Andrew, Thanks for pointing out - yes I did mean to say always change the valve stem seals. We occasionally went to the considerable trouble of changing the guides on a few heads in the early days - pretty expensive back then too and not really worth it for a street engine and cheaper to toss the head and go downtown to the wreckers and grab another - I guess it really depends on how much has been put into other mods like big valves and porting etc. I'm not sure how it's done these days, back then you had to dunk things in a very hot oil bath, as I said tres exy as it was very labour intensive and no way to do it without the correct gear. Stem seals seem to be made out of a better class of materials these days also, I've seen genuine seals totally stuffed in 70-80K kays, my last set on the old L engine have done 100K kays and still no signs of anything getting down past them, but the guides are absolutely kangaroo teds brother, sorry that's probably a 30yo colloquialism (roo ted).
regards Terry -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of GREENBURY, Andrew Robert Sent: Saturday, 15 February 2003 4:19 PM To: [EMAIL PROTECTED] Subject: RE: L6 Head Removal/Refitting Terry, Excellent informative post. You mention: "change the valve guides (always with an old L head as the guides wear)" Do you mean with every head removal the valve guides should be renewed? Or just the valve stem seals? If you meant guides, have you got an indicative price for this work, figuring its not DIY. Thanks Andrew Bob, The L6 heads are much the same deal as the L4 - I have a feeling that this is going to turn into an essay, writing about playing with heads invariable does. It's always a good idea to get hold of a workshop manual for reference when doing this sort of thing for the first time too. Good quality tools especially the tension wrench make a rough job into a good job. Here's a bit of a technical guide to pulling a head the correct way, i.e. make that the way that an SOB like me was taught to do it on a L engine 30 years ago by one of the best rally teams around. Remove the bits and pieces to allow you to remove the rocker cover - I'll start from there. Remove the plugs and rotate the engine by hand to exactly TDC induction stroke on #1 cylinder; if you go past TDC, then rotate the engine thru 700 plus degrees i.e. nearly twice more to do it again - it's not nice to turn an OHC engine backwards, if we got caught doing it in my learning years it was worth a swift kick up the bum accompanied with a good verballing. When satisfied it's in the correct position, check that valves on #1 are both closed, to be sure you can check that the valves on #6 are open. Note the position of the V in the timing wheel in relation to the notch in the cam thrust plate, the V to the left of the notch is valve timing retarded (possible stretched chain), in the centre is neutral as in stock, and to the right indicates the timing is advanced; Note which position (i.e. P1, P2 or P3) the dowel in the cam is positioned on the timing wheel; factory is Pos 1, if it's anywhere else then it's had the human touch applied to it, i.e. the valve timing has been advanced for some reason sometime in it's past. OK, if the cam dowel is in P1 and notch in centre of the V is as it left the factory and indicates that the cam chain isn't stretched. You may wish to consider using P2 when putting it back together for a small amount of valve timing advance (4 degrees on a L4 anyway, I think the L6 is the same but I'm not absolutely certain of this). Just a word of caution with playing with valve timing on the L6, they seem to be a lot more sensitive to minor advance, if you don't change anything else then things like heaps more grunt mid revs and then absolutely out of breath at 5000 rpm can happen - it's happened to me a few times on carbie fed L26 engines, and by returning the timing to stock it revs to 6000 + as before - could have been just this engine, jury out on that one and I haven't had a L6 apart in 20 years to play some more. Check the position of the rotor i.e. is it pointing towards the front (true #1 position) or the rear (180 degrees out) - useful to know when you're trouble shooting. Collecting this information before you pull it apart gives you a good insight into getting a nicely performing L engine after a head rebuild. Use the trusty old solid wooden chock (don't use particle board and the like) to hold the cam tensioner in place - dimensions are 160mm long, 32mm high along one end and 45mm high along the other - thickness is important too - around 10mm is good. A little trick to aid removal after the wheel and chain is re-installed is to drill a hole in the top of the 45mm end so you can get the tool out - it's prone to sticking so you can thread something fairly strong through the hole eg a leather shoe lace is good (I nearly lifted an engine off its mounts when attempting to get it out once). The straight edge of the chock goes in along the straight guide i.e. passenger side; As a bit of insurance, you can mark a link and it's position on the timing wheel, so you know for sure you re-install it in the same place, providing you don't change the location of the cam dowel in a different P number. Undo the cam retaining bolt and remove the timing wheel from the chain. It's important to keep track of where you remove bits from as everything should be returned to where it came from - this really only applies to head bolts, valve springs and seating washers, collets, rockers etc. Bits like mani bolts etc are not important. Make sure that you know the head bolt removal sequence, on most engines it is the reverse of the tightening sequence as shown on the VRS set. Once you've removed the head then remove each valve, (remember to label or use some method to identify where it belongs), check the valves aren't bent i.e. slide in the guides easily, change the valve guides (always with an old L head as the guides wear), de-coke the valves, check the seats for blow by and correct as required, check that the head is flat and serviceable, by serviceable L series head has all of the letters in "NISSAN" along the lower edge towards the front cylinder visible, if it's on the limit and you need to shave it further to true, then it's head saver time, or better you will need to source another head. Don't forget check that the cam dowel is tight in the end of the cam, grab hold of it with a pair of pliers and check that it's tight i.e. it wont rotate in it's hole and there's no sign of cracking around it where it locates in the end of the camshaft. It's not usually a major problem in a Datto L but none the less they'll grenade real bad if that dowel comes adrift. Re-installation is pretty much the reverse, make sure the surfaces are as clean as you can get them. After the head is torqued down, pay particular attention to relocating the cam timing wheel in the correct or chosen position, as this is the part that ppl find difficult - it's not really that hard if you follow the tear down tips. If it's not in the correct position on an L engine it's going to show up as the engine is turned over during the valve adjustment process. I recommend that the crankshaft is turned over by hand thru a further 720 degrees after completing the rocker adjustments to be sure before the starter is hit for the first time. If you changed the dowel position to adjust the valve timing, it is quite normal to have to rotate the cam a fraction (around 4 degrees for each number) to refit the timing wheel. I would only recommend that you get stuck into the inlet ports if you have had some experience - we practiced this sort of stuff on a stuffed as in cracked or something head to explore the limits and perfect technique. The novice can fairly safely use a dremel and some fine wet & dry to polish the ports, but that's all I'd do unless you are comfortable with delving further. if you're still reading this you will have a bit of an insight into a routine L series head service. Have fun with it, regards Terry -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Bob Sent: Monday, 10 February 2003 9:57 PM To: [EMAIL PROTECTED] Subject: L6 Head Removal/Refitting Hi All, Ive ordered in my VRS kit and will be changing the head gasket shortly. I have only taken a head off once before, are there any special tricks with the L series that I should do? I looked throught the archives and saw plenty of trouble with the chain tensioner slipping, how can I try to avoid that? Also, is it worth cleaning up an E88 head at home with a die grinder, is there anything worthwhile that can be achieved by a backyarder? Regards, Bob --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.ozdat.com/ozdatonline/index.htm http://www.ozdat.com/ozdatonline/listindex.html http://www.mail-archive.com/[email protected]/ ---------------------------------------------------------------------
