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The rebuild of great disappointment.

  • Thread starter Thread starter Willmrx
  • Start date Start date
W

Willmrx

Guest
After 3 1/2 years of waiting until I got all of the parts I needed to rebuild my 1981 GS650G engine, ended not so well. I rebuilt my 1982 GS650G almost two years ago and have put about 10,000 miles on it with no problems. However, I was not as lucky with the 1981. With about 160 miles on it, I noticed the oil light was pulsing at idle, which was set low at 800 rpms (I had not yet adjusted it). I replaced the oil and filter and all was well, until about the 350 mile mark, I notice it was getting noisy from time to time. So I made up a oil pressure gauge that I could see when I was driving. The oil psi was not stable, it went from 70 ish to about 10 psi. I replaced the (BULLETPROOF) oil pump, (just because I had a known good one), the oil regulator and still had the same issue :(. I removed the engine and have split the case. I have yet to find anything out of place, no pinched orings, all 3 brass oil restrictors in place and seated correctly with orings intact, base gasket in perfect shape. I am think now that there is possibly some leakage in the head? The other thing I was thinking, is that I retaped all of the holes in both upper and lower cases, and head. I thought that I may have breached the casting in some way, causing a loss of oil psi. At this point, I am at a dead end! Any ideas on what else cause a loss of oil psi? I posted the photos of the damage in my photo album .

Thanks!

Will
 
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retapping the crankcase threads will not hurt at all unless you retapped them larger than standard, then you could possibly break through to oil passages or the open air.

shell bearing cranks create their own oil pressure to a certain extent by the oil being forced in and out of the shell bearings, as well as the oil pump to push the oil around.

as all the crank bearings are worn i am guessing you rebuilt the engine with the wrong size shell bearings on the mains and the big ends.
 
Willmrx said:
So I made up a oil pressure gauge that I could see when I was driving. The oil psi was not stable, it went from 70 ish to about 10 psi. I replaced the (BULLETPROOF) oil pump, (just because I had a known good one), the oil regulator and still had the same issue :(.
Click to expand...

Just something to cross off the list: Are you certain the oil pressure gauge is working correctly?

Where did you hook it up to?
 
Is that threebond on the mating surfaces next to the bearing shells??
When you torque it down, where do you think the excess is going to go? IMO it will go on the crank and bearing and into the oil passages.
Are your oil pump drive components intact and in good shape? Did you plastic gauge the clearances before assembly?
 
I connected the pressure gauge to the oil filter cover plug, and use a hose going up to a psi gauge I taped to the dash. I trust the gauge. I did not plastic gauge all of the bearings, just three of the cranks and two of the conrods and all looked good. The reason I did not do all the bearings is, they were only two sizes. I had all #1 conrods and #2 on the crank and I had one #A and the rest were #B the crank. The Case was all #B. I retaped the holes with the same size threads. For the Yamaha bound getting into the bearings, I have to look closer to see if there was a too much applied.
BTW Thanks for everyones help!
Will
 
Personally I'd try another oil plump, or at leat see if the current housing is worn.

- boingk
 
Okay! I now have almost 600 miles on the second engine rebuild, with no issues! I could not find a single thing wrong with the assembly of the first rebuild, nothing. What I remember was, I had hand cranked the engine over several times without plugs, to get the oil system primed before I attempted to started it. When it started the bike went right up to 2000 rpm plus, for about 15 20 seconds before I could turn the idle down. That is when I believe the damage occurred.
On the second rebuild, I put a electric drill to the crank, and turned it until oil was coming out over the cams. Which took a longer period of time than I expected, like a minute and a half. So what I think I did wrong was, I let the rpms get way too high and I did not get the engine oil system primed properly. The result was I damage the conrod bearings and then the low oil pressure damaged the rest of the bearings. Oh well, another lesson learned from The School of Hard Knocks.
 
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