Increased engine chatter - Decreased power

[Moarpower]

Hey guys.

Went for an afternoon ride. The 80gs850 was running beautifully. Ride was about 2.5 hours.

I stopped for fuel and noticed a lot more noise from the engine. I also noticed that power seemed to have dropped quite a bit.

I'll check valves this weekend but it seems like a very sudden change and the power decrease is quite noticable.

It might be best for me to pull the motor and do a full inspection

https://youtube.com/shorts/6pPV2HXRi-g?si=ulnXc5E6ZwrN8Wgd

 

[Rob S.]

Valves? 'Cam walk'?

 

[Moarpower]

Valves? 'Cam walk'?

Cam walk was present already. Definitely could be valves but the sudden power loss is the concerning part to me.

 

[Grimly]

Before you start pulling things out, check the compressions.

 

[Moarpower]

Before you start pulling things out, check the compressions.

Compression is good on this one for its age.
160, 155, 160, 165

 

[Moarpower]

Well upon measuring 2 of the valves...clearance has made its way up to 0.11mm on the intake side

 

[Moarpower]

Ok guys......I might be mistaken but is there something seriously wrong with this picture? Intake cam and ex are reversed.
Now I know on some later models swapping cams can give you a boost, but that's usually swapping an intake in to the exhaust and keeping the existing intake in place.

EDIT- Upon inspection I can see the worm drive on the from for the tachometer. So the gears themselves or on the wrong cams. Could this cause an issue or are they the same ?

 

[Moarpower]

https://youtube.com/shorts/Uiz5H9-YqoI?si=fCr8ZxmtvIXT-pAA

Here is another issue I found
The chain hops as it meshes with the top idler gear.
Definitely a source of noise.

 

[Moarpower]

Here is a more detailed video.
At the point where the chain jumps it actually loses tension.
So this combined with valve clearance and the sprockets being on the wrong cams would certainly lead to a lot of noise and poor running conditions?

https://youtu.be/TRP12C6VG6k?si=Ac_iX5f09lkvnNt4

 

[Grimly]

Here is a more detailed video.
At the point where the chain jumps it actually loses tension.
So this combined with valve clearance and the sprockets being on the wrong cams would certainly lead to a lot of noise and poor running conditions?

https://youtu.be/TRP12C6VG6k?si=Ac_iX5f09lkvnNt4

I'd not be surprised if some joker hadn't fitted the wrong pitch of a top sprocket.
Check the chain pitch too, and definitely put the proper sprockets on each cam, just to keep it right.

 

[Syd]

Wow - You're onto something there.

 

[Moarpower]

I'd not be surprised if some joker hadn't fitted the wrong pitch of a top sprocket.
Check the chain pitch too, and definitely put the proper sprockets on each cam, just to keep it right.

It looks like they'd slotted the holes in the sprocket too. That's going to make things even more of a pita for me to dial it all back in as I'll have to degree it.

What do you mean by checking the chain pitch ?

 

[rphillips]

Yyou say bike was running good, when you restarted after fuel stop and felt power was down, if the sprocket slipped in those elongated holes, when you restarted it, it will change the power. how much depends on how far they slipped... Hard to imagine EX. sprocket on IN. cam, but you've sure got a picture of it.

 

[Grimly]

What do you mean by checking the chain pitch ?

The distance between links - measure say, 20cm and count the number of links. One of the manuals has a pitch measurement that's allowable.
Needless to say, a new chain should be in spec and a worn chain won't. Neither will a totally wrong one.

 

[KiwiAlfa156]

Here is a more detailed video.
At the point where the chain jumps it actually loses tension.
So this combined with valve clearance and the sprockets being on the wrong cams would certainly lead to a lot of noise and poor running conditions?

https://youtu.be/TRP12C6VG6k?si=Ac_iX5f09lkvnNt4

The tension on the chain should be constant through the full loop of the chain. The chain shouldn't have slack points/tight points. The auto (anti-reverse) cam chain tensioner would have to back (reverse) out in order for the cam chain to go slack at any point, or the tensioner is at the end of its travel and not taking up the extra slack, or is jammed/binding and not auto-adjusting at all. Whatever is the cause, a slack cam chain or one that's unevenly worn can jump a tooth (which could cause the issues you describe), which with the non-stock cam sprocket arrangement will make it difficult to determine whether it has or not. How far are you tearing the top end down?

If it were me, a new cam chain and inspection of the tensioner would be the top of my list. You can replace a cam chain by grinding out a rivet and winding/pulling the one through with the old one. Then rivet it together with the correct rivet link, it is not a hard job, and unless its a race engine, correctly done riveting is plenty strong as side load on the pins is minimal.

The index marks on the cam sprockets are are for ease of setting up the timing, but you can do it with a degree wheel on the crank and dial gauge to measure cam bucket movement. IF you know the inlet cam timing openings in degrees BTDC, and exhaust ATDC and the amount of lift at which those events are measured. Which is why there are the index arrows on the cam sprockets.

When I was finding a replacement cam for my 750, I did a lot of part number sleuthing and realised that Suzuki used a lot of the same cams across the 8-valve and across the 16-valve range, in various capacities. The different cams had the same external dimensions -apart for the lobe profiles (lift and duration). These were paired with a range of cam sprockets that were used to control other variables like overlap and cam timing in relation to crank degrees (earlier or later opening and closing). I had a 16-valve 1100EZ exhaust cam in my spares, that had the same part number as the 16-valve 750SZ, but had a different sprocket numbers between the two applications. The 750 cam that required replacement had larger diameter sprockets than the 1100 sprockets, due to the lower overall height of the engine. However the cam timing stated in the manual is different as well. Both uses the same 120 link cam chain.

The slotted cam sprockets are modified for vernier adjustment to allow the timing/overlap parameters set by Suzuki through its part number combination of cam profiles and sprockets, to be adjustable. Allowing the power to shifted between mid-range and top-end.

It's hard to know whether the reversal of the cam sprockets was an error, or possibly done on purpose as some way of attempting to increase performance. slotted cam sprockets, confuse the matter.

 

[GregT]

Simplest answer IMO is that someone dialled in the cams- to unknown lobe centers - and the slotted sprocket(s) have moved.
I'd also check that the tensioner is free to move as occasionally the lockscrew and nut on the side is used as a poor mans manual tensioner.
In combination, slipped sprockets and an immovable tensioner would give the symptoms you describe.