One other factor is that OHC motors usually have relatively low valve spring pressure.
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| Earl.... https://www.slantsix.org/forum/viewtopic.php?t=21351 |
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| Author: | emsvitil [ Sat Jan 06, 2007 11:01 pm ] |
| Post subject: | Earl.... |
I've been thinking (i was trying to go to sleep.....) about the lack of zinc,etc in the newer oils due to the use of roller tappets instead of flat tappets in the newer engines. Thus the recommendation to use diesel rated oils......... But thought of this: With SOHC & DOHC engines there isn't a roller tappet but a cam follower or rocker arm without a roller contacting the cam lobe. The follower is sliding contact (similiar to a flat tappet).... So how do the newer engines avoid wear problems on the cam followers with the newer oil????????? |
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| Author: | mpgmike [ Sun Jan 07, 2007 10:21 am ] |
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The fact is the newer oils are only detrimental during initial break-in. Use racing oil or diesel oil for the first 2 oil changes (at least 5k miles), then you can go to the new conventional oils and be fine. Newer vehicles since about 1990 have used roller cam set-ups which would not be affected, and they get an initial break-in at the factory. Mike |
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| Author: | AnotherSix [ Sun Jan 07, 2007 10:38 am ] |
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A second factor with overhead cams: They do not have a tapered face on the cam lobes and convex lifters, so they have a much great area in contact with the follower. They also sit in a puddle of oil. I have used a small amount of GM eos in two of my cars for a few years now at every oil change with no problems as far as deposits. Quite a few people I now do this. |
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| Author: | slantzilla [ Sun Jan 07, 2007 3:23 pm ] |
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One other factor is that OHC motors usually have relatively low valve spring pressure.
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| Author: | dakight [ Sun Jan 07, 2007 5:13 pm ] |
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Roller cam followers do exist though I don't believe they are widely used at present. |
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| Author: | 440_Magnum [ Sun Jan 07, 2007 5:43 pm ] |
| Post subject: | Re: Earl.... |
Quote: I've been thinking (i was trying to go to sleep.....) about the lack of zinc,etc in the newer oils due to the use of roller tappets instead of flat tappets in the newer engines. Thus the recommendation to use diesel rated oils.........
That last statement just isn't true. Almost all OHC engines today have roller cam followers. The days of cams pushing directly on followers sitting on the valve stems is long gone, they all have "finger' followers or rockers today with rollers and hydraulic automatic lash adjusters. I certainly know my 1993 Chrysler 3.5 does. The Caddy Northstars do. The Phord modulars do. Can't think of one that DOESN'T in fact, but I'm not familiar with the imports.But thought of this: With SOHC & DOHC engines there isn't a roller tappet but a cam follower or rocker arm without a roller contacting the cam lobe. But on the whole, I think the whole lack of zinc thing has been overblown. For one thing the cams that Hughes, etc. are so worried about are radical grinds that use a lot more spring pressure. For another, the very synthetic oils they are grousing about are better lubricants than mineral oil, so they NEED less zinc. And finally, to be safe just use the Mobil 1 "extended life" oils- they are deliberately a couple of API service ratings behind the most recent one BECAUSE they have more additives than the current rating allows. |
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| Author: | dakight [ Sun Jan 07, 2007 6:01 pm ] |
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Well, ya learn a new thing or two every day! I did some looking and sure enough roller cam followers are the norm these days having replaced the previous sliders in most applications. |
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| Author: | emsvitil [ Sun Jan 07, 2007 6:14 pm ] |
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The overhead cam engines I've seen haven't had roller followers(I'd love to do a retrofit on my toyota).......... Some have been hydraulic, some shim adjustment, some screw adjustment.......... The lighter pressures make sense though. So I'll revise the statement and say that some SOHC and DOHC engines have roller followers and some don't........... 
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| Author: | dakight [ Sun Jan 07, 2007 7:06 pm ] |
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Here's an excerpt from the allpar.com writeup on the 4.7L V8: Quote: A head mounted camshaft on each cylinder head operates the valves through a set of needle bearing roller rocker arms, with opposite-end hydraulic lash adjusters acting as the fulcrum, a system not unfamiliar to anyone who's ever played with an 1988 or newer Trenton I-4 (2.2 or 2.5L). But looky here, the Intake and Exhaust rockers are opposite each other. Yup, it's almost a Hemi.
The 3.7L V6 is identical except that it is shy 2 cylinders and the associated hardware.
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| Author: | emsvitil [ Sun Jan 07, 2007 8:05 pm ] |
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Quote: Here's an excerpt from the allpar.com writeup on the 4.7L V8:
that usually means needle bearings on the shaft, and a roller tip on the valve, but it doesn't say if there's a roller on the cam.............
Quote: A head mounted camshaft on each cylinder head operates the valves through a set of needle bearing roller rocker arms, with opposite-end hydraulic lash adjusters acting as the fulcrum, a system not unfamiliar to anyone who's ever played with an 1988 or newer Trenton I-4 (2.2 or 2.5L). But looky here, the Intake and Exhaust rockers are opposite each other. Yup, it's almost a Hemi.
The 3.7L V6 is identical except that it is shy 2 cylinders and the associated hardware. |
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| Author: | dakight [ Mon Jan 08, 2007 4:08 am ] |
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True enough... I guess I could pull the valve cover on Wifee's Liberty, but probably not. |
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| Author: | emsvitil [ Mon Jan 08, 2007 4:54 am ] |
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Quote: True enough... I guess I could pull the valve cover on Wifee's Liberty, but probably not.
You don't have the factory manual to look at the diagrams............ (I won't tell Dan if you don't )
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| Author: | dakight [ Mon Jan 08, 2007 10:18 am ] |
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It's still under warranty so we take it to the stealer for everything right now. When it hits 36K I'll start doing the routine stuff myself. Actually, the stealer will do my oil/filter changes free as long as I own the car but that means a minimum 2 hour chunk of my time on a Saturday morning so I'll probably not continue that beyond the expiration of the initial warranty. On top of that I have to watch them like a hawk so they don't sell me something I don't need. The car was about a year old when I caught them red-handed. They told me I needed wiper blades but I had put new ones on it the night before. I'm very cagey with them now. They haven't tried to sell me anything else - probably afraid to after the email I sent to the Service Manager. |
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| Author: | 440_Magnum [ Mon Jan 08, 2007 11:42 am ] |
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Quote:
that usually means needle bearings on the shaft, and a roller tip on the valve, but it doesn't say if there's a roller on the cam.............
There is. Just about all modern engines have roller followers of one type or another.
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