z-ya Posted February 3, 2003 Share Posted February 3, 2003 Anyone know how much slack on the timing chain "slack side" is acceptable? I'm using hole #1 on the cam gear, and the timing marks seem to be OK (they overlap). But it seems like there is a lot of slack. The head I'm using may have been milled. I know it's been posted before, but what is the stock head height? I'm using a stock head gasket. The timing mark on the cam tower lines up with the one on the cam gear like this: I'm not sure about the miles on the chain, but the engine it came from was spotless, and had very little wear. Any info appreciated. Pete Quote Link to comment Share on other sites More sharing options...
DAW Posted February 4, 2003 Share Posted February 4, 2003 What sprocket hole you put the cam dowel in is not going to change the amount of chain slack; it only compensates for it in the timing of the cam. The guides can be adjusted, and if it's still too loose then you're chain is stretched or you need to shim the towers. DAW Quote Link to comment Share on other sites More sharing options...
z-ya Posted February 4, 2003 Author Share Posted February 4, 2003 Does anyone know "how much" play is acceptable on the slack side? I have new guides, and tensioner installed, so the chain is tight on the tensioner side. Pete Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted February 4, 2003 Share Posted February 4, 2003 The tension is applied with the little shoe at the base of the curved guide. You cannot set the tension, oil pressure sets the tension. Your best bet is to align the guides as best you can to the chain, assuming the tensioner is applying pressure, then tighten the guides. The oil pressure tensioner should then be set to go. Quote Link to comment Share on other sites More sharing options...
DAW Posted February 4, 2003 Share Posted February 4, 2003 There are two sets of holes for the (right side) guide. Assuming you've already set it up to take up the most slack, and realizing that the tensioner keeps tension on the chain but won't significantly change the line of the chain as it runs, if you're setting up the cam in hole #3 and the cam is still retarded per the notch it means the chain is stretched/sprockets worn or the distance between the camshaft sprocket and crankshaft sprocket is smaller than stock (due to milling of the head. Standard head thickness is 4.218 in. DAW Quote Link to comment Share on other sites More sharing options...
z-ya Posted February 4, 2003 Author Share Posted February 4, 2003 Thanks Katman, This motor will be used for autocross and time trials, so I want to be sure. Right now the slack side has almost an inch of slop in it. Too much if you ask me. I'll need to measure the head, and then go from there. I may just throw a new chain and sprokets in there. Pete Quote Link to comment Share on other sites More sharing options...
DAW Posted February 4, 2003 Share Posted February 4, 2003 Sorry, I got that figure from my '72 Nissan 240Z factory service manual. Sounds like there's too much slack and considering the stresses of racing, why not just buy a new chain? Cam timing is too critical to have it jumping around. Maybe you can go to a parts store and hold your chain up to the new one...if they are the same, then change your mind about the purchase. DAW Quote Link to comment Share on other sites More sharing options...
z-ya Posted February 5, 2003 Author Share Posted February 5, 2003 I think I got it figured out, correct me if I'm wrong. When you time the cam, you need to install both guides, and the tensioner. Now if the cam is slightly off, but the crank is still at TDC, then there could be significant slack on the slack side. So what I did was, turn the cam slightly untill there was minimal slack on the slack side (the tensioner takes up the slack). I checked the timing marks, and they didn't line up, so I moved the chain and sprocket to the number 2 position (following the same procedure), and wha-la, the marks line up perfectly , and no slack. The tensioner is sticking out about 1/4" from it's holder. Should be OK (I hope). Pete Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted February 5, 2003 Share Posted February 5, 2003 The cam timing is done with the tight side, the slack side should not enter the picture. If you turn the crank clockwise to TDC, the notches on the cam gear and the tower should line up. Hopefully the tight side guide is not interfering with the process...maybe install the slack side, but time the thing first, then install the guides? Quote Link to comment Share on other sites More sharing options...
