Centistoke oil rating

[rebelrouser]

I just installed a set of Morell hydraulic roller lifters in a BBC engine, in reading the instructions they recommend a Centistroke rating of less than 15cSt at 100 degrees C. I looked and found out what Centistroke means, and it is related to viscosity. I looked up a couple oils I use and no Centistroke ratings. I found a general Machinery Lubrication chart and it lists 40 weight oil as having a rating of 12.5 to 16.3 Centistokes. and 30 weight 9.3 to 12.5 Centistrokes. Any comments and info on this rating are welcome.

[HDBD]

There are many good oils that fall into this category and offer multi viscosity protection such as 15/w40 for example. Probably most relevant for street cars that are subjected to cold weather.

[ottocycle340]

I'm an oil guy, and not a hardware guy, but my assumption is that the manufacturer has a concern with the engine oil being too viscous for proper operation of the hydraulic lifter. With too viscous an oil, proper flow through the lifter may be compromised because of the size of clearances and oil passages.

You should be good with any high-quality multi-viscosity 30 or 40 weight engine oil (5W-30, 10W-30, 5W-40, 10W-40, 15W-40, etc). Keep in mind that the first number with the 'W' is the Winter Grade and it represents only the oil flow at very cold temperatures. The smaller the Winter Grade number, the better the oil flows at cold temperature. The last number (20, 30, 40, 50, etc.) is what is relevant to recommendation of 15cSt @100C because the last number of the viscosity grade is determined by the viscosity measurement at 100C.

If you want to see how automotive oil viscosity grades are determined, do a search for SAE J300. The search result will be a chart defining the temperature and viscosity measurements of each SAE viscosity grade.

[RDY4WAR]

A 15 cSt is the middle of a 40 grade per SAE J300 which is measured at 212°F (100°C). This is referred to as the KV100 or kinematic viscosity @ 100°C.

xW-20 = 6.9 - 9.2 cSt
xW-30 = 9.3 - 12.4 cSt
xW-40 = 12.5 - 16.2 cSt
xW-50 = 16.3 - 21.9 cSt

The real issue is at lower temperature around 100°F where a 15 cSt KV100 oil will be upwards of 100 cSt. I tend to recommend sticking with a 30 grade or lower with Morel lifters.

This is where engine blueprinting comes to play. For example, if you build the engine with wide .003"+ bearing clearances, that require a 50 grade oil, then you don't want to use Morel lifters or thin and low tension rings requiring a 30 grade. Note that the bearings always take priority when it comes to viscosity needs.

[novafornow]

RDY4WAR - I always look forward to your posts, but I have a little M with 0.003" mains and run Mobil 1 0-30 and love it. Great oil pressure and mains looked great last look. 50 wt for 0.003" is a little overkill to me, but I totally get where you were going with that statement.

[MELWAY]

RDY4WAR - I always look forward to your posts, but I have a little M with 0.003" mains and run Mobil 1 0-30 and love it. Great oil pressure and mains looked great last look. 50 wt for 0.003" is a little overkill to me, but I totally get where you were going with that statement.

What kind of application and engine temps do you operate in?
I’m slowly getting out of that 50wt thinking myself

[Elroy]

Why does a Morel lifter require specific oil types while an OE lifter and others do not? What is different?

[rebelrouser]

I actually think the newer OEM engines all require a thinner oil, and at least a synthetic blend, I just don't think they spell out the lifters by themselves needing a thinner oil. I have seen some posts and my own experience with a couple of newer vortecs that with thicker oil they do not lube the pushrods as well, and are finicky to get adjusted.

[RDY4WAR]

RDY4WAR - I always look forward to your posts, but I have a little M with 0.003" mains and run Mobil 1 0-30 and love it. Great oil pressure and mains looked great last look. 50 wt for 0.003" is a little overkill to me, but I totally get where you were going with that statement.

I agree completely. A clearance of .0028-.0030" could be happy with a 30 grade depending on which 30 grade and the use of the engine.

Conservatively safe targets, at 212°F operating oil temp, are below. This is what I go by as a starting point. It can sway quite a ways from this for some applications, especially in racing.

.0016-.0021" = 20 grade
.0022-.0027" = 30 grade
.0028-.0033" = 40 grade
.0034-.0039" = 50 grade

[Elroy]

I actually think the newer OEM engines all require a thinner oil, and at least a synthetic blend, I just don't think they spell out the lifters by themselves needing a thinner oil. I have seen some posts and my own experience with a couple of newer vortecs that with thicker oil they do not lube the pushrods as well, and are finicky to get adjusted.

I am sure there may be something to that. But, I have actually straightened out some higher rpm stability issues using GM lifters by going to thicker oil, going from 20 or 30w to 40 or 50w...all ran quiet. And regularly use 40w with GM lifters, as does GM currently. 0w40 is called out on several GM applications currently, and 50w Mobil recommended in some severe applications.

I know there are a lot of moving pieces here, but was just curious why one manufactures lifters would be finnicky to oil weight. There has to be some flexibility there, an oil goes through many stages of viscosity as it heats up, is cold, ambient temp, etc etc.

[David Redszus]

The actual viscosity of an engine oil is a function of its operating temperature at the point of lubrication.
It is very possible that several oils, having identical viscosities at 100c, would have different viscosities at
higher (or lower) temperatures.
.............100c........150c
10w30......15.0........6.8cSt
10w40......15.0........5.9
15w40......15.0........5.6

[novafornow]

RDY4WAR - I always look forward to your posts, but I have a little M with 0.003" mains and run Mobil 1 0-30 and love it. Great oil pressure and mains looked great last look. 50 wt for 0.003" is a little overkill to me, but I totally get where you were going with that statement.

