Bike over heating after 40 mile ride

[Ken4004]

https://youtube.com/shorts/fo1BwZChoxk?si=zYPBbhgGbNOJM228


Bike carbs sync these don’t look bad to me they were well out but not surprising as I had the carbs apart

[Ken4004]

Everything set up again today so just to recap :-

The fuel cap breather is working correctly

The oil filter and oil strainer are clean

The spark plugs look gaps are correct

The timing has been reset and checked with a timing light

The advance mechanism is moving freely and advancing the timing when revel up.

Carbs have been balanced with pro tune

The fuel is flowing freely from tank, removed fuel Tap a cleaned filter just a few bits on the filter.

Bike starts straight away and idles nicely at 1200 rpm

Bike revs up to 6000 freely ( haven’t gone past that as still running in) when not in gear



Wife has been very patient with me so need to get reading for our holiday so that’s it till I get back in a couple of weeks.

Jobs to do

Remove spark plugs and clean with a blow torch to clean up then go out for a run and see how she feels, thanks everyone for your input.

One last thing I think I need some new leads for my coils they are too short on number two cylinder and the spark plugs caps need changing, there is a possibility that I might  be getting an occasional misfire on number two cylinder because of the ht leads I think.

Can anyone recommend a new set of coils for my 400 4 that are decent , original coils are ok but leads are moulded  in so cannot be changed so ideally I would like some coils that I can change the leads on when they get ropy.

[Ken4004]

Alternatively if someone has a set of coils they are not using I could fit them to my bike and modify the originals in slow time

[TrickyMicky]

No disrespect, but even when running in, if you do not go above 6000RPM, then you are not doing it any favours, they don't even start breathing properly till about 7000 or 7500, so if you were going uphill in top gear at 6000 or less then, yes, you could overheat as you are virtually labouring it. You mentioned your other bike which is no comparison whatsoever with the 400, which has very small pistons, very oversquare dimensions allied to no flywheel. They do need to be kept spinning at a reasonable rate.

[Ken4004]

Hi Tricky that’s a very good point , I didn’t really think about this particular road being an issue but from what I have read on this forum this bike needs to be reved hard so really I wasn’t giving it a chance.

I haven’t wasted my time re running through the set up because things had changed and needed to be tweaked while the bike settled down after the rebuild.

Had a lot of issues fitting the exhaust the first time because it was from another bike but once fitted and heated up it was relatively east to remove and refit.

Next time I go out for a ride I’ll give it some more revs just being over cautious I suppose.

[McCabe-Thiele (Ted)]

Everything set up again today so just to recap.

Can anyone recommend a new set of coils for my 400 4 that are decent , original coils are ok but leads are moulded  in so cannot be changed so ideally I would like some coils that I can change the leads on when they get ropy.

I fitted Dyna S coils as part of their electronic ignition kits,  I adapted the existing coil brackets to make the Dyna coils fit.

[TrickyMicky]

We've all been there Ken, but if it's any consolation, I've just dug out my original owners handbook, and it advises for the first 600 miles, do not exceed 8000RPM, and that's with everything being brand new.  Enjoy it!!!

[Ken4004]

Thanks For the info I’ll open her up a bit more, I must say I am very impressed with the handling around the bends it really inspires confidence.

[McCabe-Thiele (Ted)]

This is an interesting looking bit of kit - not cheap, with Boyer-Bransden name.
www.ebay.co.uk/itm/364680555365

[Ken4004]

I noticed yesterday that no 2 exhaust pipe warmed up a little slower than the test although it seemed to start OK so I believe the cable / plug on no 2 is occasionally breaking down.
The leads on all plugs are a bit short like they have been shorted a number of times so time for new hardware .

[K2-K6]

I noticed yesterday that no 2 exhaust pipe warmed up a little slower than the test although it seemed to start OK so I believe the cable / plug on no 2 is occasionally breaking down.
The leads on all plugs are a bit short like they have been shorted a number of times so time for new hardware .

That rings alarm bells for a poor running cylinder. Given that your other investigations have not given anything confirmed as probable cause, that partially missing cylinder needs investigating for both ignition and idle circuit fuel supply.

If you have a borescope it would be worthwhile looking in there to see if there's anything untoward.  The cheap type for phone, with front & side facing camera are really good value to get decent inspection.

