Jump to content

DRZ 400 low compression need ideas

Recommended Posts

Posted (edited)

I picked up a '01 400 kicker last year for $1,100 - a picture is worth a thousand words! I rebuilt the flat side carb and checked the valve clearances, all were within spec. I didnt compression test it at the time. I rode the bike last year several time on trails, also titled it and ripped it on the street a little bit. It ran pretty good for what it is (it never left me stranded) but I noticed it started to run a little choppy toward the end of last year. Fast forward to this year after sitting for several months-- try to start bike, wont start. Put a new plug in and yanked the carb cleaned it, the bike would start for about a second then die. Kick starter felt too easy.

I then compression tested after yanking the manual decomp. Readings were 30-60. When kicking without the plug there didnt seem to be much compression by feel or sound. I then put a couple caps of oil in the cylinder and kicked it/compression tested. It tested around 120 and compression NOTICABLY improved. It started for a couple seconds then died. Compression dropped and kick starter back to "limp". I'm planning to do a leak down test tomorrow but I'm suspecting bad rings, etc.? I'm guessing this bike doesn't have a ton of miles as it was never titled and was a dirt model. I know everyone is going to say get a big bore kit. I'll go that route if I have to replace the cylinder/piston but otherwise I'd like to do this on the cheap! I'm a competent mechanic and have built many engines but its been a while since I've had the top end off a bike.

A few questions:

What else should I try/check before I tear this thing down?

Assuming the piston/cylinder is still in good shape is a cylinder deglaze/rering an option? I read these cylinders cannot be bored. Is this a common fix for this type of problem?

What brand parts should I look for? I see a wide range of parts are available.

With a big bore kit, what ELSE is necessary? Do the cams need to be changed too? I'd prefer to keep the stock valvetrain.

 

 

20180916_183952.jpg

Edited by 68lemans462

Share this post


Link to post
Share on other sites

You can re-ring, or new piston and rings, or if the is cylinder damaged have it replated and new piston & rings, or you can fit a big bore

 

Big bore csn be fitted with no other changes for a power boost...might need a smaller main jet

You cant rebore cylinder as it is a plated bore and so has to be replated if damage, there are no oversize pistions anyway because of this

Share this post


Link to post
Share on other sites

X2 on the above and other than doing a leakdown test, I think the writing is on the wall for bad rings/piston. Check the lower connecting rod for play while you have the piston out as well. I put a Wiseco piston kit in my E and have been happy with it. Also check condition of valves and guides.

Looks like someone titled that bike at some point? I see a rear plate in the picture as well as hybrid street tires and a side view mirror....

Share this post


Link to post
Share on other sites
X2 on the above and other than doing a leakdown test, I think the writing is on the wall for bad rings/piston. Check the lower connecting rod for play while you have the piston out as well. I put a Wiseco piston kit in my E and have been happy with it. Also check condition of valves and guides.
Looks like someone titled that bike at some point? I see a rear plate in the picture as well as hybrid street tires and a side view mirror....
Yes indeed... I am the one who titled it

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×
×
  • Create New...