Bad News

[Bribird]

Sure Roller bearins are more reliable, but also more expensive to produce. A vast majority of the internal combustion motors on the planet have plain bearings and survive quite nicely. I wouldn't necessarilly blame this on the type of bearing used.

What baffles me is that it appears to be correctly built and there isn't an identifiable reason for this failure.

What I am leaning towards, at least in my thought process, is a misplaced bearing. The bearing selection for these motors is easy to get mixed up during assembly.

My motor has a BBB BBB case. I have 1 "A" journal and 5 "B" journals on the crankshaft. Which means my bearings for the crank are 1 black and 5 brown. My crank and rod numbers are.... 1:1 which is a green bearing, and 2:2 which is a brown bearing.... so I got 3 browns and 1 green for the con rods. If You were to lets say put a brown(1.492-1.496mm) bearing in a green(1.484-1.488mm) spot... well you could have a problem like this, which would like much like an oil starved bearing. I could see where someone could just easily get mixed up and make an opps. All the bearing look the same except for a tiny splash of paint on the edge.

Just a thought.

[Don-lo]

Your oil pressure took a huge drop when that bearing opened up, and yet the other 3 assemblies were fine after extended running. Those oil ports are also so big as to be very difficult to plug. Did you plastigage all around the bearing before assembly? One poster theorized possible warping due to previous overheating, but I would guess that to be unlikely without major overheating (actual bearing failure). A change in bearing design casts a cloud over the whole thing. Did you use assembly lube when it was put together?

[TheCafeKid]

Sure Roller bearins are more reliable, but also more expensive to produce. A vast majority of the internal combustion motors on the planet have plain bearings and survive quite nicely. I wouldn't necessarilly blame this on the type of bearing used.

What baffles me is that it appears to be correctly built and there isn't an identifiable reason for this failure.

It has nothing IMO to do with the use of plain or roller bearings...it has, IMO, everything to do with the mapping of the oil delivery passages. There is one undeniable truth across the board. These failures dont seem to happen as often, if at all, to the low pressure RBC motors. Why is that? Besides the use of roller bearings and low pressure systems, what is the main design difference? Delivery set up...

[reddirtrider]

It has nothing IMO to do with the use of plain or roller bearings...it has, IMO, everything to do with the mapping of the oil delivery passages. There is one undeniable truth across the board. These failures dont seem to happen as often, if at all, to the low pressure RBC motors. Why is that? Besides the use of roller bearings and low pressure systems, what is the main design difference? Delivery set up...

If it was due to the mapping of the oil delivery system, don't you think this failure would be more prevailant? The factory produced untold numbers of these motors and I've yet to hear of any real design flaws.

[TheCafeKid]

Its pretty prevelant. I have TWO 750 PBC motors at the house that are blown up from oil flow problems. I have replaced, and have the carcass of a 550 PBC motor in my shop that blew a conrod bearing (coincidentally number 3) from oil flow problems (in this case i believe it was low on oil and wasnt dealt with) and if you look at people on the board who've blown up or are repairing blown up motors, they are almost ALL the 16 valve plain bearing crank motors. Im not saying i know exactly WHY, but in looking at the differences in mapping, there are some things that stick out that make me wonder WHY they were mapped that way...and then of course the fact that alot of these motors blow up makes me question things even more..the 80-82 750 motors are notorious for doing this. The design change in 83 seemed to quell that problem, but untill then, most of them were only a matter of time, or a owner that didnt pay attention away from giving up the ghost. Again, im no engineer, nor did i have any hand in designing these motors, but its pretty glaring that they are the most UN-reliable of the GS motors... the 650 was a bit of a bastard in design, as it was the 8v head with a PBC and high pressure oil system..

[reddirtrider]

Its pretty prevelant. I have TWO 750 PBC motors at the house that are blown up from oil flow problems. I have replaced, and have the carcass of a 550 PBC motor in my shop that blew a conrod bearing (coincidentally number 3) from oil flow problems (in this case i believe it was low on oil and wasnt dealt with) and if you look at people on the board who've blown up or are repairing blown up motors, they are almost ALL the 16 valve plain bearing crank motors. Im not saying i know exactly WHY, but in looking at the differences in mapping, there are some things that stick out that make me wonder WHY they were mapped that way...and then of course the fact that alot of these motors blow up makes me question things even more..

I might suggest that these are nearly 30 year old motors that you probably don't know their history and how they were maintained or treated.