Hope you have a good holiday, anywhere interesting  ?

[Ken4004]

I noticed yesterday that no 2 exhaust pipe warmed up a little slower than the test although it seemed to start OK so I believe the cable / plug on no 2 is occasionally breaking down.
The leads on all plugs are a bit short like they have been shorted a number of times so time for new hardware .

That rings alarm bells for a poor running cylinder. Given that your other investigations have not given anything confirmed as probable cause, that partially missing cylinder needs investigating for both ignition and idle circuit fuel supply.

Off to Kefalonia in Greece for three weeks , going around the whole Island staying one or two nights in several places so should see the whole island,

I was looking at endoscopes a couple of months ago and thought it might be useful bit of kit and it appears that I was right , I did a very detailed and meticulous clean of the carbs when I had them off the bike but as I said before I am not ruling anything out.
I was going to change the coils anyway in the future because of the dodgy looking leads so this is a good a time as any to get it done and cross another possibility off the list.

Thanks for the advice regards Ken

If you have a borescope it would be worthwhile looking in there to see if there's anything untoward.  The cheap type for phone, with front & side facing camera are really good value to get decent inspection.

Hope you have a good holiday, anywhere interesting  ?

[Ken4004]

I think you have an electromechanical gremlin that stoped the engine and starter didnt work

Still in gear and clutch lever not pulled all the way in. We have probably all done it much to the annoyance of cars behind us.

Dave

I have just got back from holiday and went out for a ride and 10 miles in the bike  overheated again and died at a junction and you were spot on Dave , the bike would not initially start but I then remembered what you said and realised that I was in gear and started it again straight away but it was hesitant and would stall at low revs so nursed it home.

I did have my suspicions about no two cylinder not firing properly and so decided to look at the plugs again and every plug looked fine except no two cylinder which was sooty.
On another post I did talk about changing the HT leads on the coils as per Ash’s modification and have bought all the parts needed for the mod.

So just to let you know what I found , whilst  preparing the coils reading for fitting the new cables I thought I would first check the resistance between the leads between 1 and 4 which came out at about 24 ohms with the caps fitted and 14 ohms with cable only so what I expected.
When checking the 2 and 3 coil no resistance so open circuit and after stripping back the insulation found that the HT lead was broken half way down and showed signs of corrosion, just pulling on the lead it was stretching so I knew the wire had completely broken.

So in a nut shell when originally checking for a spark all plugs  looked good so assumed the leads were OK but a little short , when starting the bike for the first time noticed that number 2 cylinder exhaust pipe was not getting hot straight away then finally after a few minutes got up to temp leading me to suspect the HT lead.

Bike has done about 200 miles after the rebuild and didn’t seemed to me to be pulling as it should so must have been only running on three cylinders most of the time which would explain a lot.

Anyway in the process of repairing / replacing all HR leads on all coils which will take a couple of days due to waiting for expoxy and putty to dry and then I’ll get it all back together clean the plugs check the HT resistances and take it for another spin and see how it goes.

I am not really sure if running the bike on only 3 cylinder would cause the engine to overheat but sounds very plausible because the other working cylinders are working extra hard .

[K2-K6]

Hopefully you'll get to the bottom of it with the coil rebuild, then verify its firing properly on all 4 cylinder.

Running on three will cause it to be a heat risk, as you've found. They've only about 24 ft/lb of torque @ 7500rpm when healthy, so starting with approx 18 lb and running below peak torque will likely bring about 15 lb at a, licked finger in the wind, estimate.

Trying to pull uphill like that will severely compromise its output, ultimately to cause lean running through that set of circumstances.  Essentially, the crank rpm can not "follow" throttle opening as there's insufficient torque to accelerate the bike and rider. That causes you to open the throttle further, which drops the vacuum affecting jets, to then run permanently lean (if the crank rpm  never catches the throttle slide position) up gradient being the biggest risk, as it can never catch up.