What kind of application and engine temps do you operate in?
I’m slowly getting out of that 50wt thinking myself

Drag bracket, low 10s, 2900lbs, 7500 max RPM. Runs 200 and above when hot lapping.

[Roundybout]

How does one decide oil viscosity on a roller bearing equipped crankshaft such as a small 4-stroke scooter/motorcycle engine?

I’ve been helping my son with his forced air cooled 150cc-180cc scooter engines he and his friends fool around with. Cylinder head temps in the 300F-340F range with oil temps in the 240F-275F range. Been using Mobil 1 0W/40 European formula and it seems to be ok. Some scuffing on piston skirts here and there. Have to be run a bit rich to keep them alive and giving up some power. Especially in this 95F-100F weather we’ve been having. Was thinking at those temps something in a 50W would be better?
Mobil 1 0W/50?

[RDY4WAR]

How does one decide oil viscosity on a roller bearing equipped crankshaft such as a small 4-stroke scooter/motorcycle engine?

I’ve been helping my son with his forced air cooled 150cc-180cc scooter engines he and his friends fool around with. Cylinder head temps in the 300F-340F range with oil temps in the 240F-275F range. Been using Mobil 1 0W/40 European formula and it seems to be ok. Some scuffing on piston skirts here and there. Have to be run a bit rich to keep them alive and giving up some power. Especially in this 95F-100F weather we’ve been having. Was thinking at those temps something in a 50W would be better?
Mobil 1 0W/50?

The design and contact points of a roller bearing don't really allow for an oil wedge to induce full hydrodynamic lubrication. It acts much the same as a roller lifter on a cam lobe in mixed and boundary lubrication much of the time, regardless of the oil's viscosity. These engines are usually splash lubricated which will have an impact on viscosity. Both too low and too high of viscosity have issues with splashing. Too high of viscosity, think of trying to splash syrup. Too low of viscosity can get flung away from the splash arm due to windage parting the oil around the arm like the red sea. The range I like is 5-100 cSt. That's broad but think a 10W-30 is ~10 cSt @ 212°F and ~70 cSt @ 100°F. That gives you that range of operation. A 0W-50, 5W-50, or 15W-50 will be >150 cSt @ 100°F which can cause some splashing issues at low temperature. A 0W-40 or 5W-40 will be upwards of 100+ at that temp as well. This could be where your scuffing on the piston skirts is coming from if you aren't getting sufficient oil splash due to it being too viscous, gradually improving with temperature.

In the kart racing world, a lot of people use 0W-20 or 5W-20. Teardowns look perfect with no scuffing or accelerated wear anywhere, and this is in engine highly modified 4-stroke 1 cylinder splash lubricated engines turning 7000+ rpm. Even with a journal bearing, the IMEP/BMEP isn't high enough to exceed the film thickness of a 20 grade.

[Roundybout]

How does one decide oil viscosity on a roller bearing equipped crankshaft such as a small 4-stroke scooter/motorcycle engine?

I’ve been helping my son with his forced air cooled 150cc-180cc scooter engines he and his friends fool around with. Cylinder head temps in the 300F-340F range with oil temps in the 240F-275F range. Been using Mobil 1 0W/40 European formula and it seems to be ok. Some scuffing on piston skirts here and there. Have to be run a bit rich to keep them alive and giving up some power. Especially in this 95F-100F weather we’ve been having. Was thinking at those temps something in a 50W would be better?
Mobil 1 0W/50?

The design and contact points of a roller bearing don't really allow for an oil wedge to induce full hydrodynamic lubrication. It acts much the same as a roller lifter on a cam lobe in mixed and boundary lubrication much of the time, regardless of the oil's viscosity. These engines are usually splash lubricated which will have an impact on viscosity. Both too low and too high of viscosity have issues with splashing. Too high of viscosity, think of trying to splash syrup. Too low of viscosity can get flung away from the splash arm due to windage parting the oil around the arm like the red sea. The range I like is 5-100 cSt. That's broad but think a 10W-30 is ~10 cSt @ 212°F and ~70 cSt @ 100°F. That gives you that range of operation. A 0W-50, 5W-50, or 15W-50 will be >150 cSt @ 100°F which can cause some splashing issues at low temperature. A 0W-40 or 5W-40 will be upwards of 100+ at that temp as well. This could be where your scuffing on the piston skirts is coming from if you aren't getting sufficient oil splash due to it being too viscous, gradually improving with temperature.

In the kart racing world, a lot of people use 0W-20 or 5W-20. Teardowns look perfect with no scuffing or accelerated wear anywhere, and this is in engine highly modified 4-stroke 1 cylinder splash lubricated engines turning 7000+ rpm. Even with a journal bearing, the IMEP/BMEP isn't high enough to exceed the film thickness of a 20 grade.

Excellent info. These engines are splash lubricated but also have an oil pump that sends oil to the valve train. While back we did try some 50 weight (Mobil 1 I believe) and honestly that showed the most piston skirt wear along with a slight but measurable rise in the average temp under a sustained load. These are warmed up gently and not hammered on until up to temp. At least 160F oil temp. Used to run Rotella but that showed the worst wear. A quality synthetic seems to be so much better. There’s such a temp difference from being cold to hot being air cooled that I’m not sure if opening up the piston to wall clearance would be a benefit. Too much and they seem to have excessive blow by until really hot and up to temp. Too little? We have all ready found out the limit there lol. Thanks for the info again.