[TheCafeKid]

GOod point, except that i have 12 bikes sitting in my property at the moment, ranging in years, and models, all of them have different motors, questionable maintenence records, and the only ones that seem to have THIS problem are the PBC motors. Im not saying that they are crap motors, well, not ALL of them were crap motors (you couldnt GIVE me an 80-82 750) im jsut saying that THIS problem seems to crop up MOST in THESE motors...WHY?? I mean, its just as prevelant to ME, having read pleanty on this board, as the mid 81-84 rear spline problems in the big shaft drive bikes? Are you going to tell me now that it wasnt a design flaw there? and that i dont know the maintanence history of these bikes? Im just saying that Old man Zook wasnt infalable, and they were pretty quick to clean up a mess with the 750 design when they switched to the 83 models. Zook wouldnt change anything if they didnt HAVE to, why would they have changed the 750 design in 83 if it was working??

[reddirtrider]

GOod point, except that i have 12 bikes sitting in my property at the moment, ranging in years, and models, all of them have different motors, questionable maintenence records, and the only ones that seem to have THIS problem are the PBC motors. Im not saying that they are crap motors, well, not ALL of them were crap motors (you couldnt GIVE me an 80-82 750) im jsut saying that THIS problem seems to crop up MOST in THESE motors...WHY??

I'd say you're one data point. There may be someone out there with a dozen 750's and has never seen this problem, I don't know.

If there was an oil delivery problem from the factory, why haven't we heard of it? It's a very competitive world out there. Why hasn't someone brought this up before in order to slam Suzuki and boost the sales of their motorcycles.

Maybe you just have bad luck, then again maybe you're right, but we'd need a lot more data points and complete histories of the bike in question.

[TheCafeKid]

I'd say you're one data point. There may be someone out there with a dozen 750's and has never seen this problem, I don't know.

If there was an oil delivery problem from the factory, why haven't we heard of it? It's a very competitive world out there. Why hasn't someone brought this up before in order to slam Suzuki and boost the sales of their motorcycles.

Maybe you just have bad luck, then again maybe you're right, but we'd need a lot more data points and complete histories of the bike in question.

oh they werent motors *I* blew. Again, I wouldnt own one personally, but they are motors from various people that ive either aquired, or repaird, or attempted to anyway, that im talking about... But, I digress, you are right in your last point...But on your second point, the one i bold faced, Zook let the rear spline issue go for how many years? before doing something about it? Its been WELL documented here, but id never heard of it prior to owning one. *MY* point is, just because it wasnt made an issue, doesnt mean there wasnt one to begin with...

[Dave_17954]

I blew air through the oil hole on the crank bearing next to the 3#conrod bearing and there was a good amount of air coimg through the conrod holes so nothing plugged in there. I have noticed my oil is real uhmmmm thick i would call it not sludgey if thats a word but almost a gooey consistency down in the oil pan or at least very thick. I was using castrol gtx 10w40 oil in it. i've noticed also the oil filter has this same gooey type feel to it. I"m going to give everything a good cleaning in my wash tank and if I can get me another good used crank and rod I'll probably replace all the bearings rod and crank just to be safe and maybe go to a different type oil. This was the first time ive used castrol gtx. I normally run penzoil.

[reddirtrider]

Your use of the therm PBC and RBC has me confused. I was assuming you were refering to plain vs. roller bearings. Now that I've read your posts again - is this some acronym refering to the 80-82 750's - a specific model year?

[TheCafeKid]

No, you are correct, PBC is plain bearing crank, and so on. However, the pre 80 models of the 750 used 8v heads and roller cranks, the 80-82 used 16v heads and plain cranks, and 83 did as well, but they were a COMPLETE redesign from the 80-82 model...


Dave, Try Rotella bro. 15/40, i dont use anything else, never will. Modern oils have a crap load of detergents and additives in them that are no good for these old girls. Diesel oil is where its AT!

[Dave_17954]

I looked right at the rotella when i was at wally world. The cycle repair guy up the road says he's used nothing but castrol gtx in all his service work and recommended it. next time it will be rotella.

[Bribird]

Hey Dave, that kinda looks like the moly paste after the first oil change. I personally dont like castrol gtx but I doubt that was your failure. Check the paint on your bearings and make sure they all match(ed) up to the crank numbers. 2 yellow and 2 brown on your motor. the 2 and 3 cylinders should have yellow bearings.... right?

[reddirtrider]

No, you are correct, PBC is plain bearing crank, and so on. However, the pre 80 models of the 750 used 8v heads and roller cranks, the 80-82 used 16v heads and plain cranks, and 83 did as well, but they were a COMPLETE redesign from the 80-82 model...


Dave, Try Rotella bro. 15/40, i dont use anything else, never will. Modern oils have a crap load of detergents and additives in them that are no good for these old girls. Diesel oil is where its AT!

Ok, my thoughts were centered around PBC's in general, while you were refering to a specific set of years and model. It appears we were talking about 2 different issues.

You may be right about the 80-82 750's. I don't own any and I usually don't get involved in threads unless they interest me, so in general a lot of them go by without notice.