"Lean" running, in and of itself doesn't necessarily increase heat as a cause. What happens as the combustion  chamber reaches its ability to burn fuel as it approaches the 14.7:1 ideal (stoichiometric) the propagation of flame front outward from the spark plug begins to break down such that the burn phase doesn't spread out to far reaches of tbe periphery of piston/chamber. This results in unburnt "gas" mixture in a ring around that periphery, which then explodes rather than burns as piston comes to tdc. Its this uncontrolled event that gives a shock wave that breaks the boundary layer protecting the piston crown from exposure to high heat and subsequently raises the overall temperature if left unchecked.  When more extreme, we can hear this as "pinking" but it starts in virtually inaudible levels before we become aware of it in more severe form (we're isolated from source & with helmet sound insulation too) but it happens and significantly shifts the temperature accumulation, that also being relative to the ambient air trying to cool tbe motor and it's capacity if moving more slowly.  Detonation is the process, as there's loss of control thats fundamental to how the fuel air mix is supposed to combust, rather than explode. Essentially it has the effect of advancing the timing to detriment of the engine's desirable running condition.

There's another phase going on from this as too much of the above will likely bring pre-ignition, which is usually catastrophic, and in short time frame too  this will definitely put a hole in tbe piston for you!

Seems like you've got away with it in recent description, but quite close to serious damage though.

[Ken4004]

Hopefully you'll get to the bottom of it with the coil rebuild, then verify its firing properly on all 4 cylinder.

Running on three will cause it to be a heat risk, as you've found. They've only about 24 ft/lb of torque @ 7500rpm when healthy, so starting with approx 18 lb and running below peak torque will likely bring about 15 lb at a, licked finger in the wind, estimate.

Trying to pull uphill like that will severely compromise its output, ultimately to cause lean running through that set of circumstances.  Essentially, the crank rpm can not "follow" throttle opening as there's insufficient torque to accelerate the bike and rider. That causes you to open the throttle further, which drops the vacuum affecting jets, to then run permanently lean (if the crank rpm  never catches the throttle slide position) up gradient being the biggest risk, as it can never catch up.

"Lean" running, in and of itself doesn't necessarily increase heat as a cause. What happens as the combustion  chamber reaches its ability to burn fuel as it approaches the 14.7:1 ideal (stoichiometric) the propagation of flame front outward from the spark plug begins to break down such that the burn phase doesn't spread out to far reaches of tbe periphery of piston/chamber. This results in unburnt "gas" mixture in a ring around that periphery, which then explodes rather than burns as piston comes to tdc. Its this uncontrolled event that gives a shock wave that breaks the boundary layer protecting the piston crown from exposure to high heat and subsequently raises the overall temperature if left unchecked.  When more extreme, we can hear this as "pinking" but it starts in virtually inaudible levels before we become aware of it in more severe form (we're isolated from source & with helmet sound insulation too) but it happens and significantly shifts the temperature accumulation, that also being relative to the ambient air trying to cool tbe motor and it's capacity if moving more slowly.  Detonation is the process, as there's loss of control thats fundamental to how the fuel air mix is supposed to combust, rather than explode. Essentially it has the effect of advancing the timing to detriment of the engine's desirable running condition.

There's another phase going on from this as too much of the above will likely bring pre-ignition, which is usually catastrophic, and in short time frame too  this will definitely put a hole in tbe piston for you!

Seems like you've got away with it in recent description, but quite close to serious damage though.

Many thanks for the detailed explanation , I have modified the coils just waiting for the Milliput epoxy putty to dry then just a matter of rubbing down and painting then checking coils and fit back on the bike snd see what happens.
Will probably check the timing again and the carb sync because this will all be affected if I was only running on three cylinders some of the time.
I did notice that when setting up the timing with a strobe it was occasionally jumping around which was probably due to the misfire on number two spark plug.

This has been an interesting problem and it’s very easy with any issue to jump to the wrong conclusions.

When I originally bought the bike and rode it home from Barnstable to Copthorne Sussex it seemed ok but when I got around the stripping down the engine I found a piston and I think it was two had quite a bit of heat damage where the head of the piston was partially vaporised.
I originally believed was due to a piston ring being broken but it’s all making sense now.

Obviously during the rebuild I did change piston two and fitted new piston rings to all cylinders.

I will try and see if I can get hold of a endoscope camera to look at the head of the pistons thru the spark plug hole to see if there is any damage .

This is my first bike rebuild so it’s been a learning curve , I originally just checked for a spark on all cylinders and didn’t check the coils resistance so lesson learned .