gens are considered by a lot of people to be the first true sport bike? (Yamaha fans will say it's the RZ350, but it's a 2 stroke so I dunno) How could the first modern sport bike not belong in a museum? I would argue that if they hadn't had the cam problems they would be VERY collectible and highly sought after today. It seems they are becoming increasingly collectible now despite the horrible cam eating reputation.

I own a 1977 KZ1000 and a 1984 VF700F, the differences between the two are staggering. The VF700 feels SO modern compared to the KZ. There is a 7 yr spread between my bikes but Kawasaki was still making the same KZ1000 (dressed up a little different) in 1983 when the Interceptor came out. The Interceptor must have been like something from another planet when it came out. I was only 4 in 1983 so I don't really remember first hand, but I would guess that was the reaction anyways.

I haven't ridden a 2015 Interceptor but I wonder if the 30+ year difference would feel as apparent as the 7 year difference between my KZ and VF???

 

I have to agree. The VF bikes were way ahead of their time. Styling wise they still hold up in my opinion. I have the fully faired Euro VF500 but I much prefer the US half faired version.

 

In this case i think it's clear that the cam snapped when the chain tensioner went bad, causing the cam to jump timing and a rising piston hit a descending valve.

 

Wow... I have a couple engines where valves met pistons and did that popcorn popper push vintage vacuum cleaner thing and didnt break a camshaft.... Something is fucked up.