Steel verses cast cam followers

[oldchieft]

Hi all
I have been studying various threads and it has raised some questions.

There has been some discussions about modern oils, and the problem of cam and cam follower failures.

I find that there are OE followers, and steel followers.

There is an obvious advantage to the maker to turn a follower from a solid bar then machine cast blanks.

My question is do cast followers work better then steel with modern oils?

What is the state of play with cam blanks?

With piston rings, the match of the hardness of the two surfaces is critical. From memory the hardness has to be close, but must not be exactly the same.

I can't find any information from camshaft makers on this subject.

Has anyone got any up to date information on choice of cam follower for modern oils?

Can anyone with a more recent education in engineering tell me what is the optimum match of surfaces for minimum wear?

Regards

Jon the Chief

[rgh0]

Hi Jon - this is an area of particular interest to me as I have played with a lot of the questions you raise over the years. unfortunately not much published about this topic as most people doing it professionally treat it as commercial secret knowledge and most stuff on the internet about it is wrong. You know the right questions to ask so I suspect your knowledge is not that out of date !!!!

Steel versus - cast Iron followers
Both work OK on cast iron cams. Not sure how easy it is to get cast iron ones these days as all I have used recently have been steel. The steel ones come in varying thickness and can be thinner than the original cast iron ones in top thickness which helps when building high lift cam engines. Be careful of using steel followers on steel cams - see the next topic

Hardness difference
Generally not critical with cast iron on cast iron as cast iron has a very low galling tendency. For chilled cast iron both will be around 70 Rockwell C typically.
Typical steel followers I have tested are around 60 Rockwell C (I presume they are nitrided). Steel has a much greater tendency to gall versus cast iron and a hardness difference with a cast iron cam of 10 Rc is good to prevent galling, thus steel followers work OK with cast iron cams.
Steel followers on steel cams can be a problem as both will be around 60 Rc and you need to get that 10 Rc hardness difference. Typically you want to treat the followers with a DLC treatment ( Diamond Like Coating) to make them harder than the cams some of the suppliers offer this as an option
I have had success with steel followers on cast iron cams built up with stellite spray welding as the stellite approaches 70 Rc hardness

Steel versus Iron Cams
I prefer iron cams for the above metallurgy advantages. Steel cams are stronger but if you use the long cam sprocket bolt modification you don't break cast iron cams. Finding new cast iron cam blanks in the USA appears to have been a problem in the past as I have had cam grinders in the USA ask me about my source for cams in Australia. This does not appear to be problem in the UK.

Running in
Once you have the metallurgy right as above and assuming you have not overload the cam to bucket contact with too heavy spring nose loads and assuming the machining of the cam and followers is right with the right surface finish and profile. Then you should not have problems provided the running in is done OK. Some cam suppliers talk about running in with lower spring loads but I don't believe this is necessary for a twin cam with cam nose loads less than 220 lbs, and nose loads above 220 lbs lead to excessive wear and failure no matter how well it is run in on a twin cam and are not necessary anyhow for even a 9000 rpm engine. Use a good assembly lube to liberally coat the cams and followers (I use Redline). I also phosphate treat the cam and buckets - the phosphate layer also helps bedding in and helps prevents galling during this critical early operation, this is desirable for a race engine with its higher spring loads but probably not really required for a road engine with lower spring loads. I also use a specific engine running in oil (Penrite) that is formulated to assist the initial bed in of cams and followers and rings etc. Follow a good running in procedure ( lots of discussion on this in the archives) and vary the speed and don't idle the engine to long in the first 100 km.

Normal Operation Oil
This is where all the internet debate is about as people say the modern lower ZDDP oils are killing flat follower engines. This may be the case if you get all the preceding stuff wrong and a modern lower ZDDP oil then adds to all your previous mistakes and you have a failure especially for engines with poorer lubricated and heavier valve trains ( eg US V8 and BMC A and B series engines). Get the above stuff right and your twin cam at least will work fine on modern oils. But do use the best quality full synthetic oil. If you are paranoid about ZDDP levels then you can get modern full synthetics with high ZDDP levels if you want but personally I don't believe it is necessary for a properly built road twin cam but it does not hurt.

cheers
Rohan

.

[Esprit2]

Rohan,

Nice write-up... definitely one to save. Thanks for taking the time.

As for the choice of oils. I don't have your depth of knowledge about how to get everything right in the parts (and in some cases still running original parts), and I can't afford to find out in the engine's autopsy that I didn't have it all perfect. Since there's no downside to choosing a high ZDDP oil over a modern reduced ZDDP oil (my cars in question don't have catalytic converters), I prefer to have the cheap insurance policy of more ZDDP. I don't use ZDDP additives, but instead choose a quality oil with higher levels to begin with.

