Datsun Roadster Forum-311s.org

Hi gang, so I'm reassembling the engine and it looks like I had some timing chain movement while spinning the engine around on the stand, cleaning up etc. if this can be confirmed. I had marked my chain and cam gear with a sharpie before disassembly, but things are now not what I expect. Here's what I don't know and need input on:
When the engine is on TDC per the pulley (as in the picture) I would assume that the cam locating pin should be straight up, bolts at 90/270 degrees, YES?
If I put the cam gear back on per the sharpie mark, it's way off vs if I rotate the cam gear back 1 tooth, then it's perfect (see pics). The only thing I have to go with for the crank gear location are the timing marks, which I did following a method and using a dial indicator etc when I built the engine before, so I'm pretty confident 0 is pretty darn close to TDC. Unfortunately I cannot see the gear itself let alone it's marks. One option would be to pull the crank pulley to observe the key, but I'd rather not if it's not necessary.
When using the sharpie mark to locate the cam, if I rotate the crank to put the cam straight-up the crank timing mark moves to 20... that cannot be right. Other info that may be noted: I'm using thicker head gasket, however I don't think this would change things this radically as the chain length is the same of course.

So, if someone knows from experience, has pics or can rotate their own engine (probably needs to be out) to reflect how it should be and report back, I would be forever grateful!
Pics: Crank pulley, cam aligned with sharpie mark, cam rotated back one tooth. All input welcome!

Would counting the links help? I think that’s what I did when I replaced my chains last year, and it came out just fine.

I guess from reading your description more closely, that you can’t see the chain fully. But based on the diagram I just posted, your sharpie mark looks to be right as there should be a full link at the dot on the cam gear.

Thanks for responding Matt. I have the diagram. Regarding the chain links and the cam assembly mark, properly installed you would be right, but you can roll the chain one tooth and it will then be in the middle of a link, so it's not really relevant if I rolled the chain on the jack shaft gear one tooth, which is what I suspect happened.

To help make this more clear, what I need is an engine to be set at TDC OR 0 on the crank pulley and then remove the cam cover and tell me if the cam pin is straight up. If it is, I'll take that info as a reference to where the crank and Jack shaft gears are and install the cam gear accordingly.

Hey Greg, just a couple of observations. On the crank harmonic balancer pic, the red line at TDC seems to be off the grove and the distance to the next line seems wider than the other (spacing). Also, my harmonic balancers don't have the dogs/teeth behind the pulley (?).

On the chains, you can line up the silver links with the timing marks/dots on the cam and crank sprockets (not necessary) but might help as they set the correct number of links. Lastly, as a check at TDC, the crank woodruff key should be straight up.

When I replaced my chains, the cam gear dot is straight up and the 90 degrees Clockwise dot is in the middle of the link. I put the silver chain link at the 90 degree position and the other silver link lines up on the crank timing mark. I have pics somewhere and will post it if I find them.

The 'dogs/teeth' behind the balancer look like the trigger wheel for a Hall effect (or optical) crank-fired ignition.

Correct on the teeth... crank fired.
Thanks guys. I know where the chains should go when assembling (links in proper places, etc.). What has happened (I believe) is that the chain rolled one tooth. I did not observe this happen and I had my chain supported though it did become unsupported at one point, and what I'm seeing does not make sense when I reassemble it. For function, the chain itself does not care what link or position in the link the asembly mark its on.

What I need is a picture of the front WITH THE FRONT COVER AND CRANK PULLEY ON and the engine turned to TDC or 0 on the crank, then an image of what the cam gear pin looks like... I suspect it is straight up. I'm trying to avoid having to pull the front cover (which I just resealed) and potentially damage a $230 head gasket, or remove the head!
Thanks!

That hoist hook placement makes me say yikes

If the lower timing chain has not moved (and it can't unless you pulled the chains) they will still be lined up correctly. The cam mark for stock timing should line up at either 3 or 9 o'clock. Since you have an adjustable timing gear, that could be a little off. As for the chain being off a tooth, its kinda irrelevant since the lower chain hasn't moved. Simply adjust the gear in the direction required and do your cam timing accordingly. The upper chain could move 20 teeth, but as long as your cam is at 3 or 9 o'clock at TDC, that is what matters. Obviously you will adjust the cam to either advance or retard it, so the gear mark will end up somewhere close to the stock 3/9 oclock, but not exactly spot on (Or the crank will be slightly off from TDC with the cam at 3/9 o'clock.) As long as the lower chain hasn't moved, the upper one can move back and forth all it wants, and it won't affect anything as long as the cam is in the correct location in relation to the crank. No, the shiny links won't be exactly right, but that is assuming you have a couple shiny links in the chains. (I don't) Just rotate the gear backward a tooth and everything should be roughly where it should be. CHeck with a degree wheel to make sure things are where they belong.

Will

Thanks to all who reviewed this post! Based on what I can see in the photos provided by Joe, after talking to Dean who was nice enough to call me this morning, and reviewing all schematics (Matt) and confirming what I know about these chains and gears (Will) I'm confident that I must have allowed the chain to roll off the jack shaft gear one tooth.

Note that the pin in the cam gear is locating the cam, so it's not being used as an adjustable gear right now and is not part of what we're seeing. There are no rocker arms installed so it's easy to turn the cam.

Joe, regarding the timing marks on the pulley, the timing mark I'm most concerned about is 0, as I now set the timing with the computer and I needed true TDC. The other marks were older and more reference marks to confirm how much it's advancing or that it's advancing normally, which I confirm with a timing light.

I still welcome a pic or two that mirror mine, with the engine at TDC on the cover timing pointer, and the cam cover off showing the bolts/pin. I'll sleep better.

Again, verify your TDC, if need be, use a pencil through the spark plug hole to find it. Your lower timing chain can't move unless you removed the tensioner and walked the chain to a different tooth. Assuming that was not done, the relationship between the jackshaft and the crank has not changed. Only the location of the chain links on the upper chain have moved, and/or the rotation of the cam. You still need to verify that the cam is timed correctly using a degree wheel, and/or a dial indicator on the cam lobe.

I might get around to putting the head back on my engine this weekend. I didn't touch the lower chain. I'll take some pics when I do.

Will

Greg, put your crank at TDC, cam gear bolts @ 3 and 9 oclock, pin hole straight up, with drivers side of cam chain tight. Good to go. Pat

Thanks again to Everyone! I've been working on and assembling the motor all day, and it's all buttoned up and almost ready to install (clutch and transmission left). I'm confident on the crank and cam timing issue. I've just never had a chain slip a tooth, but the old wood chain support I always used was a bit worn out, so I made a new one and that one did pop out unexpectedly but I thought I'd caught it... Apparently not. With crank at TDC the cam is correct (3 and 9, pin up) when set one tooth back from my original mark. The engine spins over without issue, smooth and easy. One unexpected but logical change with the thicker head gasket is that I no longer need any shims on my upper chain tensioner, and the chain is just right.

I spent a lot of time checking and modifying the crank scraper to make sure it never hits anything... frankly a lot of work (2 days) for a questionable potential for improvement. Not what the typical owner would be willing to do I think. Nevertheless it's in, sealed up and good to go. I expect to have the engine installed and running, likely on Saturday.

Woo! Good luck, Greg!

So I got the engine installed and running today. I took a pic of the front of the engine, everything was right. After getting past a couple injector wiring connection problems (had one in the harness come disconnected so it was running on 2 injectors) it fired right up and it didn't take long to balance everything and get the idle right. Revs smooth, but I'm sure it will need some tuning. I'll do some testing later. So far no oil leaks, temp fan kicked on when expected, engine sounds great.