lubrication problems

[scrambler]

Hey Folks,

This forum looks quite abandoned, so I bring up something that might initiate some discussion

Finally I managed to get the paperwork done on my bike, it took me a couple of months and several rounds to the DMV, but now I`m the legal owner with a pink slip with my name on. So, as the restoration/renewal makes sense now, I`d like to explore around what to expect. My bike is a `73 year with no modifications besides the oil cooler and the automotive filter. I read a couple of articles here and there and I learnt that this year version suffered of oil pressure problems due to the bubbles caused by the balance shaft that yamaha solved by adding a deeper sump to the bike from `74 on. What I don`t understand is, if this engine has a dry sump system, shouldn`t it be free of oil in the sump? And if it`s not, because, say the scavanging is not perfect for some reason, the foamy oil is going to the oil tank anyway, so the bubbles would have time to come out.. Still, at most forums replacing the sump to the deeper version is highly recommended. However, my bike made 35000 miles with the original sump and the engine seems untouched (not much compression left, though). So, what is the general thinking about this? Is it rather the failure of the scavanging that causes the problem when coincides with the shallow sump? In other words, if the scavanging works fine, it does not matter which type of sump I have on the bike? Let me know what you guys think.

Greg     

[jayteenz]

Hi Greg

The forum can be quiet from time to time but it's still worthwhile.

At high rpm the balance weights would whip oil in the sump into a froth, aerating the oil and starving the crank for lubrication which resulted in bearing failure. Top end bearing failure (cams) often occurred to.
A deep sump is must if you want to guarantee reliability (and be able to ride it hard).
I suspect your bike has not been run a high RPM consistently and it may have been spared as a result. Remember, these things don't put out large HP so wide open throttles was the common way to ride them in the early 70's.
In addition, the other problem with early models was the balancer chain would stretch, resulting in the counterweights being out of phase and making the engine run rough. Later models had adjustable chains to take up the slack.

Cheers - JT

[farmrjohn]

Your oil cooler would certainly help prevent the frothing as well by keeping the temperature down. In addition to lower revs/deeper sump, modern oils perform better than the older ones. That could lead to another discussion on "what oil do you use?" Shell Rotella T-6 for me.

[scrambler]

Thanks for the comments, I`m looking forward to seeing inside the engine how the past 35000 miles affected the parts. I have all the documentation from the purchasing of the bike, and apart from a camshaft replacement at about 800 miles in warranty no engine related issues are mentioned. I guess the oil cooler does a huge improvement indeed, because the oil picked up from the sump goes through the tank and the cooler, and only after that it reaches the bearings, so it has a long time to cool down and get rid of the bubbles. But correct me if I`m wrong. 

[bigskyforever]

The oil is cooled prior to returning to sump. Also having the cooler and lines full of oil would assist in longer oil life cycle as you have a greater amount of oil in the system.

[argo1974]

Deep sump and oil cooler weren't standard even on 74" bikes. IMHO, deep sump is overrated, there are TX bikes around > 100.000 km without sump extension but with big oil coolers. Plain bearings inside the engine prefer temperatures between 80 and 100 deg. Celsius, so oil inside oil tank should stay somewhat below these temps. Back then, oil foaming never happened with engine/oil cold, it was always an overheated engine/oil issue.

As goes to oil pressure, feed pressure is only to fill plain bearings with oil. The bearing-journal unit generates its own pressure 100-200x the initial feed pressure. Modern scientific studies show plain bearings can benefit from aerated oil since it thickens the oil inside the bearing. Increased viscosity also means increased load capacity of the oil film. Oil aeration increases with oil temperature and engine speed. E. g. on modern car engines, oil aeration rate at WOT is usually 3-4x aeration rate at idle. The negative, when oil is aerated, its thermal conductivity is reduced. This lowers the oil ability to contribute to engine cooling and to cool down itself. IMHO, TX engine will benefit from oil aeration until the negative effects caused by temperature rise start to dominate. Then, with sharp oil temperature rise and thus viscosity loss (=load capacity loss) a short self-enhancement process will take place resulting in seized crank. Mineral oil upper temperature limit is approx. 160 deg. Celsius. TX conrod/crank bearings are rather small for a 750cc twin, so they don't have much reserve.