Modern API SN certified oils (I'm in the USA) require that a select few viscosity grades (6 of them?) have only 700ppm ZDDP, while all other grades "may" have up to a limit of 1200ppm. But it's left up to the manufacturer to determine how much to use. A "green" oil company (oxymoron ?) might hold the ZDDP down to 800-1000ppm, while a "performance" company might go for the full 1200ppm. And some companies will vary the ZDDP level by individual viscosity grade within a single product line. You can't tell how much ZDDP is in the oil by simply reading an API SL/ SM/ SN label.

I feel better about covering my vintage engine's needs when I see older API SH/SJ on the label. And then I visit the oil company's website, or call tech service to ask what the ZDDP level is. If they won't say, I won't buy their product. There are helpful oil companies, and I choose to use their products.

Since a modern oil has as little as 700ppm ZDDP, are you suggesting that is an adequate level if the parts choices are right?... considering that we're not automotive companies with the freedom to design in our ideal parts. With what's available to us over the counter from Lotus or Lotus specialists, is 700ppm ZDDP safe? If not, what is?

Thanks,
Tim Engel
(1200ppm personal minimum... currently using 1300ppm or more)

[oldchieft]

Hi Rohan
Good work as always, the cams I have are Piper's and seem to be cast iron or cast steel. Burton list O.E. followers and steel.

The choice of material was brought home to me with marine pistons a liners in days of old you had to change both often, when I finished at sea rings lasted 24,000 hrs and liners never needed changing.

I will look at the things you say over the next few days, I have a remembrance of small item hardening with a powder you put in a tin with the work piece and heated it up, but that was long ago and what the science was I can't recall.

The DLC is something new to me.

The detail about the length of the cam sprocket bolt is worth knowing, I will look that up with a search.

I did think of leaving the inner spring off for running in but did not fancy the rebuild needed to finish the job, and on the whole I reckon if you need to do that you are doing something wrong in the first place.

Piper use phosphate coating on the cam, would coating both surfaces be a big gain?

During the build and pre-start I plan to have a LO priming pump connected, so I hope that will solve the problem of the most critical period of start up.

My take on oils is that old style oil relied on additives too much, and the additives are depleted in service, the case for synthetics I believe is less additives use as the properties are built in at molecular level.

The best way is to engineer the machine for service with any good quality oil, of the correct spec.

Regards and Thanks

Jon.

[rgh0]

Rohan,

......Since a modern oil has as little as 700ppm ZDDP, are you suggesting that is an adequate level if the parts choices are right?... considering that we're not automotive companies with the freedom to design in our ideal parts. With what's available to us over the counter from Lotus or Lotus specialists, is 700ppm ZDDP safe? If not, what is?

Thanks,
Tim Engel
(1200ppm personal minimum... currently using 1300ppm or more)

HI Tim
Certainly for a standard twin cam with original parts I believe the newer oils with 700 ppm ZDDP are perfectly OK, but as you can get higher ZDPP oils you may as well use them, especially if you have modified your engine or dont know what modifications may have been done by others. Like you say its cheap insurance

I believe most of the failures people talk about on the internet in other engines that they ascribe to the oil really relates to engines running modified parts metalurgy ( eg steel versus cast iron) or engines with performance modifications that increase the load on the valve train ( eg. high lift cams and heavy springs) or poor parts manufacture or poor running in practices. The lower ZDDP oil maybe an additonal factor but it is certainly a minor one.

There are many modern flat tappet engines that dont have a problem with cam and follower wear ( eg most Toyotas) so why should older engines be any different if made right.
cheers
Rohan

[rgh0]

Hi Rohan
Good work as always, the cams I have are Piper's and seem to be cast iron or cast steel. Burton list O.E. followers and steel......

.....The detail about the length of the cam sprocket bolt is worth knowing, I will look that up with a search......

......Piper use phosphate coating on the cam, would coating both surfaces be a big gain?........

Regards and Thanks

Jon.

You need to find out exactly what material the cams and followers are. Even the so called OE followers may be made from steel these days as Lotus discontinued using cast iron followers in the 9xx engines many years ago and these were the same part as the twin cam used.

Dave Bean in the US used to supply a drawing for the modification. I would do it certainly to any modified high lift cam I was using, especially critical on the exhaust cam as it carries most of the drive chain load. You bore and tap the cam so the bolt runs past the first bearing. You use a longer bolt with an oil feed passage so the oil from the first bearing can continue to feed down the cam interior to the other bearings.

I would also phosphate treat the followers especially if they are steel and you are running a highlift cam. But if you use the DLC coated followers then you dont use or need the phosphate coating on them

cheers
Rohan

[reb53]

I have a remembrance of small item hardening with a powder you put in a tin with the work piece and heated it up, but that was long ago and what the science was I can't recall.


Jon.

