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bullzed

Rocker slipping

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Hey RB30X,

              Your quote (The lash pads "should" be directly under the cam lobes) 

As Gary Coleman would say:

                    "What chew talkin bout"

The Lash pads are on top of the valves. Directly under the cam lobes is the rocker wipe pad.

 

Bullzed.

        Valve clearences should be checked between the back of the cam lobe and the rocker wipe pad. That is with the lobe facing away from the rocker.

Also since you have a oiler cam, check with a thin piece of wire that the oil holes are not blocked on the lobes that have worn rockers. And as Salty has suggested check all the rockers for a wipe pattern that does not extend off the ends of the hardended wear area. The lash pads look to be reasonably tall so I presume this is an aftermarket camshaft. With standard valve spring retainers the maximum thickness of the lash pad should not exceed 170 thou.

Regards

David.

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Thanks for clearing that up guys. I've checked the oil holes (when we had it running without the rocker cover on), they're all working perfectly. The wipe patterns are really deep and some of the rockers are chipped. It's apparent that there's something wrong there as others said they'd never seen the 'deep' wipe patterns before. This is an aftermarket cam however all the work was done by the owner of the motor before me. The cam is an E30, i'm not up to date with all that so I would have no idea what lash pads are needed. What measurement shouldn't exceed 170thou?

 

I measured from the bottom to where the rocker sits in the lash pad and it's 6.76mm (0.266 inches [is this the measurement that shouldn't be exceeded?]). Another thing worth noting is that the lash pads spin freely, is this normal? The rockers are bouncing out so much that it's giving the lash pads time to spin.

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Where in Brisbane are you? I'm not sire of my movements over the next few days, but I should be able to take a quick look at what's going on with these rockers. What you're describing should not be possible with everything working as it should. Sounds like whoever set up the head got something very wrong.

Matt

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I'm over in Chapel Hill. Your help would be massively appreciated. I can tell there's something incredibly wrong with the state of the rockers and the fact that the rockers are jumping out of the lash pads!!

 

I'm home the 1st and 2nd of Jan but work 9am - 1pm on the 3rd. I'm only 17, so, don't be surprised hahah.

 

The name's Zac.

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No worries Zac, pm me your contact details and I'll try to get over on the 2nd. Tomorrow looks like it will be a lazy day to recover from tonight  ;D

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  when i set up motors with ground cams i sometimes end up with 6 to 8 different size lash pads, that my friend is a good job, there are so many variations wouldnt it be nice if they were all the same , lash pads come in 10 thou increments , this is the idea ,adjustment, if there all the same obviously not much adjustment has been carried out , i have a kit that has 14 different size lash pads to juggle and set up cams with,, mind you checking each valve requires a somewhat patient attitude

 

Ditto... ;)

 

Im more concerned about this " new cam grind " and the valve train as a whole, sounds like someone bit off more than they could chew and only did half the job required to match the new cam specs, driveway warranty at its best...Im also curious to read the verdict

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Dazzed and Salty you are both correct in what you are saying the valves do have to be exactly the same height to start with but the lash pads need to be individually fitted as there is no predetermined thickness lash pad to use with a reground cam because many variables effect the thickness needed.

The only sure way to determine the correct lash pad thickness is to check the cam lobe wipe pattern on the rocker arm rubbing pad.

Therefore it must centered other wise the wipe pattern will go off one end of the rubbing pad resulting in the destruction of the cam lobe and rocker arm. 

There is all so other checks that help, i like to be sure that i have the same lift with a dial indicator if you have diffrent lift numbers you have not done it right. As your rocker arm ratio will not be right, the max variation between valves should not vary by more than 0.005 inch

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yer it nice when the valves are the same height it makes the job a hole lot nicer. its when you put a cam in a engine that has been around and you have to have 12 diffrent shims that when you earn the big bucks....hahhah

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so far you keep spitting out rockers , now your running out to get another set to spit out  and , why dont you get a specialist to set it up properly so you can gain the maximum benefit from the cam and tune it up , another set of rockers will not help you.

 

No offence but I find your tone a little condescending. In no way do I intend to just swap my rockers out and think it's solved the problem, I'm not that ignorant. I intend to let Matt have a look at the head to determine what really needs to be done.

 

I don't want this thread to turn into an argument about personal setups, I will update everyone as I learn more about the head setup from Matt.

 

I appreciate most of your guys patience with me and my lack of knowledge but I would prefer to be treated with more respect by others.

 

Cheers

 

Zac

 

 

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yer it hard to give addvice and try to explane things to people that have not got the experience and time under the bonnet i find it very hard to give a simple explanation to a very complex problem  with out sounding like a prick...

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Don't give up Zac, you're on the right track. You only fail when you stop trying, so don't stop.

Practice, practice, practice, makes perfect.

Unfortunately, sometimes the long way 'round is the shortest way there (sounds weird but can be so true)!

 

Books for after dinner reading :

How to rebuild your Nissan/Datsun OHC engine.

Nissan Part No. 99996-M8013

Tom Monroe

Published by HP Books, Inc.

