What caused this cam Gear damage?

[SLOroadster]

$200 for a head gasket? What planet are you on? $45 from Nissan. I've been working with U20s for about 16 years now. I'd say I know a thing or two about them. I've also been pretty successful with making them reliable. I know for a fact that my engine has held together for a long time while being flogged pretty hard.

I've said my part, nothing more to say. Have a nice day.

Will

[JT68]

Sorry team, I should have said head Set @200+, but if you are going to tear down almost the whole engine, you are probably going to use the better part of a full gasket set so that is probably more...so factor in a gasket set.

[JT68]

Hey Stacy. So I don't like the 170 very much....It isnt a show stopper, and all by itself, I would never tell you to disassemble the engine, but something IS different with that cylinder....As a fresh,really just well broken in engine, it should be in the prime of its life, not have a low cylinder.

Plus we've got all these complicating factors.....Funky drilled sprocket rather than new, prematurely worn chains, worn sprockets,too much chain slack, bent the L out of the way (because he had too much slack) and now the cylinder issue. Not very confidence inspiring when you add it all up.

It's telling me that the previous owner tried to save too much money at every turn with this job...Guessing the valve work needs a touch up on #4, or possible HG issue or something else is amiss. (I think the cylinder itself is least likely unless other corners were cut)

Since you'll have it torn down to some extent already, I'd probably check out that cylinder.

If you are going to remove the head, it really is now a crap shoot. Sorry for the project creep, but I guess you can use that new lift, or do the chains in the car - either way will work.

This basically sounds like a bottom dollar overhaul that went a bit wrong unfortunately.

If you do decide to pull the engine, be sure to plan on at least a clutch disc and bearing, and maybe pressure plate since the PO probably bought cheap stuff there too, ugh. Sorry.

Glad to help whichever path you choose!


j

[svwilbur]

well maybe before I get into the chain replacement project I will do a compression check and see where it is at now that another 35 years has gone by since that last one. make sense? do it now before I can no longer turn it over? maybe they are all at 170 now.....

I need to look up the right way to do a compression check on this engine. I remember something about holding the carbs and dashpots open.
disconnecting coil wire,
cranking until the pressure stops rising, what else?

spark plugs out of all cylinders?
do you have to disconnect fuel line or stop it up?

is there a good write up somewhere?

[Gregs672000]

Um, haven't you already removed the cam gear? I suppose you could just go ahead and reinstall it. Compression is best done on a warm engine, but I'm not sure that's possible at this time (?). Anyway, do pull the plugs, throttle wide open, points disconnected, clutch in, crank as you described.

[svwilbur]

Um, haven't you already removed the cam gear? I suppose you could just go ahead and reinstall it. Compression is best done on a warm engine, but I'm not sure that's possible at this time (?). Anyway, do pull the plugs, throttle wide open, points disconnected, clutch in, crank as you described.

I have the New adjustable sprocket installed with the old chains. I just have to torque it down and I could start it to warm it some and I have to turn it around in my garage anyways. Before I go about replacing the chains I want the roadster turned around with front pointing toward garage door. That way if in the middle of the job I decide to pull the head or the engine I can get access to the front of the roadster easier with an engine hoist. It also give me more working room as the other end of the garage has my Harley stored in front of the Datsun. I can not push it around as my driveway is on a steep angled hill.

So I plan on starting it and turning it around. I could then shut it off and do a compression check.

[svwilbur]

Just an update.... I have done nothing more yet. I have been having my home's roof redone so I have been busy with that.
The roof is now done so I can focus on fixing the Datsun again.
I am ordering parts from JT68 to replace my timing chains and sprockets and the rest of the necessary incidentals.
I hope to start seeing some progress on this in the next week or so once the parts come in.

Before then I will turn the car around and try to compression check it. If it looks bad I may pull the head and have some work done on it.

[svwilbur]

update:

Yesterday I finally started the process of stripping parts off the front end of the roadster so I can get in and replace the full set of timing gears and chains with some great quality products from JT68. it is a bit easier with my new lift as well.

here is where I got to so far. drained coolant, removed radiator, shroud, hoses, fan, pulley, alternator and wires. oil pan comes off tonight.


and yes, I'm going to be real careful trying to remove the water pump studs.

when I get done I may do a more complete writeup of the process.

[JT68]

and yes, I'm going to be real careful trying to remove the water pump studs.

As you and I have discussed, that is really the key to success in doing this job while leaving the head on.

If the pump studs are removed, the cover is much, MUCH, much easier to replace since then you can put it into place under the head and pull it up on to the little alignment dowels.

