Datsun Roadster Forum-311s.org

I recently had my U20 motor rebuilt. Yes I am new to this site. I've owned my roadster for a long time, and could assemble this motor. However, I had a good mechanic do it for lack of time. Everything is perfect except that the timing chain rattles quite a bit. It is getting plenty of oil pressure to the tensioner. he tried using the old unit after the new one didn't tension up. Still not working. We cranked it over with the tensioner off, and plenty of oil comes out. Obviously one would suspect that the tensioner would be plugged, not so. It isn't the gasket blocking the hole either. However, we must be missing something obvious because this system is so simple. Everything is mounted correctly. I have a spare motor with a chain that rattles. And aquantences of mine have had the same experience. Is this system real touchy? Does anyone insert a strong spring to supplement the tension? Many Thanks.

I would say your head has been cut enough that it is affecting the timing chain via the cam tower height. You can purchase shims of varying thicknesses from one of the vendors to take the slack out. You should not have any rattle with a freshly rebuilt motor and a new timimg chain. Too bad they did not make the U20 like the L series where you could rotate the cam shaft timing gear to remove the slack. Good luck!

Steve

I hear what your sayin. And I pondered this. Now I remembered one important thing: My friend ran the motor breifly to see the tensioner pumping back and forth. This would tell me that it's not doing it's job. Thanks for the timely reply, your advise won't be disregarded. Any thoughts?

Tony do not disregard the Cam tower height, too many machine shops, and engine rebuilders do not understand the significance of the Cam tower height in proportion the timing chain and the whole timing system. Talk to whoever did the work on your car, ask them if they shaved the head at all, if so how much, put in shims accordingly.

Second, there is a temproary fix for your problem if you still think its the tensioner, by a piece of 5/8" i.d. (inside diameter) nylon tubing The O.D. is not too critical 1" will work. Cut a piece at least 3/8 in length depending on how much slack is in the chain, taking the tensioner off very carefully, making sure you don't drop anything in the engine (I use either a wire or a plastic zip tie, to hold the tensioner closed) put the piece of tubing behind the tensioner to stop it from going back. This will work until you have time to get those cam towers checked.

Lou

True that! Many thanks for the replies.

Stock head thickness is 4.528" You can shave up to .020 without having to shim the towers - any more than that and you really should shim them. Any time you shim the towers you need to check the cam lobe wipe pattern on the rocker arms. .020 shims caused no problems on my engine but more than that and you may need thicker lash pads to keep the cam from falling off the rockers - just be aware of that. Worn gears will add to the sloppiness too - look for pocketing in the valleys if the gears weren't replaced.
When is it rattling? At Idle, you really don't have that much oil pressure in their to keep the tensioner tought. That's the reason for adding the washers or spacer to the tensioner pistion. Gordon Glasgows site has good instruction on this as well as a copy of the rising sun racing archieves which are worth looking at for tensioner info. I think there's a link to Gordons site from the 311s links page.

I'm very grateful for all the attention. I just wanted to also say that everything is new. Gears, camshaft, chains, and tensioner. As well as pistons, rings bearings, oil pump etc... If the previous chain didn't rattle, asuming that the machine shop took no more than 20 to 30 thou off, would shimming the cam towers make that profound of a difference? Keep in mind that plenty of oil is getting to the tensioner and the gasket isn't pluging the hole. I understand the some people refer to shimming the tensioner with a nylon tube as a temporary fix. And some people don't make a refrence to this as being temporary. I'm going to feel foolish if this is something very elementry. Thanks.

Those shims are a real big deal for taking out any slack in the U20 upper timing chain. Your head has to be cut some to have the amount of slack you are describing. I would not use the temporary fix on a brand new motor. Shim the cam tower with the proper shims and you should have no further problems. Do you know what the head dimenions are? Are they within the lower limits?That will give you an idea of the shim size. If your head is shaved too much you will have more problems than a loose upper timing chain. I have seen people use strap ties to hold the top tensioner out on an older motor to take the rattle out. That is why I am an R16 stroker kind of guy. The U20 is a solid motor but I just dislike the timing chain setup with that jackshaft in the middle. They are rockets until the chains get stretchted-they then become potential shrapnal makers. My 2 cents any way.

Steve

Come on Steve, live a little! Shrapnel isn't so bad (as long as you have the proper armor!!)

I agree. It sounds like either the head has been cut or there is something goofy afoot with the chains.....

Sid,

Maybe some Army Surplus kevlar would do the trick!! 1500, 1600, stroker, 2 liter, Ka24, SR20 or what ever else someone stuffs into the engine bay-- these cars are a blast to drive.

Steve