Issue in valve train

Blue750 · Aug 5, 2018

Hi,

Something broke today in my 750s valve train. I took the bike out, tickled the carbs, primed the engine with a kick and heard something break or hit within the engine. Further kicking over it went through freely with no other noises. So I decided to start it. Which it did with a single kick and a horrible tappet noise.

Drained sump; no particles. Checked compression; both sides give strong resistance to kickstart.

Checked rockers and found right side exhaust valve has 1/4" free play and push rod is loose. It's almost like the pushrod broke or dislocated on the bottom and dropped further somehow.

I guess the head needs to come off which is a first for me. Anybody knows what type of fault I may be looking at?

Thanks and regards

lazyeye6 · Aug 5, 2018

Sounds like the bottom cup end of the pushrod has separated from the pushrod. Yes, the head must come off which
is tricky and awkward the first time. If not the pushrod it could be a problem with the tappet in which case the
barrels must come off too.

kommando · Aug 5, 2018

Other issue to check if the pushrod is ok is the cam follower stellite pad which can drop off and is 1/4" thick.

lcrken · Aug 5, 2018

I'd vote for the pad dropping off the lifter. I've had that happen, as have others, but I don't recall ever hearing about a pushrod cup separating from the tube. Definitely time to pull the head, and most likely a full teardown. When it happened to me, it trashed the cam and put a lot of dings in the rods while bouncing around in the bottom end.

Ken

oldmikew · Aug 5, 2018

I suspect Kommando and Ken are right but before you get the spanners out have a lock at the tappet adusters is the offending suspect much higher than the others ? If so it could if you are lucky simply be that when the head was last lifted the push rod was located on the side of the cam follower rather than in the machined cup .. It can be done and will run for miles like this. My advice would be to see if the pushrod will locate and the tappet adjust so it protrudes roughly the same as that on the opposite rocker.. Then i would take the plugs out and gently push on the KS by hand If eveything opens and closes properly then you are probably in the clear. But be very gentle when you do this donot use force just in case it actually is the foot of the pad that has dropped off.

SteveA · Aug 5, 2018

Something that happened to me once....I had a small set screw fall into a bellmouth....

It went to the valve, the hex head stopped it falling right in but it held the inlet valve open! Pushrod cup fell out of engagement with the rocker arm ball, engine continued to run on one cylinder. I decided to take it home and inspect there so the clue for me was that when I put the bike on the trailer and shook it to make sure the tie downs were secure....the loose push rod rattled inside the motor!

Your 'strong compression' could be something else if an open valve touches the piston. Do check the valves are properly closed.

Forgive me on this, could be a complet red herring, but you don't say you used a compression guage or what audio accompanies the 'strong compression'. Is it still 'sucking and squeezing?

But.....I also had a stellite foot fall off of a follower and I would really go with that as the most likely issue.

Could be said that since you knew something was amiss, starting it up wasn't the best action, but here you are, and it is easy for me to be a smartarse at this point, sorry.

Blue750 · Aug 6, 2018

Thank you all for replying. The engine turns freely. It's not just 'sucking and squeezing' but holding well against the kickstart.

It will take me some time to get the head off. Will come back with the results.

Blue750 · Aug 7, 2018

Managed to get the head off today. Pushrods are ok and no valves have touched. One ex valve guide is leaking badly. Inlet guides are questionable as well. Bores look glazed and scored; although I'm no expert on this. Engine supposedly had a rebore and new pistons 5k miles ago.

Right now my spirits are down as I wanted to at least ride through summer. Didn't have the energy to take barrel off. Will report back when I get a look at the followers and cam. Also going to post pictures over the coming days as it looks like I need lots of consulting.

rvich · Aug 7, 2018

Look at the bright side. You get to spend your summer becoming a better mechanic. That's a skill that will last you a lot longer than the bugs in your teeth from riding!

Blue750 · Aug 8, 2018

Took the barrel off a few minutes ago. It's an ugly sight:
- Part? of the stellite broken off from the right side exhaust lifter
- Broken parts on the lower lifter guides of the barrel
- Bits jammed into the case in front of the cam
- Cam scored
- The top rings on both pistons came fell off as multiple pieces
- ...

Images to follow.

cliffa · Aug 8, 2018

Hi Blue750,
sorry to hear this. If I can be of any help let me know. (I'm in Wädenswil).

Cheers,

cliffa.

Atlas Commando · Aug 9, 2018

Bummer! Sounds like you'll be splitting the engine cases to set things right. If you haven't done this before may I suggest taking plenty of pictures and get a load of the ziploc bags you can easily write on to organize parts. I wouldn't go any further until I had enough time and cash to see it through. Nothing worse than a project with huge time gaps that allow small parts to hyper-jump into another dimension. Oh, most important.... hit the search engine here at every step of the way. This crew is well experienced and helpful!!

grandpaul · Aug 9, 2018

YEOWCH!

I can't really see how broken rings and the rogue cam follower face could be related...

Sorry, dude.

Blue750 · Dec 29, 2018

Have removed the engine from the bike and split the cases today. You may remember, I had lost a stellite pad on one of the cam followers.

Broken follower with damage on barrel/tunnels

Pieces of stellite that came out of the case

Pieces of stellite were wedged into the case where the lobe rotates

Camshaft bushing looks scored. Only on lower half.

If you look along the middle line in the case it looks like there is surface pitting on the case. Is this just the casting or forerunner of further case damage?

Blue750 · Dec 29, 2018

Rods have nicks. There are filing marks from the PO on the rods.

Top rings came out broken. Unrelated to the stellite but explains the excessive blowby I had towards the end.

Blue750 · Dec 29, 2018

One of the lobes shows visible wear with a step but it's not the lobe corresponding to the broken follower.

Lobe of the broken follower is the the left most.

Ding in flywheel

Blue750 · Dec 29, 2018

Ding in case. Flywheel hitting parts of stellite?

Have not measured journals yet.

Have sourced a new barrel with very low milage within original production tolerance and and hone marks still visible. Also have the corresponding followers. Will be rebuilding the engine over the next months. Considering long rods and maybe hotter cam. Should I start a separate build thread for this?

lcrken · Dec 29, 2018

Should I start a separate build thread for this?[/QUOTE]

Sounds like a good idea.

Ken

acotrel · Dec 29, 2018

Old motorcycles are like old people. As you get older, you have to do what you have to do to stay alive. While you are rebuilding it, make it better.

Issue in valve train

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