Drz400 head !

What's up guys , my Drz just rolled of 36,000 miles . I was riding the other day and the motor had took a shit . Got home tore it apart to find that a piece of the valve guide in the head had broke off , went down in the cylinder and caused carnage to the piston and the head . I got a new head and big bore kit from a friend. Installed it go to start it , it started for 5 sec and then locked up on me.

I took the valve cover off and noticed that the intake camshaft had spun on the cam gear. Weird! Had another set of cams I threw in . Timed it correctly , put it back together and started it . Same thing ran for a few sec and locked up. Took the valve cover off , cams out , and the intake cam was all scored up and the journal where the cam rides on the head was all scratched and rough. I have no idea what caused this . And on top of that there was coolant in my oil . Bad head gasket ?!?! Still doesn't explain why cam spun on the gear , and then second set of cams just ate the journal and ruined the head .

Any input ?

Did you make sure the head wasn't warped? Didn't reuse the head gasket? Welch plugs intact? Sounds to me like you weren't getting oil flow to the head

Did you make sure the head wasn't warped? Didn't reuse the head gasket? Welch plugs intact? Sounds to me like you weren't getting oil flow to the head

I don't think it was warped . Welch plugs were there . And it happened within 4 seconds of motor being started

Over torquing the camshaft cap screws? With a torque spec of only 7 ft/lbs, it would be quite easy to "clamp" the camshaft in the journals by cranking these screws down tightly. Lack of assembly lube?

Either ran it low on oil scored the cam gears slowly till they cooked now with the combination of maybe overnitighting

And did you use assemble lube and all that stuff just sounds like an extreme lack of oil..maybe lubrication system isn't working anymore

1)  a piece of the valve guide in the head had broke off , went down in the cylinder and caused carnage to the piston and the head .

 

2) I got a new head and big bore kit from a friend. Installed it go to start it , it started for 5 sec and then locked up on me.

3) I took the valve cover off and noticed that the intake camshaft had spun on the cam gear. Weird!

 

4) Had another set of cams I threw in . Timed it correctly , put it back together and started it . Same thing

 

5) ran for a few sec and locked up.

 

6) the intake cam was all scored up and the journal where the cam rides on the head was all scratched and rough. I have no idea what caused this .

 

7) And on top of that there was coolant in my oil . Bad head gasket ?!?!

 

8) Still doesn't explain why cam spun on the gear , and then second set of cams just ate the journal and ruined the head .

Any input ?

 

1) over heated from lack of lubrication ? valve guides usually don't break without an oiling issue. 

 

2) oiling issue, or used the wrong cam caps. the cam caps are line bored for each head, and only that head. if you swap intake vs exhaust, you'll have problems. if you swap from head A to head B you'll have problems. if you have an oiling problem... well, ditto. 

 

3) that sounds about right for an oiling issue AND a cam cap issue. too much force on the cam will bind it, and spin the cog on the cam. 

 

4/5) ditto 3

 

6) ditto 3, but the scoring means that it moved momentarily, heated up fro mthe lack of oil and/or over torqued/incorrect cam caps, and then seized. that's why it has marks on it. 

 

7) coolant in oil was likely present before the other issues, and part of the bad head problems. the spraying of coolant into the combustion chamber means the combustion pressures can rise much higher than normal, and that some parts may be cooled while others are hot. different expansion rates = bad for engine parts, not to mention water isn't a good lubricator. if it steam cleaned the valve/valve guide, there's an issue and you're seeing the results. 

 

8) see 2, 3 and 6.

 

 

A base gasket can be reused, sometimes. Depends on it's condition after the cylinder is removed. If it's greased before installation, maybe it will be ok. If it's copper sprayed, it will likely come apart. The head gasket has compression zones/rings that mean it should only be used once. Before installing a head (or any internal piece) always make sure it's surfaces are completely free and clean of dust/dirt/sand/grime/etc and NOT dry. With the exception of a new piston/rings, everything else should have either a coating of oil or bathed in oil. Assembly lube is good for brand new parts, used parts, or just... holding things together at odd angles until it's all done. It's not required though, engine oil is fine. One spec of trash in the cam journals will kill a journal, and then possisbly the cams, very quickly. 

The only thing I didn't do was put oil on the cams before install. But the head was used and was oily before I put it in and didn't think that I needed to lol. F*** me right ?

When the bike broke initially , from the valve guide breaking off , the bike ran phenomenal all season no issues at all . So I'm thinking it was just old age lol. The bike had 36,000 miles on it

This is why I initially rebuilt the top end and got a new head .

AB3E370D-5F99-4B7C-9121-C8C14405BD52.jpg

How long do you suggest for run in period after a full top end rebuild ?

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