14 replies to this topic

[Jester422]

Hi

 

I have a 2000 registered TDM 850 with 27K on the clock which has a problem I am really hoping someone can help me with.

 

It started as a rapid knocking sound at around 2500 - 3000 rpm which sounded like it came from the top end of the engines (although this is hard to identify). Along with the noise was engine hesitation and short fluctuations in rpm even though the throttle was steady making it very difficult to hold a steady 30 mph around town unless you dropped a gear to rev it higher.

 

The bike went back into the garage I bought it off and they stripped the engine, replaced the Cam Chain, Shells, Big ends, Coils and Emulsion tubes but after rebuilding the engine the noise is just the same. There was no evidence of any bearing failure or metal in the oil and the garage say they could not find any particular wear on other components.

 

Below 2500 or above 3000 rpm the bike appears to be fine and the noise is either not noticeable or not there.

 

Any help would be appreciated  as all my local contacts are baffled.

 

 

 

 

[Studley Ramrod]

  to the club Jester.

 

 The fact it's only occuring between 2500-3000rpm would suggest a carb problem but I'm only guessing. Did it just start happening, or has it got worse over time ?  Anything done, or happened to the bike prior to the problem ?  Has the bike been stood for a good while ?

[Jester422]

Thanks for the reply and welcome.

 

I have always wanted a TDM, passed my direct access about 12 months ago, ran straight out to a local Bike shop and bought the a lovely looking silver TDM with Motad Exhaust system Belly Pan, extended front screen and heated grips. The bike had 21K on the clock and apart from a warped front disk was immaculate in looks. The noise was not so apparent when I first got the bike but I did have the irregular 2500-2300 rpm 30 Mph difficulty, however as I had not ridden a 850 before put it down to a twin / my inability to handle it.

 

As a matter of course I had the garage change the plugs, oil and all filters including air, they replaced the warped disk which did make the bike feel better.

 

I had one breakdown in torrential rain and had to have one of the coils replaced, again to be complete I had them both replaced which cured that particular issue.

 

As I grew more used to the bike I started to be more aware of the engine noises and the 'knocking'  became apparent at about 24k, it has not got worse or less for the remainder. That said I have only really just associated it with the low end irregular jerking. With the bike at a standstill and in neutral and slowly increasing the revs noise starts at 2500 rpm at which point the revs can fluctuate by about 100 rpm at the same time as the noise occurs, which kind of rules out anything to do with the clutch and gearbox. During the garage rebuild they fitted a new Yamaha (not OEM) cam chain and new tensioner along with New Pistons, rings, shells and big ends, there was no obvious wear in the little ends (as I had considered piston slap against the head).

 

As the bike has had such a complete rebuild with new parts I am loath to give up on her, especially as apart from the low rev noise /  hesitation it pulls like an express train further up the revs but I am concerned that something is wrong and dont want the engine to give up on me.

[Jester422]

Sorry to answer your questions, I have had the bike for twelve months nothing happened from my perspective that can be associated with the problem, I have always kept oils and water levels correct, 

 

The bike i is regularly used two - three times a week and I have covered over 6000 miles in the last year don't believe in just fair weather riding.

 

Tick over is perfect, no noise or hesitation as if I can get the bike to hold 30 mph at 2000 revs the ride is fine, like I said over 3000 and it pulls and rides without any hesitation.

 

I do not  go into the ref line (probably due to my age and lack of disposable income).

[TDMick]

  to the madhouse!

 

 

Could it be a fueling problem, something associated with the TDM engines well know dislike of 2000 - 3000rpm rev range?

Try setting the carbs a bit richer low down?

When I rebuilt my carbs on the Mk2 I set it up to be a bit rich low down and it pulled from tick over all the way through to the red from then on.

 

If it had been damage due to a previous owner letting the oil go low, I would have thought it would have gone pop by now, even with new big ends?

 

Edited by TDMick, 17 October 2015 - 11:14 pm.

[schmo9]

Needle jets maybe....my mk1 was rough under 3k, giving the impression of the odd clunk and jerkeness. Changed needle jets and now all is well.

[Catteeclan]

Don't these MK2s have a throttle potentiometer? Bad signal to the ecu could upset the timing.

[dablik]

Carb rubbers airtight.......!!

[Jester422]

Cheers everyone.

 

Great to have feedback on this one, when I got the bike I noticed the oil was very low and topped it up as soon as I got home. As you say if this had been a prolonged low oil situation I would have thought it would have died. Interesting the mention of problems even if the shells have been replaced, what would be the failure point if the engine had been mistreated before my ownership?

 

I am interested in the potentiometer comment, how does it interact with the ECU, i.e. does the ECU compensate timing based on the potentiometer signal and if so could mechanical noise be mistimed ignition based on a faulty signal at low revs? If this is faulty how easy is it to replace and what is required to set it up properly?

 

With reference to the Carb Rubbers, would a small leakage or split cause irregularity at low end only, as the bike appears to run fine up to the higher revs with no apparent loss of power.

 

I have seen people comment on raising the needles, could this be necessary if after market exhausts are fitted (as is mine) or does the bike require different jets altogether? I agree that if I keep a bit of choke on the bike does appear to be a little smoother at low revs.

 

Once again thanks for the replies.

[dablik]

Re carb rubbers, it's a possibility, had this on my old mk1 and put some additional tape around the bottom to make it air tight (tighter fit) hey presto solved the problem your describing, exact same thing, not necessarily your problem but worth checking.

[schmo9]

Re needle jets... my needle jets were worn causing too much fuel at low revs, giving your symptoms but you have stated that more fuel smooth's out your problem so maybe not them in this instance.

[Jester422]

I suppose a good all round check of the carb's to start with although the garage say they replaced the emulsion tubes when the engine was rebuilt.

 

I am interested in the potentiometer and Engine management system as there were initial electrical problems with corroded wires under the tank. It would be good if I understood what this system does in order to judge its impact on the engine / carbs. 

 

Is pre ignition possible on these engines as it kind of sounds a little like that type of sound and would cause the fluctuations in rpm?

 

Anyhow it seems everyone so far is suggesting Carb's and / or Mixture so its a good place to start. 

 

Going to start working through the solutions and keep the post updated with results.

[Studley Ramrod]

There's a throttle position sensor (TPS) see Haynes Manual chapter 5.5 + 5.6 section 7 for a full description of how it works and how to check it.  It performs a self diagnostic for failure or wiring fault, if there is a fault the tacho will display a routine showing 0 rpm for 3 secs, then 3000 rpm for 2.5 secs, then actual rpm.

[Jester422]

Evening everyone.

 

The TDM is back in the garage and I have just spent the last couple of hours with the owner looking over the old girl.

I relayed everything that has been discussed in the forum and we were using an acoustic sensor to pinpoint the engine noise.

According to the results the noise is nearside upper piston area and is very noticeable at  2500 -3000 as suspected.

Gas analysers were put into the exhaust system to check if there were any differences in emissions when the knocking takes place which may indicate ignition / carb's.

So, no fluctuations in emission whatsoever, not even a flicker, of course I cannot rule out two faults but the bike revs change at the point the knocking is heard.

They are going to attach a CAP monitor system to see if there are any fluctuations in ignition timing / strength although the lack of emission change does not indicate problems.

Following that they are going to strip the top end again but this seems overkill if they are certain little ends, pistons and valve gear looked and felt ok.

[TKH]

Could it be a sticking valve?/ worn cam?