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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 3 Sep 2007
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engine woes

hey - anybody with any ideas on this one -
I am going into the fourth day of this problem with the mechanic and the electrician - dont seem to be getting closer to solving it.
Bike starts perfect from cold, runs super for 20 minutes or so and then in an instant runs rough and immediately cuts out. I then need to leave it 5 minutes before it will start again. After this first cut out it cuts out every 2 or 3 minutes ( with those 5 minute breaks in between) all the time the intervals becoming shorter and shorter

Even though the engine is crazy hot we found that it was easier to restart the engine quicker with the choke pulled out - imposible without !

Engine seems to be running incredibly hot ( after 30 mins) - even putting a cold spark plug removal tool in for 2 seconds results in your fingers almost getting burnt from holding the moments earlier cold spark plug tool.

noticed this cutting out problem first whenever i attacked a steep incline - this is a sure way to bring it on.

Sometimes when it cuts out you can immediately hear the fuel pump tick ticking for a few seconds as if there is no feul in the pump but this anomaly is only intermittent

Electrical or mechanical?


Bike is yamaha tenere 89
Recent work - recoiled stator, crankshaft straightened and new crankshaft bearings and thorough carb clean (500kms ago)
new piston, timing chain and valve seals (1000kms ago)

new piston was standard yamaha but too small for cylinder so cylinder had an inner sleeve soldered in to facilitate fit - (never sounded great from day it was replaced to be honest - loud)

Im presuming the electrician has it wired correctly as it sounds and rides perfect for those first 20 minutes . .


Any ideas would be really appreciated -

from the darkest of perus

thanks

f
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  #2  
Old 3 Sep 2007
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E or M?

Can only point you in some directions to check:

1. Hot engine:
- This can be generally a sign of a very lean mixture. Are you sure that the carb settings are ok (all washers under the needle clips where they should be?) , the inlet rubbers in good condition, sufficient fuel flows to the carb? (tip: bypass the fuel pump; that's one source of problems eliminated.
This is supported by the fact that restarting is only possible with choke; although most likely the idle mix screw is set incorrectly.
Further, check the float level: if it is far too low this also leads to a lean mix.
2. Hot engine 2:
You've been tinkering with the stator. Is there any way you could have, by accident, changed the ignition timing? If it is advanced too much, this could also lead to a hotter engine. You can check the ignition timing with a strobe light.
3. fuel pump ticking after engine stop: unlikely, it is operated from vacuum from the inlet; engine stop = pump stop
4. Sometimes stators fail when hot as the higher temperature makes things expand and cause short circuits. If your bikes cuts out as you describe; do you have a spark at that moment?

Good luck!
Auke
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  #3  
Old 3 Sep 2007
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Another option could be the ignition unit (CDI) damaged, you could try, with cold engine, to heat the CDI with a hair dryer (the right temperature is until you could keep in your hand), and then start the engine, and verify if the problem happens immediately.
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  #4  
Old 3 Sep 2007
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Just check the fuel tank is venting, and not causing a vacum. easy to check just take the fuel cap off and listen for a air being sucked in, leave the cap off or loose and see it the problem continues.

Is the air box intake clear?

Steve
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  #5  
Old 4 Sep 2007
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engine woes update

auke, cyberzar, steve - thanks very much for the reply

The problem has taken a new twist. From this morning we couldnt even get a spark to start the bike - much cable swapping and re coiling of the Ac - Dc rectifyer ? ( the small box like unit connected to the stator ) eventually brought us to the stage of start up and the infamous 20 minute test run. Exactly to the minute the engine ran dog rough and cut out. Once again I could only return in fits and starts to the the waiting electrician.

What differed this time was the horrendous ´´animal squealing´´ type mechanical sounds that were coming from the mechanical innards of the engine whenever i tried to restart after this initial 20 minute engine stop/cut out.. On cutting out once more at eventual arrival at the electricians shop I attempted to restart the engine for him so he could hear. He immediately said that this was the sound of an engine with no lubrication. We pulled off one of the valve covers at the front of the engine and it and the immediate innards were bone dry. So is this it?

The engine currently has 2.4 litres of oil exactly. Dipstick reads 3/4 up the stick. So either the oil pump is broken/malfunctioning or I have a blocked oil hose ( this engine has been taken apart and regasketed - re siliconed more times than u could ever imagine - perhaps a possibility of gunk build up in the oil tubes?)

All this would explain the extreme heat of the engine block but which do you think it is - pump or pipes?

From what I can see from the clymer manual that i have for xt - tt 600s it looks like I have to remove the clutch first before dissasembly of the pump - should I start with the oil tank reservoir and the wire gause filter at the bottem of it before embarking on this oil pump removal road or not?

Over the last 48 hours and the hourly removal of the left hand crankcase cover i have been surprised by how little oil has escaped (ie none ) in all the times we restarted the bike with just a couple of bolts placed and tightened for testing ( old gasket - no silicone) . We always had the bike leaned 20 - 30 degrees to the opposite side of the stand but nevertheless I always remembered some oil escaping from previous operations like this?

