2003 4Stroke issues, shoud have just bought a new motor!!!!!!

[95GeeTee]

Man where to begin, this motor is messed up and has just about cost me as much or close to buying a new one. Big mistake, I should have but you never know. One of the mechanics (a certified Yamaha guy) said this was the worst motor Yamaha ever made and they changed the design quick, he declined to work on it. Anyways here is my issues:

Yamaha 2003 T60TLRB (4Stroke,60HP)
1. multiple back fires in intake up to around 3000-4000rpm
2. motor shakes bad at idle but smooths out around 1500 rpm
3. Motor runs fine full blast, but shakes the crap out of you and back fires in low rpms


My diagnostics and what has been done
1. The 4 carbs on this motor have been rebuilt several times, no difference each time, they were resynced also afterwards. Every repair guy thinks it is a carb problem but that doesn't fix it.
2. The head has been rebuilt, new valve seals, resurfaced, new head gasket, etc.
3. Cylinder 3 has low compression (74 I think it was) when compression test is run with throttle closed. Weird thing is with throttle open compression test is fine, 175 or 200 cant remember but it was good and equal across when we did the test with open throttle.
4. BLOWBY AT LOW RPM, from idle to 2000 rpms there is blowby, pulled the hose off the exit port on the valve cover to find this out. 2000-2500 it goes away and none at all at 2500 and higher.


I have changed things out like plugs, coils, etc.

What gets me is the motor runs great a high RPMs but at low RPM its a wobbling, backfiring mess.

My guess is piston rings on cylinder 3, but why does it run good at higher rpms? No smoke from exhaust either.

Just wanted to get a second opinion before I tair this apart myself. Thanks and I really do appreciate any info.

[boscoe99]

Compression test should be done with the throttle wide open. Motor hot.

If the compression test indicates something is not right with cylinder #3 (low compression vis a vis the other cylinders) it is time to do a differential pressure test. That test will indicate which portions of the combustion chamber are not sealing as they should be. Based on the blow by you are seeing it will probably be the piston rings that are not sealing.

Your mechanic is mistaken. Or an idiot. There is nothing different about the basic design of the F60/T60 than any other Yamaha four cylinder inline model.

If the motor has a mechanical problem (say low compression due to worn rings, valves, gasket, etc.) then all of the carburetor cleaning in the world will not fix that problem. The motor has to be fixed mechanically first. Then and only then can you proceed to tweek the carburetors and/or make other adjustments.

[99yam40]

do you call replacing valve seals and resurfacing the head rebuilding a head?

why was the head so called rebuilt?

most all of 4 stroke motors will push air out of the crankcase while pistons go in and out displacing volume.
do the Leak down testing to see if rings are stuck,broke, or something else is a problem with cylinder sealing

[99yam40]

Compression test should be done with the throttle wide open. Motor hot.

If the compression test indicates something is not right with cylinder #3 (low compression vis a vis the other cylinders) it is time to do a differential pressure test. That test will indicate which portions of the combustion chamber are not sealing as they should be. Based on the blow by you are seeing it will probably be the piston rings that are not sealing.

Your mechanic is mistaken. Or an idiot. There is nothing different about the basic design of the F60/T60 than any other Yamaha four cylinder inline model.

If the motor has a mechanical problem (say low compression due to worn rings, valves, gasket, etc.) then all of the carburetor cleaning in the world will NOT fix that problem. The motor has to be fixed mechanically first. Then and only then can you proceed to tweek the carburetors and/or make other adjustments.

fixed it for you

[boscoe99]

fixed it for you

OOPs on my part.

Thanks.

[TownsendsFJR1300]

Just for S&G's, check the crank to cam's timing belt to make sure its dead on (all marks line up).

Also check valve clearances on all cylinders while at TDC, COMPRESSION stoke.

[95GeeTee]

do you call replacing valve seals and resurfacing the head rebuilding a head?

why was the head so called rebuilt?

most all of 4 stroke motors will push air out of the crankcase while pistons go in and out displacing volume.
do the Leak down testing to see if rings are stuck,broke, or something else is a problem with cylinder sealing

Welding around combustion chamber, resurfaced, complete disassembly, boiled and blasted, new seals, new anodes, springs tested and overall inspection.

I called it rebuild, you call it what you want. Thanks.

[ausnoelm]

So, some welding has been done on the motor?

[95GeeTee]

So, some welding has been done on the motor?

On the surface of the head.

From corrosion there was a slight dip between one of the water jackets and combustion chamber. This was welded and resurfaced. You can do this with aluminum, but not sure on cast steal heads.

Here is a pic. you can see the roughness between the water jacket and the combustion chamber on the surface of the head. I dont have an after pic but it looked like new when finished. I thought this was the problem because it apparently looked like compression was getting through head gasket/head into water jacket, but after this repair there was no difference from before.

[ausnoelm]

Leaks between cylinders can cause back firing (kind of like a burnt valve) what CAN happen is, an adjacent cylinder firs, the gas leaks to the next cylinder that just happens to have a valve open, and you have what appears to be a back fire. Not saying this is your issue, but it has happened before.

[rodbolt17]

do a leak down test.

a compression test is a teat on a boar hog on that motor.

IF and ONLY if the cylinders can seal.
find and fix the valve timing OR fuel issue.

but if the leakdown FAILS no amount of fixing will make it run correctly UNTIL the leak down passes.
compression test WILL NOT and CANNOT find small leakage in a valve,ring OR head gasket.

the leakdown will and it will tell you ECZACHARY what the ell is leaking in the so called sealed cyl.

that's why a pression test on a 4 stroke is a teat on a hog.

that and I am lazy and at 100 buck/hr I can do a leakdown in 1/2 the time you can do a pression test .

on your motor the flywheel is already indexed.
bring it up to TDC. leaktest #1.
if it fails like miserably simply rotate the crank 360* and do it again.

the simply follow the fireing order 1 3 4 2.

done.