[jayteenz]

Argo - very informative thanks.
In relation to your last comment, what oil would you specify for the TX ?
I own a CB750(plain bearings also) and the strong belief is that mineral oils are best for them due to the higher zinc content which is more beneficial to the plain bearings. Perhaps a semi-synthetic is a good compromise ?
Would appreciate your thoughts - JT

[argo1974]

JT, in fact, modern oils are cocktails containing base oil (synthetic or mineral) and additives (up to 30%). So zinc (ZDDP) content rely on particular additive package only and it's more beneficial to areas with high specific pressure like flat tappets of the valvetrain. Today, with zinc replaced with more modern additives, you should rather keep an eye on HTHS > 3.5.

For stock TX engine with oil sump temps up to 320 deg. F at high load/high ambient temperatures, I would suggest 10W-60, 15W-60 or 20W-60 synthetic oil. With deep sump, oil temperatures close to 290 deg. F still remain too high, so oils mentioned above or at least 10W-50, 15W-50 or 20W-50 synthetic oil should be used. For mineral oils, sump temperatures shouldn't rise over 210-220 deg. F, which requires big oil cooler or stock oil cooler + sump extension plate on TX. Then, take at least 20W-50 grade mineral oil, those have higher VI (viscosity index). The reason against 10W-40 or 15w-40 minerals is TX engine's design with high heat cylinder head. In the past, this particular 4 stroke design concept was often used on air cooled engines. The basic idea is to direct as few oil to cylinder head as minimally required for lubrication purposes. Generally a 4 stroke engine transfers approx. 75% of overall heat through cylinder head. So with less oil flowing through high temp cylinder head, oil sump temps could be kept down with no need of external oil cooler. On this kind of engines, you will often see cylinder head warpage, oil seepage and detonation problems. And valvetrain issues/premature wear with mineral oils.

I own over 30 vintage motorcycles both 2 and 4 strokes. At my experience, modern synthetic oils can cure lots of children's diseases present on these vintage engines. Engine mechanical wear limits are often reached 2-4x later.

[scrambler]

Argo, thanks for all your comments, they are indeed very informative. I came across a write up of yours about the modifications of the oil passages and I have a couple of questions, if you read this i`d appreciate if you or anybody else could clarify a couple of things. Your post about the modifications is here: advrider.com/index.php?threads/tx750-early-style-cases-oil-passages-mod.911157/

I have a 73 bike on which I possibly will do the same modifications because they seem to be straightforward and I wanna keep the engine because of the matching numbers. I have not started stripping down the engine yet, but I bought an engine for parts and I took it apart. The first thing that is unclear is what you meant by magnetic oil filter cavity, since I could not find anything magnetic here. Honestly I don`t really understand the function of this part at all. It seems something like a centrifugal filter but it`s different, and I don`t get it even when I look all the types of the part diagrams.

The other thing that is puzzling me is that you say that you unplugged and then replugged the channels marked red that open to the magnetic filter cavity. Interestingly, in the engine I took apart these holes were not plugged:

 

This tells me that the cavity was unpressurized. Also, there was no leaking behind the points. This engine was the older version with the non-adjustable balance weight chain, probably `73, but there`s the engine number for reference. All the bearings were in perfect condition, so it was functional like this. So my question is, how many versions of the oil passage routing existed and which is the best to follow when considering an engine rebuild? Perhaps this engine had some upgraded routing with old style non-adjustable chain? 

Another thing: if I`d like to upgrade my `73 engine with adjustable balancer weight, what parts do I have to buy? The adjustable shaft only or the weight as well?

Thanks for sharing any ideas,
Greg.

[tr1ppler]

I'm interested in the oil passage modification as well since I just picked up an unmodified 73.

[jayteenz]

Scrambler - I don't know much about the oil passage issues but if you go to the old Toby Folwick TX750 site, on the right hand side of the home page you will see a listing for "Service and Parts Bulletins". In that section under "Adjustable balancer shaft installation instructions" is a complete guide on the parts required and how to install the new balancer system.
JT

[scrambler]

Thanks Jayteens, seems super helpful! It appears that the the weight #2 is to be replaced together with the shaft, that makes things a bit harder..

[farmrjohn]

Scrambler-It looks like most of the necessary components are available either on ebay or from Speed and Sports store.speedandsportinc.com/

[scrambler]

Thanks, it looks a little pricey, I think I`m gonna start looking for a wreck engine from `74.

[farmrjohn]

Sept 14, 2016 13:58:18 GMT -5 scrambler said:

Thanks, it looks a little pricey, I think I`m gonna start looking for a wreck engine from `74.

One of the warranty replacement engines from a '73 without a serial number might have the modifications as well depending on when it was installed.