Nigel Posted August 5, 2008 Share Posted August 5, 2008 So, I'm aware that a slipping harmonic balancer pulley can be an issue, and I'm pretty sure my pulley has slipped. But I wanted to get some other opinions on the symptoms I'm seeing. I'm running an L28 Turbo in my 240Z with the original L24 pulley that came with the car. I have an SDS EM3-6F system with the trigger magnets mounted in the rubber damped part of the balancer. What I have noticed: 1. Fuel economy seems down. I haven't done better than 21 mpg on the highway this year, but I have a receipts from last year with one indicating a best of 24mpg (mind you, I'm running a 240SX 5 speed this year, with a slightly shorter 5th than the '82 280ZX box it replaced). 2. Full throttle acceleration feels a little flat. 3. Two or three times when starting the engine, I've heard a very brief chirp, kind of like a slipping belt. But the belt appears to be tight (takes some effort to twist it 90 degrees) 4. The idle timing has always been set to 20 deg advance, but I've noticed that idle speed and smoothness significantly improve when I crank the timing up to ~28 deg or more advance. 5. I bumped up all the timing values by 10 deg and acceleration seems crisper, and EGT's cruising on the highway have dropped by at least 50F. Fuel economy hasn't improved though. I realize that the best way to determine if the pulley has slipped is to set the engine at TDC and check the timing mark, but I'm not sure how quickly I'll be able to get around to doing this (is there a quick and dirty method I can use?), and I don't want to delay getting the necessary components together to replace the balancer. The most telling evidence appears to be that I can run 28 deg or more advance at idle, and the engine actually runs smoother. I cranked it up as high as 40 deg advance at idle and much to my surprise, it didn't seem to make much difference. I would have thought that there would be a point where it starts to run noticeably rough again. Regardless, I've never tried cranking up the idle advance before, so for all I know, this could be normal. In the mean time, I've painted alignment marks on the balancer so I can see if the pulley does indeed slip at some point in the future. Any insight would be greatly appreciated! Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
bobbyc Posted August 5, 2008 Share Posted August 5, 2008 iwould check asap...if your pulley is slipping...that means your crank is gonna be fubarred...as the key is likely torn from the crank, unless you are saying the pulley is seperating. aslo...a good way to check for the correct tension is to press the belt down in the middle betweem to pulleys.....it shouldn't give more than a 1/4" Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 5, 2008 Author Share Posted August 5, 2008 iwould check asap...if your pulley is slipping...that means your crank is gonna be fubarred...as the key is likely torn from the crank, unless you are saying the pulley is seperating. aslo...a good way to check for the correct tension is to press the belt down in the middle betweem to pulleys.....it shouldn't give more than a 1/4" Sorry, I should have clarified that I'm talking about the rubber damped pulley slipping on the harmonic balancer hub... Nigel Quote Link to comment Share on other sites More sharing options...
