1981 Yamaha G1-A2 With Engine Noise

1YAMAGUY

Cartaholic
Just saw the video...another thought would be that there should be a key in the crank to pulley, could it be worn for some reason. It appeared that the piston was responding to what appeared to be to your movement. Sort of hard to tell but there should with out a doubt some sigh of wear.,,,Somewhere!
Hand hold the crank n see if there is slop trying to slightly rotate the pulley.
 

Cisgww

Member
Here are 3 readings of axial play of the small end of the connecting rod. The dial says 1-1000 IN. Do these 3 average .058” or is it .58”? I’ve got the tools and ability to use them, just need help with the interpreting the results.
The service manual says max play is .79”
Service manual has a typo. Max axial play is 2.0mm or .079”

I calculate my average reading to be .058” and is within tolerance. Correct?
 

Cisgww

Member
Here is clutch side after removing primary drive sheath. Much oily mess on oil pump drive gear cover, but not on oil seal. Seal appears in good shape relative to others seen online. Crank bearing looks good, clean and with no play
 

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Cisgww

Member
Here is fan side oil seal and crank bearing. It was dirty but not oily. Bearing is clean with no play.
 

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Cisgww

Member
Just saw the video...another thought would be that there should be a key in the crank to pulley, could it be worn for some reason. It appeared that the piston was responding to what appeared to be to your movement. Sort of hard to tell but there should with out a doubt some sigh of wear.,,,Somewhere!
Hand hold the crank n see if there is slop trying to slightly rotate the pulley.
Flywheel/fan was tight and key in good condition. No play from that. Suspected connecting rod/bearing play but other posts here show I am within tolerance for wear.
Now Leaning toward piston skirt slop.
With cylinder head off, noise was present when rotating crank (quickly) in both directions. When I applied slight pressure to top of piston with my finger, same rotation had no noise.
 

Cisgww

Member
The clearance at the thrust washer on big end of connecting rod is .019.
Service manual says .010-.030 is acceptable

Machine shop measured cylinder at top where rings seat at 2.68. Bore at bottom of cylinder was 6.677. Piston measured near bottom of skirt at 2.675. Both bore and taper are out of tolerance, as is piston wear. He suggested boring oversize .02”/.5mm. He said he had no issues with aftermarket pistons, but I have a lead on NOS piston and rings by Yamaha

If bottom end bearings are in good condition and within tolerance (connecting rod axial play and thrust bearing clearance), would you leave well enough alone, or go the extra mile and replace the crank bearings and big end rod bearing/crank journal? While it deserves a new bottom end after 39 years of use, is it worth the effort and expense.
 

Cisgww

Member
Was cleaning the crankcase in the parts washer and noticed the cage had failed in the crank bearing on the fan end. I have read much about replacing seals, but no mention to inspect crank bearing. Glad I found it.
Split the crankcase and confirmed complete lack of cage within the crankcase bearing! Note the wear mark on the crank web where the pieces of the failed bearing cage entered the crankcase.
Now I ask, should crank be split and put in a new rod bearing too?
 

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Cisgww

Member
Here is fan side oil seal and crank bearing. It was dirty but not oily. Bearing is clean with no play.
UPDATE:
Look closer at the fan side bearing after seal was removed. Even in the picture posted above you will note bearing is no good as the bearing cage has disintegrated. I didn't notice it until I was cleaning crank case. Anyone changing seals needs to look closer at the condition of the bearing. While I felt no play or grinding in the bearing, it had failed and needs replacing. Here it is after splitting the crankcase and pulling the bearing off the crankshaft.

IMG_6127.JPG
 

Cisgww

Member
for 1981 G1
I am trying to source crankshaft bearings and seals locally...or zoro. Can anyone confirm or provide brand/part # and source, especially for the oil seals?
Crankshaft bearing clutch side Yamaha 93303-30630-00 is (Koyo) 6306/C3 available on Zoro for $8.61
Crankshaft oil seal clutch side Yamaha 93102-30188-00 is FPJ-30 72 8 but I can't find a source/cross reference
Crankshaft bearing fan side Yamaha 93303-20622-00 is (Koyo) 6206/C3 available on Zoro for $5.81
Crankshaft oil seal fan side Yamaha 93102-30128-00 is FPJ-30 48 8 but I can't find a source/cross reference. Maybe a Timken 3945 on Zoro for $8.69?
 

Cisgww

Member
1981 G1
Anyone know the diameter of crankshaft pin?
Trying to buy local: need specs on needle bearings for wrist pin and crank end of connecting rod.
 

Cisgww

Member
Here is my final measure of connecting rod axial play. Service manual says it shouldn't exceed .079". I get about .060". I also measure connecting rod big end side clearance of .019 which is within tolerance of .030 maximum. As I don't have a press, my machine shop not able or interested, and measurements of wear don't exceed tolerances...I won't replace the big end connecting rod bearing. Here is video for future reference and feedback.

 

Cisgww

Member
Source of engine noise found. Piston/cylinder worn beyond tolerance AND crank bearing on fan side was crap...the nylon cage was completely gone!

Note to others: when changing crankcase seals, look closely at the bearing behind it! I didn't notice bearing needed replacing until I was cleaning crankcase in parts washer.
IMG_6127.JPG
 

Cisgww

Member
Here is fan side oil seal and crank bearing. It was dirty but not oily. Bearing is clean with no play.
zoom in on picture of fanside with oil seal removed and you will see the nylon bearing cage is completely gone!
When changing seals, inspect the bearing closely. I didn't notice this until days later upon further cleaning and disassembly

IMG_5991.JPG
 
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