Hitchcocks Forum

Out this afternoon testing some changes to the bike when I think something broke. I was travelling up a gravel track when I heard what sounded like a rock trapped behind the ally mudguards and rattling around. After a while it hadn't gone away so I stopped and took a look at the bike but everything appeared in order. When I set off again it was still there so I pulled up knelt by the side of the bike and revved the engine. It sounded like someone dropped a nut into the engine and it was rattling around inside. Bugger!

I couldn't leave the bike half-way up a hillside so I had to ride it back home (around 15 mins). The bike ran OK but still rattled all the way back.

I've ordered the gaskets to start pulling the engine down but I wondered if anyone had experienced anything similar so that I can start with some of the more obvious failures?

Stuart

You don't say what model you have.

You didn't say what bike.

If it was my pre-unit bullet I'd check simple things first.

I'd check the tappets first off.

Primary chain tension (finger in through the filler hole).

Engine mounts (lever between the engine and frame with a prybar, see if it moves).

Loose exhaust (blowing at the header can sound weird).

Loose sparkplug (as above, they run surprisingly well with a loose plug).

Speedo drive cable.

Loose bodywork.

Alloy mudguards are terrible for making odd noises that don't necessarily sound like they are coming from there so your first thought may be right. Try removing it ans see if the noise goes away.

Final drive chain hitting the swingarm/chainguard.

Sorry guys, 350 pre-unit from 2001 with carb.

Does the frequency of the rattle rise and fall with the revs of the engine?
Does the engine still perform reasonanly well or does it hesitate to rev?

If both of the above are true I would suspect tappet adjustment, or assuming the rocker spidles are mounted in blocks as per the 500 that one or more of the nuts may come loose allowing the rockers to rattle about.

I had the ex tappet slacken itself off on the 612 last year, managed to limp home very carefully but the engine would not rev and was as flat as the proverbial witches t*t. Mind you with something clearly not right I was not going to thrash it.

Could be totally wrong and I hope that you soon find the cause of the rattlle.

Cheers.

The engine is quiet(ish) at tickover but rattles when revved. I didn't test the performance on the way home but it's a 350 so it barely has any to start with! There was one anomaly - I backed off for a corner and it coughed and almost died. I whipped the clutch in and revved it and it kept going. The stumble wasn't repeated but luckily I didn't have to slow for any junctions.

stinkwheel wrote: ↑

Sun Feb 23, 2020 6:34 pm

I'd check the tappets first off.

SW, what made you go to tappets as the no.1 of your list? Just curious as Andy also went there.

Also when you say tappet do you mean the rocker block or are you thinking push rod adjustment?

Stuart

Hope no one minds I also was going to say tappets first check
Take off adjustment cover to check

The reason being they can and do back themselves out of adjustment also they are awkward to tighten the lock nut up if you leave the cover holding stud in place when setting them

Hope I haven't upset anyone
And this helps Dai

In my case I simply did not tigthen the exhaust tappet adjuster up tight enough, it loosened itself so I had a huge Ex tappet clearance with symptoms very similar to what you describe.

The block I was referring to is the one on top of the head that the rocker shafts fit into. On the 500 these are held in place by 4 studs / nuts if the nuts were to come loose then the rocker shaft could move around.

As I say could be totally wrong.

Cheers.

Thanks guys - it’s supposed to snow tomorrow so that’s my day sorted out.

3 votes for pushrods so I’ll start there.

Stuart