ISBN 0-89586-095-3

 

How to modify your Nissan/Datsun OHC engine.

Nissan Part No. 99996-M8012

Frank Honsowetz

HP Books, Inc.

ISBN 0-89586-353-7

 

'Trusty' Haynes Manual:-

Datsun 240Z, 260Z, 280Z......Automotive Repair Manual.

28012 (206)

by J H Haynes and P G Strasman.

Haynes Publishing Group.

ISBN 0-85696-206-6

 

If your in Brisy, drop into Ivan Tighe Engineering and get the best advice from one of Australia's best head and cam specialists. Or email/call them for a few tips. (Ask for Dean Tighe, for technical help).

http://www.tighecams.com.au/

 

Are you getting any "Valve Bounce"?; this occurs when the engine is revved higher than the valve springs will permit. The valve will no longer follow the cam profile and will crash back onto the valve seat. This will cause loss of power and , if prolonged, will cause valve failure, shorten camshaft life and cause considerable damage to engine components.........

It does not need a lot of revs to get valve bounce with badly fatigued springs.

If springs are really fatigued you can get some funny tell tale signs on the rockers 'cause the cam is slamming into the rocker instead of riding on it with constant spring pressure. The sudden jarring effect can knock things out of whack.

 

Best of luck mate and enjoy the reading.

 

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Looks like we have the problem solved.

 

Hopefully Zac will be working away feverishly polishing rockers to replace the current set.

 

It turns out that who ever refurbished the motor previously thought you needed lash pads about 1/2 inch thick, which meant the posts for the rockers to pivot on had to be wound all the way down throwing the geometry way off. This meant the rockers were only just on the edge of the pad and that allowed the lash pad to spin. The geometry was so far out that the ends of the rockers were ovoid where they sit on the pivot and were rocking side to side just to operate, again exaserbating the problems with the rockers being spat sideways.

 

Another, more sensible, lash pad was tried and the pivot post had to be bought up about 10mm or so to get the required cold clearance. The wipe was tested and whilst not perfect was a lot better than the previous set up.

 

Zac picked up a set of rockers and lash pads I had from a spare head. These should keep him on the road until he is ready for a proper rebuild. All going well he should be back on the road tonight or tomorrow.

 

So as is usually the case, keep it simple stupid to look at the basics first.

 

 

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Good on you for helping him out PZG ;)

This thread was becoming 'cringe-worthy'...

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Hell yea i was ready to fly up and help him myself, would've got really sore arms but.

 

Any more description on the lash pads? They sooooo look just like a set i sold on ebay a few months ago.

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About 1/2 inch or so thick and also didn't have the little channels on each side like the standard ones have. Also very obviuosly machined up aa "aftermarket".

 

The motor apparently was out of a patrol, so I'd say old mate who refurbished it wasn't used to the L series motor. I'd say when he was told that a bit was taken off the cam for the regrind he got some lash pads made up with the extra meet in them to make up for what was taken off the cam.

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Thanks heaps to Matt who helped me out today. The first half of the problem was definitely the massive lash-pads and the fact that the rockers had near no adjustment.

 

I've fitted the rockers and more sensible lash-pads, checked clearances and then started it up. While it now doesn't spit rockers any more, the engine still insists on coughing and backfiring and carrying on every now and then. There's a metallic sound as well when it coughs and carries on which makes us think it's probably a valve spring problem. Anyone have any ideas about this problem?

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Zac, not the recommended thing to do, but after checking timing and mixtures, if you still believe it is valve springs you can try the spares I have.

 

I would say that getting the rocker geometry back to where it should be has put the cam timing out a bit. Have read of the cam section in the books I lent you, that should point you in the right direction. Get the cam timing to where It should be then the rest should fall in place.

 

The cam gear on the front is adjustable for setting the timing. Because the rockers were set up way out originally, now they are better set the cam will now be out compared to how It was before and this will need to be set up again to get everything back in sync. The adjustment should only be couple of degrees.

 

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Dad and I adjusted the timing and clearances twice over this morning and the darn thing is now spitting number 5 intake lash-pad. We tried the spare lash pad and rocker on the port and it's still spitting.

 

As Matt always says, "keep it simple stupid". I think the next thing to check would be the valve springs because the lash pad, clearances, rocker and cam are all fine on that port as well and the timing has been readjusted. Does that seem a reasonable deduction to you guys?

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Zac,

 

If number 5 inlet valve is sitting at the same height as the other inlet valves then you may have an issue with the valve springs.

 

It maybe prudent to replace the valve springs, or get them checked at least. With the set up you had there is no real telling what damage has been done. The valve springs may have been weakened a lot quicker than what would normally happen over time.

 

A new set of valve springs should cost around $150. As I said earlier, if you want to try another set, you can have the spare set I have from the bare head.

 

The only proviso is there is no warranty that they will solve the problem, but they would more than likely get you out of trouble. If you swap number 5 inlet valve springs over and it doesn't spit the rocker and lash pad you may be OK until you're ready for the performance rebuild.

 

if you want to pick them up I'll be home all day today.

 

At least it is only spitting out the one rocker now....

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