Clifton Posted August 6, 2008 Share Posted August 6, 2008 Check your timing. You should know what it was before, if not it should match what the SDS prgrammer says. If it doesn't, it moved. I have had them move before, Both times itwas more than just a slip. You should be getting better than 21-24 though. I got around 27 on my last highway trip running 75+ on a decent tune. What's your cruise timing at? Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 6, 2008 Author Share Posted August 6, 2008 Check your timing. You should know what it was before, if not it should match what the SDS prgrammer says. If it doesn't, it moved. I have had them move before, Both times itwas more than just a slip. You should be getting better than 21-24 though. I got around 27 on my last highway trip running 75+ on a decent tune. What's your cruise timing at? Well, I thought about checking the timing, but I don't think that will tell me anything. The timing mark and the trigger magnets are on the same pulley, so the timing will probably look correct. Unfortunately, my timing light is at my father's place 250 miles away, so I can't verify that. The only way that I can think of to know for sure if the pulley has slipped is to set the engine at TDC and see if the timing mark on the pulley matches the 0 deg mark on the timing indicator. But there's no really simple way I could find to do that. I was going to see if I could get a rough idea of where TDC is by putting a rod through the #1 spark plug hole and trying to find the point where it sticks out the most. I realize there are a few deg of crank rotation where the rod won't move, but if the 0 deg mark is significantly off that should tell me what I need to know. As for my timing curve, I was starting with 20 deg at idle, and ramping up to 38 deg by 2750 rpm. AFR's crusing at 75mph are low 15's. I do remember my mileage being much better than even the 24 mpg I got last year, but I don't have any records prior to last year. The engine feels great otherwise, so I'm not sure why it's so bad now... Nigel Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 6, 2008 Share Posted August 6, 2008 This is one of those things you mark down in your head after the first time it happens to you (for me it was 1979 on a 1969 Corvair Monza...) PUNCH A REFERENCE MARK ON THE FACE OF THE PULLEY BETWEEN THE CRANK PORTION AND THE DAMPNER PORTION. This becomes a simple matter of checking with a mirror and your timing light every time you do a tune up (if you mark concurrently with your given timing advance mark...) I know when I sent my Monza's pulley off to Dale Engineering (er...now I hear they do Datsun Pulleys too! Imagine that, crossbreeding! LOL) when I got it back I filed that slot to MAKE SURE I knew if it slipped again! Too late for you now if it's slipped, but going forward, if you grab a JY pulley MARK IT before installation. And yes, a chirp on startup can be the harmonic slipping. Chances are if it IS slipping, filing the mark will show you if it's bad pretty shortly. If you loosen your accessory drive belts, and firmly grab the pully with both hands, sometimes you can feel it slipping/moving. Some times the only thing keeping it from spinning freely is the tension from the alternator belt---I know that's what it was on my 81ZXT engine! So that's probably the most effective method given your current circumstances: Loosen or remove the belts and crank on the pulley with your hands and see if it's slipping. It should be pretty obvious. And if it's 'moving' but not 'spinning' you know the elastomeric is shot to the point of failure---you shouldn't be able to move it at all with your hands. If you can't move it...you're safe: PUNCH MARK IT and then you won't have to pull your belts again to check! LOL If it's slipping, it's not good for the crank---it does perform a torsional unloading of the crank snout---without it working there are torsional stresses on the crank that aren't good. Good Luck. Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 6, 2008 Author Share Posted August 6, 2008 Thanks Tony! I'll give that a try. I ordered some replacement magnets from SDS last night just to be safe. I know where I can get a new Euro pulley locally, but cash is pretty tight right now, so I may end up just getting another used North American one. Fortunately, I kept my magnet template from when I first did the install... Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 6, 2008 Author Share Posted August 6, 2008 Well, I just tried moving the pulley by hand, and it won't budge. However, I can only get at it with one hand, due to the electric rad fan and intercooler plumbing, and I can't get much of a grip on it. So, I'll have to label this test as inconclusive. I think the only way I'll be able to tell for sure is to set the engine at TDC... Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
blue72 Posted August 18, 2008 Share Posted August 18, 2008 That's what I'd do, get it to TDC and check if your timing marks on the damper line up. You could either do the piston stop method, or you should be able to look at where the lobes on the camshaft are pointed to get a ballpark estimate on how close to TDC you are as well. Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 18, 2008 Author Share Posted August 18, 2008 I was able to extend the plunger on our dial gauge at work, and get it down the #1 spark plug hole. As best I could measure, it looks like the pulley mark is only off by 3 degrees, or a bit more. That could be the manufacturing tolerance. I've bumped up my base timing by 5 deg across the board, so I'll leave it at that for now. I need to get a timing light on it to see if I set the SDS timing right to begin with. It was 7 years ago that I first did it, and I've never double checked it since. I just need to find the time to visit a buddy with a timing light... Nigel Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 19, 2008 Share Posted August 19, 2008 Just make a couple of punch marks where you can get to it and see them... If it slips you can tell with a mirror and torch, easily and quickly! Quote Link to comment Share on other sites More sharing options...
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