DR350 - Breakdown

[DrSmith]

Hi,

A couple of hours ago my DR 350 broke down. I was probably giving it more than I should have, then suddenly there was a huge loss of power, followed by a horrible engine noise and the eventual stopping of the engine altogether.

There was also smoke coming from the exhaust, quite a bit of it too.

When I pulled over I notice I could roll the bike forward while in gear with not much resistance from the clutch (albeit with a nasty clicking sound). This initially led me to believe my clutch packed up. But would this cause smoke emerging from the exhaust?

The starter motor also sounds like it isn't engaging. It's making the right noise for a starter motor but it certainly doesn't sound like it's turning the crank (the bike doesn't start, obviously).

When I got the bike back home, there was normal resistance when trying to roll the bike in gear. It felt like there was plenty of compression.

It's too late to start investigating now, but I thought I'd put my initial thoughts down here to see if it rang any bells with you lot.

Cheers.

[steo]

only a rough guess coz it could be numerous things that went wrong but sounds like you cudda bent a valve. would explain the sudden loss of power & smokey exhaust. it might feel like there's compression if the piston on its upward stroke is hitting a bent valve. interesting one that, let us know what the damage was.

[garyd]

i have a mate with lots o DR350 bits ,hes in Nottm
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[wizzzard]

My first thought would be a bent or broken valve. I had exactly the same symptoms on my little sr and it had bent the inlet valve and snapped it right it the top of the valve stem. My son was riding it at the time and he was giving it more than he should have been as well.

Not a difficult job to put right if it hasnt knackered your guide up although i couldnt say why it had done it in the first place other than general wear.

Good luck
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Zeitgeist / Addendum / Moving forward

[DrSmith]

Had a bit of an unproductive session in the garage today. Lots of bouncing around of ideas but nothing definitive.

My first time stripping a four stroke so I'm taking my time with it, doing it by the book.

There's a noticeable clicking when the crank is turned, very consistent and a very sure click - almost as if it was supposed to happen. Any ideas on what could be causing the clicking? We thought maybe the piston is catching a valve on its up-stroke. Could it be anything to do with the starter motor? Taking into account what I said previously about the starter motor not turning the crank...

I got as far as taking the roller arm/camshaft cover off. There's lots of wear on the roller arm pad (the bit that gets pushed by the cam) for the exhaust valves. This could be causing the exhaust valves to not be opening fully. I'm not sure sure what kind of damage that could be doing.

I then shone a torch down the spark plug hole and noticed a nice big chip/hole on the top of the piston. It'll need replacing. I hope there's not much damage to the barrel.

My thoughts on what could have caused that kind of damage were that it's probably a knackered valve. I'll find out tomorrow when I take the head off.

[Pete.]

The wear you're describing happens over time not instantly. Hard to diagnose from your description. Could be the conrod let go? You can check for a busted rod by pulling the sparkplug and putting a pencil down the hole until it touches the piston. Now turn the engine a bit by hand - if the pencil doesn't move you've rodded the motor.

What does the oil look like?
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[DrSmith]

If it's a test to see if the piston travels up and down then I can tell you it does. Shining a torch through the spark plug hole lets me see that much.

[Pete.]

Hmm, well if the piston's moving and the valves are in place and the cam's turning then you've either popped the piston, twatted a valve, or blown a gasket. Your description of some of the symptoms still doesn't help diagnosis. Does the bike have a de-compressor?
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[garyd]

Gonna be alot easier to put another engine in ,you were given the number of my mate ,phone him and ask about an engine
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CRF230 all you need

[DrSmith]

I found the problem; there's a nice big hole in the crown of the piston. Pics to follow...

Question is; what could have caused it? If the worn rocker pad was causing the exhaust valves to not open fully, would this cause such damage to the piston?

Also, anyone know where to pickup a piston and/or rocker arm for a DR350? Wemoto don't seem to stock them.

[bikersupermot...]

was the bike/engine overheating at the time? ... when u say u were giving it more than u shudda ... what were u doin to it?...an how?
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tinybikes

[bikersupermot...]

was the bike/engine overheating at the time? ... when u say u were giving it more than u shudda ... what were u doin to it?...an how?
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tinybikes

[DrSmith]

Overtaking a moped. Nothing silly, just giving it lots of beans.

What are the symptoms of it overheating?

[dan3411]

[bikersupermot...]

[DrSmith]

Pics as promised;

https://ryaneffigy.com/images/piston1.jpg
https://ryaneffigy.com/images/piston2.jpg
https://ryaneffigy.com/images/piston3.jpg

[Pete.]

Piston is well-popped
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[DrSmith]

Indeed it is Geri.

220 pounds worth of stuff coming from our Dutch friends at CMS. They're a little pricey, but they stock nearly everything. Even specific bolts and washers.

Piston, gaskets, rocker arm, plus a few other bits and bobs I've been meaning to replace. Does anyone know how long they usually take to ship to England?

Someone on another forum suggested heat erosion as the cause for the damage. I'm not sure if there is anything in particular I could have done to prevent it, as I'm still unaware of what caused it. Not an ideal place to be in on reassembly.

[garyd]

Sorry Dr my bad,thought it was you i sent the number to
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[steo]

usually when you hole the piston but not by mechanical means i.e dropping a valve, its only caused by a few things but more commonly poor detonation caused by continually using the wrong heat range plug or a lean fuel/air mix. i would go with the latter & richen up your fuel mix.

[DrSmith]

steo, that's a good point, and one which I've already considered. However, when I pulled the plug shortly after the break down, it was fairly black - which would indicate a rich mix.

Are there any other ways of testing for a good mix?

[steo]

the colour of your plug after the breakdown wouldn't be a good indication of how rich the fuel mix was. you said that there was smoke coming from the exhaust so it could be sooty looking from oil & fuel being burnt together plus u would have been fowling the plug kicking the bike trying to get it started after it stopped. put the engine back together & bring the bike for a good run then check the plugs colour, you want it a nice gold brown colour for the right fuel mix..

[DrSmith]

Good point, I forgot about the burnt oil.

Hopefully I will have it back together by the end of the week. I'm taking my head to a shop tomorrow to have the valves done, I'm also waiting on a delivery from cmsnl.

[steo]

what are you getting done to the head? if it's just grinding in new valves, you'd do that yourself in an hour.

[DrSmith]

They're charging £2.50 a valve. I don't mind paying a tenner for something like that.