Rebuild project need help!

[Robgerl]

I’m in the middle of a rebuild project that I started a decade ago and never finished. Working on a 2004 ninja 250. The project started with replacing the cam chain because it wore out after 30k miles and I was not going to pay shop labor. I have exhausted all of my bike knowledge and need your help!

Current problem: engine will not fire up and compression is reading 30psi cylinder 1, and 60psi cylinder two. This is the same reading I got before tearing apart engine and replacing gaskets and cleaning valves. Not even with starter fluid sprayed straight into the intake bypassing carbs

Here is what I have done so far:
Entire engine was disassembled and cleaned thoroughly with ultrasonic cleaner
Valves removed and cleaned+ polished. Gave them some grinding compound and re-set them in position so each has a good seal.
New head bolts and gaskets
Rebuilt starter motor
New battery
Ngk iridium spark plugs
Cleaned carbs

Bike mods:
Six sigma stage 3 jet kit
K&n high flow air pod
Cobra F1r slip on exhaust

Sparks good- tested against engine head
Gas is good- same premium gas I use in my Ducati’s
Compression- bad

[DannoXYZ]

Hi Rob, welcome to Ninjette!

Aside from replacing cam chain, did you have any troubleshooting plan for low-compression while you had engine apart? Common causes would be:

1. worn-rings
2. worn valves & seats
3. or mis-timed cams.

Let’s rule out #3 since you’ve replaced chain, so timing would be done on re-assembly.

That leaves #1&2. Did you measure valve’s contact ring width while they were out? Lapping valves typically increases contact-width and lowers contact pressure, leading to lower sealing. Usually needs to have top-cut on seats done at same time to reduce width of 45-degree contact ring. Do you have any photos of valves and seats?

Ring wear or damage also very likely.

At this point, you may need to disassemble engine again to replace rings and/or do complete valve-job. Do leakdown test next to determine how much compression is leaking past rings vs. valves.

[Robgerl]

Hi Danno thanks for the welcome and your response. Yes I did lap the valves while it was apart and replaced gaskets. I did not replace the piston rings because my friend and I had too much beer and settled for good enough. Big mistake. I do have rings on hand and will tear apart to replace. Timing is good and valves look to be good and seat well. It has to be the rings. Some pictures of valves attached.

[Triple Jim]

The old trick of squirting a teaspoon of oil in through the sparkplug hole and re-testing compression will verify that the rings are the problem.

[Robgerl]

I’ve never heard of that test(I’m also not a mechanic). If I add oil and re-test I should see higher compression correct?

[DannoXYZ]

Yes and no on oil-squirt.

IF compression increases significantly (say.. to 130–150psi), THEN rings are issue.
but IF compression doesn’t go up significantly, THEN issue is valves aren’t sealing.

Probably combination of both. Leakdown test will give you more concrete data.

Photos shows exhaust seats (except for one) are extremely worn out with 2.5-3.5mm contact. Intake seats are over service-limit at ~2mm. Definitely needs top-cut on all of them. But nowadays with 3D cutters, you can do all three angles at once in single pass. Might as well do complete valve-job. Target 0.5mm on intake and 0.7mm on the exhaust.

[DannoXYZ]

How many miles on this bike?

Due to steel liners, which does wear away faster than Nikasi-coated liners, bores will most likely need light honing and crosshatching. Otherwise, new rings will never break-in and seal properly. Leading to lots of oil-burning, smoking and poor power.

[SibSerge]

A couple of notes on measuring the pressure, you might already know but I would mention it anyways.
1. Make sure the air path is not obstructed (no carbs or fully open throttle) when you take the measurements.
2. Depending on the hose adapter you use on you measurement gauge the rubber oring might not sit properly and will let the air past resulting in a low reading. I cover it with a bit of copper antiseize lubricant to help it sit properly.

[SibSerge]

Back in 80ies when I was watching my grandpa lapping the valves of his Ural I noticed he used kerosene to confirm that there was no leak before putting the head back. I think kerosene has great penetrating capabilities and would be a great and cheap way to find leaks.