[ExKellick]

For all those gurus out there can anyone confirm if I need a top end rebuild.

A bit of history.

At the 40,000km service I checked the valves and on #3 the clearances were almost gone indicating Valve seat recession. (I believe this is a common fault on my year)

I also was running Pipercross air filters (foam) and I suspect the engine was ingesting more junk than normal which may have contributed.

Anyway I re did the shims and brought the clearances back into spec. All good.

Recently the bike has been doing a strange wheezing type thing (kind of like a misfire) every now and then which seems to be getting worse.

Today I hooked up a Carbtune manometer thinking it would all be just a matter of rebalancing the throttle bodies. At first indication #3 vacuum was much lower than #1 & 2. 1 & 2 were reasonably close and balanced easily. When I went to bring #3 up to meet them the wheezing I was hearing increased as a kind of backfiring out of the throttles of 1 & 2. The only way it will run at the moment is if #3 is left at a much lower vacuum otherwise it eventually cuts out due to a kind of misfire.

My guess is that the #3 valves or seats are no good due to the VSR and need remachining and lapping. A compression test would probably confirm this but I almost think it's not necessary.

Any ideas? I would appreciate any feedback - preferebly that which finds a simple inexpensive solution.

 

[dolson]

If you are thinking a compression loss a leak down test would be your best test to see exactly where the air was going. Basically though, an engine wears sort of evenly. If you correct only one area (valves) it will pump harder out or past the other (rings) so you have to do both top and bottom ends to do any real good.

 

[ExKellick]

Dolson, thanks for the reply. I kind of figured a leak down or compression test would be the only way to be really sure.

The thing that intrigues me is that only one cylinder is significantly down on vacuum which makes me think the recession of the valves in that head may be causing it. I can't imagine why one cylinder would wear more than the others though.

The other strange thing is the weird coughing as though the timing is out or something - is this likely on an EFI engine? Could the TPS or crank angle sensor be on the way out?

I want to rule out any other potential problems before pulling the engine to bits.

If its just the valves that are excessively worn due to manufacturing I would think it ok to just do the top end. I know it can cause piston ring blowby on a high mileage engine but I'm thinking 40,000kms is not that much and the rings should still be fine - notwithstanding excessive wear.

Anyone have any ideas on the coughing thing?

 

[frider]

Not that it helps your specifics THAT much...but this was a well known/documented fault with the GPZ900R ( ZX900 Ninja , over here?)

My soft valves/ guides on the inlet side sunk ever deeper into the head/reduced clearance around 75K Miles...Kawasaki UK actually paid for the parts, ( after a bit of arguing, as I had no 'dealer stamps ' on such an old bike.......and after I rebuilt the top end, my Geep9 went on to 125K, then the crank let go.......but, it had a hard life as a despatch/ euro tourer hack......!!!

I wish Triumph would 'step up' and recognize some of these recurring problems, that a few of us seem to have......heck, they even replaced the WHOLE carb bank, as a 'carb icing recall' around 85,000 miles on my particular Bike!!!

 

[ExKellick]

Phew - Head not dead, but still not quite right.

Over the weekend I went through the whole top end shamozzle. Rigged up a super duper compression test adaptor out of a bit of copper pipe my 6 year old found in the back yard, and old spark plug and a brass fitting I had been keeping for a rainy day. Upshot is the head is good, the valves are good and my timing gears on the cams were out by one tooth.

This is too easy to do on a 2000 Sprint. Note for the future - the timing arrows MUST be exactly in line with the head (in fact the head cuts the arrows in half). Now this is fixed the bike pulls away much better at power. The problem the throttle balance is still not coming together quite right and I still seem to be getting some kind of misfiring when I bring #3 throttle in line with #1&2. (can see it misfire in the throttle body intermittantly).

I have checked, injectors, valve clearances (again), timing pick up gap and all the electrical connections. Plugs are good but the resitance on the coil seems low (not sure if my multimeter is on the way out though).

Current symptoms are uneven idle (checked idle control valve) and surging accompanied by a bit of an odd burble from the exhaust at low speed (60km/h) which seems a bit like it is not firing properly. Top end and under power seems great.

I haven't been able to check the TPS properly. Could it be this, and could the Triumph gameboy pick it up? Could there be something going on in the computer? Could the coils be dodgy?

The MIL lights all reset ok after while.

Any ideas.