Valve stem seals on an L28 motor. Anyone done it?

millsy

4x4 Earth Contributer
Has anyone changed valve stem seals on an OHC motor, like my L28 Nissan motor, without taking the head off?

I am trying to get my head around the steps involved, and even if it is possible. I think it is.

Can I get the springs compressed and remove the rockers without having to pull the cam-shaft out? Have not used a valve spring compressor before! And have not played with timing chains and cam sprockets either. The Holden motors I have played with have been easy with their pushrods and simple rocker gear!

If I do have to take the timing sprocket and chain off, and since I am hoping to be able to turn the crankshaft to bring each pair of pistons up to TDC to do the seals, what would be the sequence for marking the sprocket and chain before pulling it off, and setting it back up for putting it back together, so that these marks line up the first time?

Thanks, Millsy.
 

frosty

4x4 Earth Contributer
G'day Milsy! Are you trying to give yourself an early heart failure? I can just see you now, with a valve spring embedded in your forehead! This is one job, maybe should be left to a pro.
I owned an MQ for years and I must admit, I never took the tappet cover off! (Go on, whip me! I don't care!!) I can only assume, it is the same engine internally as the mighty 120, 180 and 200B engines. Don't touch the camshaft gear until you have driven a stonken big chunka wood into the top of the front end of the timing cover!! (scared yet?) Don't release the spring loaded tensioner on the timing chain. Only then, you can drop the gear and take out the shaft. Make sure you mark the gear, just in case of something. I'm not even gunna ask how ya gunna compress the springs and hold the valves up enough to remove the collets, (circlips) slip the old seals off, put new ones on, reseat valves and springs, replace collets, so and so on.

Sorry big fulla, Gotta say,

send some picy's of the damage! ( forehead!!)
 

millsy

4x4 Earth Contributer
Thanks for the encouragement! I thought someone said it was easy - a guy on the beach at Robe a few weeks ago. He told me he had become an expert at getting the valve timing set correctly on his old MQ, but of course not enough time to go into details while 'on the (beach) run'! More research needed I guess!

I have seen on the web the trick of turning the piston to the TDC and then pushing nylon rope into the spark plug hole as a cushion to stop the valve from dropping into the motor as you pull the collets and springs off etc. Sounds a bit more solid than relying on compressed air!

I forgot about the tensioner issue. But yeah, apparently if you lose tension on the chain, the tensioner tightens up and you can't get the chain back to the right length to fit it all back together. So all I can think of at the moment is you need a helper to pull up on the chain as you turn the crankshaft over from one pair of pistons to the next as you bring them up to the top.

If all goes pair shaped you have to take the timing cover off.

Valve springs in forheads! Hmmmm!

Thanks Frosty!
 

millsy

4x4 Earth Contributer
I reckon I have found the answers to my own questions in this Z car newsletter on the Net - page 10;

http://www.triadzclub.com/z/d/n/2001-12lr.pdf

It is a 'how to' article for changing the seals on the L series of motors. It goes through the whole procedure in detail, step by step. The great thing being that yes, you can do the job without removing the camshaft ( and hence removing the sprocket and managing the chain is not part of the procedure - YEAH ).

So now its a matter of finding the right tool to compress the springs. The one explained in the article, the KD3087, hooks on to the camshaft to provide leverage. It is the best one apparently because it does not jam up against the cam towers.

So any more suggestions or comments, about this method, or any other, are most welcome!
 
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qdlaty

New Member
?

hello, do ya still have this instruction from triadzclub? can not find it. will be good to see how it was done.
regards
qudlaty
 

millsy

4x4 Earth Contributer
Hi qdlaty. No I didn't save that pdf file. In the end I chickened out and decided to just rebuild the motor. I figured it easier to take the head off and put in for reconditioning - new seals and a valve grind.

At the same time of course that gave me chance to fit new pistons, bearings and timing chain, chain guides and tensioner (all in the same kit).

Was quite cheap, and apart from me not picking up on a small depression on the top of the block, on the side of #6 cylinder, and that a previous owner had forgot to refit the oil thrower on the front of the crankshaft (it sits inside the timing cover in front of the oil pump drive gears) the rebuild went well. But quite a lot of time. That didn't bother me. I got a lot of satisfaction from learning how to pull my motor down and rebuild it. Total cost, including all the little things like cans of brake cleaner to clean the parts, pre-lube oil, etc etc was about $1200. ($500 for head reconditioning, $600 for new parts, including the full gasket kit, and $100 for the extra little bits and pieces - kerosene, brake cleanr etc).

