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jonbill

Valve spring seat pressure

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Hi, 

I've been running a. 585 lift 307/8 duration cam for 3 years now (8 or 9k miles). 

A couple of the lobes have just started to lose material from near the tips. And I'm looking for how to avoid when I fit a replacement copy of the cam. 

 

The cam is reground from an oiled 1981 f54 l28. 

I have Schneider 68025 springs with a seat pressure = 125 lb ( I think)

 

Are the seat pressures too much? I could swap for 68022 springs at 110lb.

 

Should I use a spray bar too? 

 

Was I just unlucky or used the wrong zddp additive this year? 

 

Thanks for any pointers. 

 

Jon

 

 

 

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Posted (edited)

I can't answer your question about spring seat pressure but you didn't say anything about what rocker you're using.  Do not use re-ground/surfaced rockers. Use only new Nissan OEM rockers. I would use both a drilled cam and spray bar with a high volume pump. Lucas makes a good ZDDP additive or just go with a good racing oil like Brad Penn with zinc already blended in.

Edited by rossman

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7 hours ago, rossman said:

I can't answer your question about spring seat pressure but you didn't say anything about what rocker you're using.  Do not use re-ground/surfaced rockers. Use only new Nissan OEM rockers. I would use both a drilled cam and spray bar with a high volume pump. Lucas makes a good ZDDP additive or just go with a good racing oil like Brad Penn with zinc already blended in.

Thanks, yes, they were new Nissan ones. They don't have any damage. It has a high volume pump.

Thanks for info on spray bar and lucas zddp.

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23 minutes ago, JMortensen said:

It's been 20 years so my info may be out of date, but my machinist who did my E31 picked Schneider springs because they had much lower seat pressures than the competition, which I think was Erson and ISKY. 

Thanks, they've certainly worked fine for 3 years with lots of revs, so no real reason to suspect them other than search not showing anyone here using the 68025 springs. 

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Do the couple of lobes that have lost material look like they've been overheated? if they do are the oil ways partially blocked or could the original hardening depth be thin where the cam was re-profiled?

 

 

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9 hours ago, zbloke said:

Do the couple of lobes that have lost material look like they've been overheated? if they do are the oil ways partially blocked or could the original hardening depth be thin where the cam was re-profiled?

 

 

Thanks. DSC_0270.thumb.JPG.a0a3872f3edcc98b160d3c5bd4c955ca.JPGThere's no discolouration, just missing material, so assume not overheated. Oil holes are definitely clear.  Could be thin hardened depth, I'm ignorant of any treatment applied to cams TBH. 

 

 

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I use a Schneider cam in my 240Z and I heard that they suffer from soft core issues. Because of this, I had my cam nitrided before installing it, and I also use high zinc motor oils, mainly rotella-T. I've got about 5k on my build and currently no signs of cam wear

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Thanks. 

My engine I suppose got to about 6 or 7k miles before I discovered this wear. I've always used zddp additive with decent synthetic oil. I've had the cam repaired and discussed the springs with the cam grinder/repairer and others and consensus is that the schneider 68025 springs are a little too stiff for the L engine rocker arm setup; I probably have near 300 lb pressure at full lift with them. So I've bought some 68022 which are in the right range. 

I'll also be stripping the engine down and drill the block oil jet out to 3mm over the winter. 

I'm hoping those two changes should see it good for many more miles. 

 

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You shouldn't need to drill the oil restrictor out at all. Plenty of oil available by Spray Bar system or internal oiling of Camshaft. 

 

One caveat, idle speed. With higher pressure springs or ven stock springs with a more aggressive profile, increase idle speed to no less than 1,000 RPM. Local Datsun Engine guru Andy Pearson ( Specialty  Engineering ) recommends this on all of his modified engine builds. Since Andy's car have hold 5 SCCA GT3 runoff titles in 5 invites ( An SCCA record ) ... pretty sure he knows what he talking about.

 

BTW,  he's done a lot of oil testing with Big Camshafts. Motul 300V has proven the best oil to use on REALLY big Camshafts. Some of his " Street " stroker engines have over 0.600" valve  lift.

 

Rockers will sometimes fail before cams with OEM Japanese cam cores . This is a result of either oil film failure or Valve floating. You will see a pitting or flaking of rocker pad. This is a metal fatigue failure. Either oil film breaks down, or you have Valve float. Usually valve float. You get a hammering effect on Cam Lobe and Rocker arm when Valve bounces on seat. Pound the s**t out of the Valvetarin. 

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Thanks,  that's really interesting about the idle speed. Since I installed this engine it's been idling at 1100, except this spring I installed Speeduino mapped ignition and dropped the idle to 950, just because I could really. I did maybe 2k miles like that before I found the damage. 

It would be very nice to not strip and rebuild the bottom end this winter to drill that oil jet.

Maybe I'll just fit the new springs, skim the head up to 12:1 and finish the conversion to EFI. 

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