For those of you doing engine rebuilds this is a good reason to replace the WP studs and use anti-seize compound in the block threads.

Glad you were able to remove them with no drama! j

[svwilbur]

just a quick update and a BIG THANKS to a lot of you. JT68, DAVID PREMO, GREGS672000.....

I got the front timing cover off following JT68 instructions he shared with me on doing it with the head still on. no drama. head gasket still looks ok to me. the cover was bit hard to coax off but it finally came off.

like I said earlier, later I may do a full documentation of the whole process. but right now I just want to thank all those that pushed for me to do a full replacement of all timing sprockets and chains. that was the correct option.

I am not great at telling if a sprocket is still ok or not but looking at the inner jackshaft sprocket it seems obvious to me that this one was not long for this world!
at least it looks that way to me.

Dave Premo even PMed me to voice his thoughts that I should chain them all and that the chains I had on there were basically trash. here is one quote from him:

"I also would worry about the small jack shaft gear I would bet that gear looks every bit as bad as the cam gear."

He basically nailed it! check the last picture out below. His pm along with JT and Greg and others made me decide to do it. But I think Dave Premo's private messages pushed me over the edge. THANKS DAVE! sometimes I need motivation.

when I get the sprockets and chains off I am going to to a thorough inspection of the area. there may be some bits of sprocket somewhere in there. there are some strange marks up between the enclosed area of the head between the upper tensioner and the head gasket just above head gasket on the right side.

here are a couple pics that show the warn inner jackshaft sprocket and other sprockets.

[svwilbur]

apparently back in 1981, about 20,000 miles ago the shop that rebuilt it changed the cam sprocket and the jackshaft chain and cam chain but not the small jackshaft sprocket or the larger sprocket or the crank sprocket. it makes sense now reading the old build sheet but was not obvious just reading the sheet as it said TIMING GEARS and then in hand writing cam gear and a single part number. on other lines it mentions the 2 chains and tensioners and guides. but no other sprockets. I read that as all timing gears but it was just the cam gear. so it was a good thing I took this appart.

[Datrock]

On a positive note, it is nice to know and see that master linked chains had worked great for the 20K miles put on them, especially with running the worn out sprockets, a true test.

[svwilbur]

On a positive note, it is nice to know and see that master linked chains had worked great for the 20K miles put on them, especially with running the worn out sprockets, a true test.

Ha, funny! I don't think I want to test that ever again.

[Gregs672000]

Glad that things are going smoothly, and it looks like it was very necessary. So much better to be sure... Well done.

[svwilbur]

just an update NOT a step by step;

as mentioned earlier I did get the front cover off and aligned the sprockets and marked them and the chains and took the sprockets and chains off and have the new parts to put on but decided to let project creep take a bigger hold on me.

I have a B-cam on the self. it is a regound A-cam. always wanted to put it in as some time I might go with Solex carbs but would like the B-cam already in it. I have been holding off because of the other stuff you have to change out when you change the cam like rockers and lash pads and checking stuff and adjustments.....

But now that we already decided that I needed 4 reground rockers or new ones for the old original A-cam as 4 were showing deterioration, breakdown. with the rebuild that was done in 1981, 20,000 miles ago the rockers and cam were not replaced. so since the rockers were now already off and I needed to get some and wanted some new lash pads as they were showing some wear I decided what the heck lets buy even more rockers and throw the B-cam in and get the right lash pads.

so now I need 8 new rockers and lash pads. but if I get this done I will have all new rockers, lash pads, B-cam, all new chains and set of 4 sprockets. most everything else was replaced 20,000 miles ago, so I should be good for a while maybe.

that was the plan. then I was checking the old cam before taking it off and it is really tight. it should spin easily with your fingers. I can not move it except with some leverage. there are no rockers against it. they were all removed. no chains on it. but it is really tight. so the head may have developed a warp. or something is wrong with the cam stands or caps or it was really cranked down or something? or it got really dry sitting in the garage for a couple weeks as I slowly work on it. im still looking at that. I got pulled away from it.

upside is if it starts spining freely I may have a better performing engine. downside is I may need to pull the head to make that happen. more project creep cause if I do that to get it resurfaced I might as well get valves ground and checked out. and I will need a head gasket set and...... and.... etc...etc....

on the plus side it may be easier to remove and replace the intake manifold with the head out. I have a rebuilt set of SUs I want to swap in that came with an intake.

so im possibly going to be a bit more busy it appears.

this all started as a valve adjustment job.

but I am tharkful for all the help I am getting from JT68. I would not have attemped all this without him. and I am learning a lot and it is fun.