Sounds like "Kasenit" which was a case hardening powder used to introduce carbon into the top layer of steel that contained insufficient carbon for normal hardening.
I think it was taken off the market, or "improved", because of health and safety concerns.

I still have a tin in my workshop and for the sort of things I do it's occasionally useful, but I don't think it has any place in a Twink rebuild.

Ralph.

[oldchieft]

Hi Rohan
The Piper cams are chill cast iron, Burton have not said what the OE followers are made from.

I wonder what you use to to test hardness, I see the are some hand held devices but they cost hundreds of pounds.

Hiring might be an option, if that was available.

Jon

[rgh0]

Rockwell hardness is measured by applying a load with a small diamond tipped tool to the piece and measuring the size of the indentation with a microscope. The Rockwell C scale is based on a specific load and specific sized diamond tool and was established for measuring hardened steels. These days there are a number of automated electronic ways of doing the same thing whose results have been correlated to the original Rockwell scale. Most good machine shops will have a harness tester and will do a test for a smallish fee. I have looked at buying my own hardness tester but at the price its been hard to justify.

cheers
Rohan

[oldchieft]

Hi Rohan
Got some feed back from makers.

Piper don't give hardness numbers, but they state that the cams are chill cast.

I see on-line, numbers for chill casting of 65 to 85 Rockwell C.

Assuming in the middle of that range, and the cams are say 75?

Burton give a number for the followers of: -
"Batch inspection report on our last delivery shows hardness readings between 59 ? 60 Rockwell ?C?"

Kent cams say; -
"Ours are EN40 nitrided with a harness of 58-63 RC"

None of the makers say anything about cast iron followers, so I am assuming everyone goes for the easy and cheap way of turning from steel bar.

So I am likely to end up with a chill cast cam of about 70 to 75 RC, and steel followers of maybe 60 to 65 RC.

If I have read your post correctly a difference of 75 cam and 60 follower would be OK, 70 cam and 65 follower is close to a problem.

I think I will visit my local machine shop guy and ask if he has a tester.

Jon the Chief

[andyhodg]

Hi Jon

I had always thought that the improvements in the running hour in marine engine was due to a better understanding of the cylinder oils used and the modern oils (by modern I'm talking 1980's) countered the acidic products of combustions from the heavy oils. Injecting cylinder oil is some thing that is unique to slow speed diesels.

However your general point is very valid modern engines far out last the engines manufactured in the 60's

All the best

Andy

[rgh0]

Hi Rohan
Got some feed back from makers.

Piper don't give hardness numbers, but they state that the cams are chill cast.

I see on-line, numbers for chill casting of 65 to 85 Rockwell C.

Assuming in the middle of that range, and the cams are say 75?

Burton give a number for the followers of: -
"Batch inspection report on our last delivery shows hardness readings between 59 ? 60 Rockwell ?C?"

Kent cams say; -
"Ours are EN40 nitrided with a harness of 58-63 RC"

None of the makers say anything about cast iron followers, so I am assuming everyone goes for the easy and cheap way of turning from steel bar.

So I am likely to end up with a chill cast cam of about 70 to 75 RC, and steel followers of maybe 60 to 65 RC.

If I have read your post correctly a difference of 75 cam and 60 follower would be OK, 70 cam and 65 follower is close to a problem.

I think I will visit my local machine shop guy and ask if he has a tester.

Jon the Chief

Hi Jon
All those hardness numbers are consistent with what I have measured. I measure the chilled cast iron cams around 70Rc and the nitrided steel followers around 60 Rc. Around 10 Rc unit difference is what you are looking for but a 5 unit difference for steel on cast iron should be OK still.

cheers
Rohan

[oldchieft]

Thanks Rohan
I think this subject has had the best possible treatment and a lot of useful information is now on the record.
Best regards
Jon.

[SJ Lambert]

So, what's the ideal under head length of the cam sprocket bolts when using either chilled or steel cams in high performance applications?

I've noticed that Burton's bolts are about a 1/4" shorter than a pair of OE bolts out of a late model lip seal engine that I've got on hand.

What's the ideal grade of bolt to use?

[rgh0]

Hi James
Give me a couple of days and I will dig out a long bolt and post a photo with dimensions - I have some in a box somewhere just need to find them, as still moving my spare parts storage to my new house. You don't need long bolts for a standard road engine or if using steel cams in a high lift / high rpm application as they are strong enough. If using cast iron cams in a high performance application which is what I prefer from a hardness perspective then you need a longer bolt that reaches past the first camshaft bearing so that the cam is held in compression by the bolt and you also get the bending strength of the bolt itself and thus the assembly is stronger under the bending loads imposed by the chain onto the cam to the first cam bearing.

Surprised your Cosworth engine does not have it already but maybe it was retired from competition work before this mod came into vogue ?

cheers
Rohan