Dirtbike Question

[bilbo]

I've been trying to create an account on a dirtbike site but couldn't get it to work. So I figured I'd check with the abundance of knowledge available here! The DRZ125 I got for my son smokes pretty bad, so I figured it needed a new set of rings. We tore the top end down and found the cylinder to be in remarkably good condition. There's no evidence of scoring anywhere or anything and I'm hesitant to replace the rings. However we did find the bike was missing the head gasket and it looked like black silicone was used instead; not sure if that's a normal thing as it seemed to have decent compression and ran fine aside from looking like we were fogging for mosquitos. Is it possible that was causing the smoking? I was thinking of just cleaning up the head and replacing the valve seals, then calling it good. Anyone have any experience with these? I haven't messed around with a motorcycle in a long long time.

 

[Josh B]

I would call a shop that sells those same bikes and ask if they have a gasket for one, then just follow the conversation a ways

 

[RonD]

DRZ125 is a single cylinder 4-stroke engine with an overhead cam so could need new valve stem seals
So doesn't use oil pre-mix fuel, have to mention that

I would put in new rings just because head is off and it easy and not expensive to do

Yes, there should be a head gasket

 

[bilbo]

DRZ125 is a single cylinder 4-stroke engine with an overhead cam so could need new valve stem seals
So doesn't use oil pre-mix fuel, have to mention that

I would put in new rings just because head is off and it easy and not expensive to do

Yes, there should be a head gasket

I thought so, the parts manual calls for one and I’ve never worked on an engine that called for silicone for a head gasket.

I knew it was 4-stroke, no premix, that definitely wasn’t the issue.

I have to say it is kinda nice pulling all this apart and not having coolant dripping everywhere. I have to admire the simplicity of air cooled engines.

We are at a stop for now until I get a valve spring compressor. The one I have doesn’t work, need the big c-clamp type.

 

[rusty ol ranger]

My Polaris 500 sportsman (also a 4stroke single cylinder) was burning oil like a bitch. (Like 1/2 qt in 10 miles bad), but ran good and didnt have any power loss.

Cylinder walls and everything looked fine. But i replaced the jug, piston, and rings because i was at a total loss. Now it dont lose a drop.

What im saying is it could very well look fine on visual inspection but not be.

...and atleast in the case of my quad...a compression test was worthless because it uses a decompression lever for starting. Not sure on your kids bike.

 

[Blmpkn]

I thought so, the parts manual calls for one and I’ve never worked on an engine that called for silicone for a head gasket.

I knew it was 4-stroke, no premix, that definitely wasn’t the issue.

I have to say it is kinda nice pulling all this apart and not having coolant dripping everywhere. I have to admire the simplicity of air cooled engines.

We are at a stop for now until I get a valve spring compressor. The one I have doesn’t work, need the big c-clamp type.

Those springs aren't light enough where you can't just squish em down for removal with your thumbs?

 

[bilbo]

That's what I thought was weird, other than the unpredictable chinese carb it ran real well. The combustion chamber, valves, and plug were all pretty coked up though.

I ordered the rings as well as a bunch of other parts through Babbitt's. We'll see if/when they show up. I've never ordered through them before. The local dealer said some of the items on my list were no longer available, but Babbitt's claimed they were. Between valve seals, gaskets, and rings I don't know of anything else that could be letting oil in the combustion chamber.

 

[bilbo]

Those springs aren't light enough where you can't just squish em down for removal with your thumbs?

I never even thought of that, maybe. I just assumed they would require a compressor as I've always had to in the past. I'm going to try that when I get a chance.

 

[RonD]

Getting the keepers to release isn't the hard part...................
Holding spring compressed to put them back in is the hard part

 

[Blmpkn]

I've replaced stock springs on a predator 212cc with ones that wouldn't float at 9200rpm with my thumbs.. I might have had some help getting the retainers back in but it was doable

 

[scotts90ranger]

One of those screwdriver things for drum brake springs works decent on that style valve spring, or maybe grab the valve cap with needle nose vise grips and push... I think I did similar with my 350X when I redid it...

 

[SenorNoob]

Babbitt's is pretty good. I try to buy from them every so often just because of how much I use their diagrams to cross-reference parts.

That's how I figured out a carburetor for a 85 XR350R would work on my 78 XL350. With a pod filter, didn't even need to change the jets...

 

[gaz]

@bilbo ,
Worn valve guides can also bleed oil into the combustion chamber.

 

[bilbo]

While taking things apart one of the exhaust bolts broke in the head. It got a daily penetrating oil treatment over the past few days. I welded a nut on it today and tried to take it off, and the bold just broke further in.

Drilling it will kind of suck as it’s at a wonky angle, but I guess that’s the next step. For my next trick I’ll break an extractor off in there!

 

[RonD]

Get a few reverse drill bits, usually the bolt will start unscrewing from the heat and vibration and in any case you still end up with a hole for an extractor