So any ides about the best and most efficent way of tackling this oil circulation dilema would be hugely appreciated.

As an aside - i had to remove and bin the oil cooler on this bike in Santiago 5 months ago. The problem then was that the oil cooler was so blocked and damaged that it was preventing the oil from returning to the reservoir so as a result we could never get any dipstick reading at all ( We closed the loop with a new hose ) A blocked hose exploded and sprayed a litre of grey gunky oil all over a new VW and a very surprised taxi driver in the petrol station that day too!
This time round the dipstick is always reading good ( 3/4 to full )

Is there any way of testing that the oil pump is operational without draining the oil and removing the clutch? Or is there something else that I´m overlooking such as the electrician rewiring wrongly so that the oil pump has been effectively disconnected?



Once more . . . thanks all - in a continent of lousy mechanics you all are a light!

f
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Old 4 Sep 2007
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Wow

How mysterious things are becoming.
Let's concentrate on the oil first...
The oil pump is engine driven, so mechanical, no electrician sticking to his trade can prevent it running.

Let's do the following checks:
1. Oil in oil tank: check dipstick
2. Oil arrives at the oil line connection to the engine: there's a little flange on the L/H side of engine, below the shift shaft; if you loosen up the two bolts, is oil flowing out?
3. Start engine, loosen up the vent screw on the oil filter housing: oil flowing out?

Some thoughts: from the oil pump, the oil flows two ways: to the crankshaft / piston and to the head, to lubricate camshaft and valves. Oil flow to the piston must be OK, otherwise your engine would have seized up already. This leads to conclusion that the oil passage to the head might be blocked. But, first, do the checks as described above.

Auke
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  #7  
Old 5 Sep 2007
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results

hey Auke
checked the dipstick - 3/4 reading on the dipstick
Removed the two bolt flange from under the gear shift lever - barely a drip
Quick start and removal of the oil filter cover vent screw - no oil spraying out

Emptied the oil from the reservoir tank and removed the cylindrical wire gause filter - - ouch!

It was difficult to pull out - it was so thoroughly encased in a bullet proof sock of metal/aluminum bits, silicone and copper coil shards - not a pretty sight ..

Removed all oil pipes and cleaned thoroughly - drained the rest of the oil from the system and refilled with new stuff. Bolted up and went on a test run up the mountains.

Bike rode fine, no cutting out after 20 minutes which was such a novelty!

Stopped half way through to inspect and then became aware of the true cost of this escapade . . .

Base and head gasket shot - oil leaking everywhere . . . rode back easy to see what to do next.

We started to take the engine apart and slowly reveal the damage - cam shaft severely scored, the section of the head that the shaft sits on had pieces missing and sharp edges protruding

Cylinder ( my new cylinder !) has huge scoring on either side of it - top appears ok - fit is still good - tiny mm of play when attempting to shove side to side

Piston rod knocks alot - i believe its been this way a while as the engine has had a loud knocking sound as long back as I can remember - wasnt possible to replace 500 kms ago when I had the engine split and the crankshaft out as 3 weeks was the quickest time in getting one to that location . .

So we regasketed, filed away the ugliest of the shards and bolted up - I hope to hit the road for colombia direction tomorrow

What puzzles me is how the hell so much damage was caused to the cam shaft which in turn blocked the oil reservoir gasket - or is it the ¨which came first¨ the chicken or the egg dilema ?
- did the camshaft deteriorate due to lack of oil caused by the oil blockage or did it itself cause the oil blockage due to some other factor. 500 kms ago the camshaft was perfect when we had the engine split and reassembled from the crankshaft up - 2 days after this the engine started its overheating thing where it would cut out after 20 minutes. As it was the middle of nowhere I had to ride a further two days like this to get it to this town to fix. Am curious only for the sake of seeing where on the list this mechanic rates in my top 100 worst mechanics of south america ( Ive seen at least 200). Or maybe where this rates in my top 100 personal blunders of stupidity in not realising that I could have had an oil circulation problem . . .

Also do you think with the engine like this I can get another 7000kms to the carribean coast - I know it will probaby be a bit smokey but do you think it can function without much more trouble ?

thanks again for the advice earlier - as usual the mechanics here wanted to get straight into removing the clutch and oil pump without checking the obvious first - i took them through the 3 checks you posted and we saved ourselves alot of dead end time

cheers

f
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  #8  
Old 5 Sep 2007
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Well

In general XT engines are very difficut to kill, so I guess your chances of getting another 7000 kms out of it are 50 / 50. You'll have to stop every 100 of even 50 kms to check and add oil.
Since you are in South America, is it not a better idea to try and find a second hand engine that has not been through such a torture?
I think in Brazil XT's or Teneres are still being sold. Check for the Brazil XT or Tenere club, they might be able to help you.
Before you install it btw, check and clean oil tank and hoses.

The camshaft journals were damaged by lack of oil; so it is not the other way around.

Lots of luck and succes!
Auke
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