As it happened that depression and maybe a worn bearing, or worn shaft in the old distributor, causing bad timing of the spark and hence maybe detonation, cause the head gasket to blow at that point. So two years after I did the rebuild I had to do it all over again. This time was so much easier.

I fitted an electronic distributor at the same time. One of the best things I did. Amazing how smooth a motor runs with a decent dizzy! I can give you a circuit diagram I drew up if you want one. I designed a circuit and incorporated a double pole triple throw switch so that the old dizzy can be put back easily if the new one lets me down on the tracks. The middle throw gives an immobilizer effect.

The first time I had a seized head bolt. It had seized in the alloy head actually, and I ended up snapping it off flush with the head. I spent hours trying to get that bolt out before it finally snapped! On the second rebuild the bolts came out so easily, because I had made sure I put a bit of silver anti seize past on the threads. When I put the head on the second time I actually bought a new set of head bolts from my local fasteners business. They only cost about $40 compared to about $400 for genuine Nissan bolts! But since they were not exactly the same length as the originals I had to make very sure I tapped out all the sediments at the bottom of every bolt hole in the block, and did a lot of careful measuring up so I was sure the new bolts had both a good penetration inot the block, but not so far that they bottomed out!

The MAIN IDEA I really want to get across is that the reaon my motor was blowing smoke on take off, and using large amounts of oil (in the end it was up to 1 litre of oil per 300km!) was not the valve stem seals at all. It was the oil control rings. They had all seized up, or cooked solid, into their lands. You could run your finger down the piston skirt and they were perfectly flush with the piston surface, and glued solid. So no oil control, and oil getting up to the combustion chamber very easily!

I saw lots of similar pistons inn a forty four gallon drum at the engine workshop. I reckon every piston I plucked out of that drum had the same problem - seized oil rings.

So I think you might possibly/probably have the same issue.

If you like tinkering with motors, or never tried it, I recommend the experience. Don't rush. Treat it as a learning experience and as a hobby thing, like building a model aeroplane, or piece of furniture. If you have that sort of mind set, rather than 'I have to get this thing fixed as fast as possible', it is a great thing. Otherwise you might be heading for headaches and stress. Hope it's not your daily drive!

Here are some of my experiences, and pics, of my rebuild.

http://www.4x4earth.com.au/forum/motors/6738-few-photos-l28-rebuild.html

As far as removing and replacing stem seals without pulling the motor apart, I had trouble finding where I could purchase that tool. In the end I bought something, but when I tried to use it I was not happy with the process. It was very difficult to apply the required force, in an awkward position for my old back, and hands that are not as young and stron as they used to be. Maybe if I persisted it may have worked.

I actually had to compress the springs a bit to pull the cam followers off and refit them when I pulled the them, the the cam towers and the camshaft off the head. All I used was a lever, in the form of a an old tool. It was square section rod of hardened metal with a chisel like wedge end at one end. I just put it under the cam shaft, rested on the roughened section between polished lobes, and used that as the fulcrum. The end of this tool was pressing down on one side of the spring cap/plate. I had to pull up fairly well because it was only about 25cm long. If I had used something more like 35 or 40cm long it would have been easier, with the greater leverage.

So I am suggesting that if you are happy to pull the cam followers off first, then use a lever, to compress the spring to get the collets off. Maybe even a long open ended spanner would be just the thing!

Of course the other issue is you have to make sure that you bring the piston up to TDC so the valve does not fall intothe cylinder when yu release the collets. For this there are two methods apparently. Using compressed air, or poking a good length of rope in through the spark plug hole.

You can look these methods up on the Google.

The other thing I was afraid of was fumbling the collets. I guess you can easily by spare if you drop one down the side of the motor. But you might consider blocking off the oil drain holes at the back of the motor, and the big hole where the timing chain comes up at the front of the motor. Probably won't do any damage swimming around in the sump oil. But you never know!

Let us know what way you decide to go - engine rebuild, or valve stem renewal.
 
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qdlaty

New Member
well..:)

frist- thank you so much for such a full reply. its more that I could expect.
second- its quite late in Poland to take write decision what to do, or steams or whole engine:)
third- I didn't introduce my self in wright way. honestly speaking I didn't expect any answer at all:)
so I do now, to have a basic view who am I:

CZTERY LAPY KUDLATEGO qudlaty=qudlaty= kudłaty=> means shaggy:) rest you will see.

tomorrow will write more.

"sprzedam" stands for " for sale" - this is my beloved l28...
 
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