I'm new to the forum but can't wait to build my xs400.I did a compression test and got 121-124 psi dry but I notice blue smoke from the left side as it warmed up.Should I try new rings or just run it for now.Is there bigger piston and rings kits like the xs650's?
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81 xs400 rings and pistons.
- Thread starter McSween
- Start date
How did you do the compression test? Just hook the tool up and kick it over? Cold, warm, oil, throttle?
120 is OK but it is on the lower end. If the engine idles its probably OK. Ive gotten big differences in my compression numbers just by how I performed the test so it helps to know how exactly you did it.
120 is OK but it is on the lower end. If the engine idles its probably OK. Ive gotten big differences in my compression numbers just by how I performed the test so it helps to know how exactly you did it.
Make sure your valves are adjusted to spec. With the motor cold do a compression test with the throttle wide open. A good motor should be 150+psi. 125 is the bottom end. If you put a little oil in each cylinder and do the test again and get much better numbers, your rings are bad. If there's no change, your valve seats are bad.
It was cold with throttle wide open and used starter.I didn't try any oil but will,how much oil to use? Thanks for your help.
How much oil Chris? Thanks for your help.
Ok thanks,I will try that when I'm back home.
Thanks Chris,I do have another motor but only got 90 psi in both cylinders kicking in over while the engine was sitting on my floor.Time to rebuild I guess.
Yeap thats right... Prices are high and you wont find them any lower.. You may be able to get away with a simple rehone and new rings. That would be your cheapest option.
When you talk about new pistons, youre in the $500 range easily for all the work, even more if you dont do it yourself
I probably put over $1200 America dollars into my engine just to hear it start up again, mind you I bought my bike with a seized engine.
When you talk about new pistons, youre in the $500 range easily for all the work, even more if you dont do it yourself
I probably put over $1200 America dollars into my engine just to hear it start up again, mind you I bought my bike with a seized engine.
How many motors do you want running? The valve job on the 150/125psi motor will be a lot cheaper than anything for the pistons.
As for honing and rings. All depends on how bad the cylinders are. If the stock sizes will no longer work you'll need matched sets of oversized pistons and piston rings.
Hard to find and expensive.
As for honing and rings. All depends on how bad the cylinders are. If the stock sizes will no longer work you'll need matched sets of oversized pistons and piston rings.
Hard to find and expensive.
I just want one motor running and I guess I will tear it apart and have a look,thanks for your help.
If you can feel a lip at the top of the cylinder wall where the rings stop, you need a bore job.. if its just the cylinder walls that are glazed, you can probably get away with a hone and rings. Your local machinist will know. The max clearance is .002” before you need a new bore. My machinist spec’d my new bore job at .003” and said it was OK. He mainly does Harleys though.. my bike runs very strong.
Thanks Mike,I will check it out.
nuke
XS400 Member
I'm currently in the rebore process. So far - 270Euros for pistons, rings and bolts +0.25 (first oversize) and probably around 50Euros for reboring and honing, still waiting the price.
I was low on compression - 9.0 bars (under the limit, but working). Tried with hone and the old rings (bought new from ebay and they didn't fit) and the compression went 7.5 bars.
I was low on compression - 9.0 bars (under the limit, but working). Tried with hone and the old rings (bought new from ebay and they didn't fit) and the compression went 7.5 bars.
