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Rocker slipping


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#41 Scottz

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Posted 01 January 2011 - 11:22 PM

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.


#42 PZG302

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Posted 02 January 2011 - 06:00 PM

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.



#43 Lurch ™

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Posted 02 January 2011 - 06:47 PM

Good on you for helping him out PZG ;)
This thread was becoming 'cringe-worthy'...

#44 Scoota G

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Posted 02 January 2011 - 06:50 PM

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.

#45 PZG302

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Posted 02 January 2011 - 07:39 PM

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.

#46 bullzed

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Posted 02 January 2011 - 08:31 PM

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?

#47 Gareth. J.

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Posted 02 January 2011 - 08:37 PM

You should check the timing after the adjustments you have made, I'm tiping thats out too which will make it run like crap  ;)

#48 PZG302

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Posted 02 January 2011 - 10:26 PM

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.


#49 bullzed

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Posted 03 January 2011 - 12:48 PM

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?

#50 PZG302

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Posted 03 January 2011 - 01:30 PM

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....

#51 bullzed

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Posted 03 January 2011 - 02:50 PM

Matt,

It's spitting the number 5 and number 6 inlet valve lash pads. We had it running up at 5.5k and it was fine, we turned it off, went to take it out on a run and bam, starting it up fired the lash-pad off number 6.

These are the 2 rockers that started playing up when it had the bad setup (jumping off and whatnot). Could it be that these 2 springs were weakened quicker than they normally would have been?

Also, is it possible to get the springs off without removing the cam shaft or is that not an option?

#52 bullzed

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Posted 03 January 2011 - 03:00 PM

We've also noticed that there is a large amount for the lash pad to move sideways in the valve spring caps. This could be wear from the dodgy set up plus the rockers?

#53 PZG302

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Posted 03 January 2011 - 03:08 PM

zac,

Come round and pick up the other bits from me, sounds like the retainers, for want of a better description could also be worn, the lash pads should sit in the cap but shouldn't really have a lot of sideways movement, if there is more movement in 5 and 6 inlets compared to the other inlets then it would be fair to say that is the case.

Matt


#54 bullzed

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Posted 03 January 2011 - 05:54 PM

So, after different lash pads, different rockers, different valve springs and different spring retainers, it still jumps off.

Also, look what we found in cylinder 6.
Posted Image

As we pulled the nylon cord out, that snagged on it and came out of the cylinder. Possible valve and valve seat damage I guess.

#55 xa1973

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Posted 03 January 2011 - 06:05 PM

:o

Id be pulling that whole head assembly off the block............

#56 peter mc

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Posted 03 January 2011 - 06:08 PM

you may have a bent or sticking valves i think it time to take the head of and have it repaired by a pro.

#57 bullzed

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Posted 03 January 2011 - 06:15 PM

That's the next step. See the damage that little bastard caused. This is horrible.

#58 Lurch ™

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Posted 03 January 2011 - 06:48 PM

ZAC, a + karma for staying with it mate :)
  I keep getting a  -karma ....... :'(        so seems someone doesnt like me helping.....................W  T  F!!
so , that " metal" thingy?........... if thats IN the cylinder.... time to take off the head? :-[  not sure what that is?
you dont have a gremlin there.......... do U?....LOL
I have 3 head jobs about to get under way...........NO!!!! not that type of head job!!!
as I have blueprinted a n E 31 head ...... about .....hhhhhhmmmmmm...............................1974 :P
I may give a blo by blo account of the 3 heads as I go.
the heads are a P90, and 2 E88's... one has 260 valves... the other 280 valves... I also have a crow cam , but I tend to like a different cam grinder who gave me a grind,  180 RWHP @5000, L260 block,E31 head job..... back in 70's
damn Ive highjacked the thread :-[ :-X :'(
sorry Zac ............. :-[ :-[ :-[ :-[ :-[


You are fair dinkum out of your tree, Salty... ::)
That diatribe above has nothing to do with the topic! Go away & only return when you can post a sensible & ledgeable comment!!! >:(

#59 PZG302

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Posted 03 January 2011 - 07:39 PM

Zac,

Sorry to see you have found the problem, and it wasn't what you were hoping :'(

Never good to see things sitting in cylinders.

As Peter said it's time to pull the head off and see what's what in there. Hopefully no damage to piston or bore. If it's a simple fix of new valve, make use of the bits you have there where you can to save a few dollars.

If the bores are good, and block looks suitable to use for a 3mm overbore I'm sure we can work something out on a swap with my spare N42/N42 motor if you need to go down that path.

Stick with it, it will be worth it in the end..... :o


#60 bullzed

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Posted 03 January 2011 - 09:11 PM

LOL, salty, you're a funny one  ::) thanks mate

I'll be pulling the head off tomorrow and yeah hopefully no damage to the piston or bore. Thanks again for all the spare bits you've supplied me with, you've undoubtedly saved me money AND time.  ;D

You've helped me so much, we'll have to work something out, you're just too generous!  :P

I'll keep you updated with the condition of the bore and head tomorrow.




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