katman Posted February 5, 2003 Share Posted February 5, 2003 Originally posted by DAW: Standard head thickness is 4.218 in. DAW Uh, that'd be 4.248 and most virgin heads measure closer to 4.251. We usually mill the slots for the 4mm bolts in the curved guide out a little extra so we can use a pair of channel locks to squeeze the curved guide toward the straight guide and lock it down so there's virtually no slack in the chain for ITS racing motors with heads milled say 0.010 to 0.020. For a virgin thickness the stock slots in the curved guide should suffice. We don't rely on the oil pressure from the tensioner, and you don't want the chain flopping around because it does all sorts of nasty dynamic things to the cam and valve train forces. How much slack is kind of a touch thing. If you rotate the crank backwards a smidge to make the slack on the side with the straight guide, there should still be a little tension there, the chain shouldn't be loose. Quote Link to comment Share on other sites More sharing options...
jeffp Posted February 5, 2003 Share Posted February 5, 2003 First of all, any chain you put on your engine is going to stretch in a very short time, so buying an ew chain will have a short lived life in regards to how long it is. When you install the chain and the quide assemblies what you should do is this. The right side quide is strait and that is fine in all cases. You install the sprockets and the chain, then you turn the crank clockwise to tension the chain. Then you install the right side quide, and adjust is so it is just touching the chain, but not pushing on the chain. If the quide will not adjust to just touch the chain, then get a file and elongate the mounting holes so it is aligned perfectly with the chain in the top of the quide and the bottom of the quide. Then without turning the engine, install the left quide so that it is just touchuing the chain also. If the chain is lose then push the hydrolic adjuster out with a screw driver to tighten up the chain and make the left side adjuster so that it is just touching the cahin as before. You dont want the adjuster to push on the chain as all that will do is wear a groove in the rubber on the adjuster until it finds its adjustment, so if the adjuster is just touching the chain the wear on the guide will be very minimual and that will be fine. Regarding the notches on the gears and back plate. I was not happy with the three holes to adjust the notches, which BTY may not be the corret cam timing for the cam anyway because of the slight lose fit with the mounting bolts on the back plate, so I bought an adjustable sprocket from HKS, not the nine hole sprocket from motorsports, so that I could put a degree wheel on the crank and use a dial indicator to get the cam dialed in exactly. That is really the only accurate way to do it, but the notches in almost all cases gets the cam timing good enough to run it that way. When you start getting a custom grind cam, that you have set the lobe centers and the intake opening and closing, and the exhaust opening and closing data, the cam timing becomes critical as a few degrees will affect the cam significantly. so if you really want to do it right, get a degree wheel and dial indicator, take your time and make sure the timing is correct to the grind specs, and then you will be able to know exactly what that particular grind does for your engine. Just my O2 here guys Quote Link to comment Share on other sites More sharing options...
z-ya Posted February 6, 2003 Author Share Posted February 6, 2003 Jeff wrote: If the chain is lose then push the hydrolic adjuster out with a screw driver to tighten up the chain and make the left side adjuster so that it is just touching the cahin as before. You dont want the adjuster to push on the chain as all that will do is wear a groove in the rubber on the adjuster until it finds its adjustment, so if the adjuster is just touching the chain the wear on the guide will be very minimual and that will be fine. First, I assume left is passenger side, right is driver side (USA). When you say adjuster, are you talking about the curved guide on the passenger side? I can't see how the sping loaded tensioner cold not touch the chain. Thisis the procedure I used. I set the crank to TDC. I calibrated the timing marker to TDC before I put the head on, so I put the timing cover back on momentarily with the damper to set the crank at TDC. I then put the chain and spocket on, and snug the sproket bolt. I then turn the cam counter clockwise (from front) until there is no slack on the driver's side. I do this because I don't want to move the crank from TDC. I then look at the timing marks on the cam tower and sproket to see if they align. If they don't, I take the sprocket off, and go to the nxt number for the chain and sprocket. Hole #3 on mine shows perfect alignment of marks, so I think I might replace the chain and sprockets. Or should I just use the one that is good and stretched? An adjustable sproket is not in the budget (unless someone knows how to make one , I've got machine shop access). Pete Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted February 7, 2003 Share Posted February 7, 2003 If you line up well on #3 (I've never had a motor much past #1), personally I'd replace the chain. It's getting close to the service limit. Quote Link to comment Share on other sites More sharing options...
Guest norm[T12SDSUD] Posted February 8, 2003 Share Posted February 8, 2003 If you replace the chain, now would be a good time to upgrade the curved guide bolts as well. I have broken them in two thru high rpm drag runs at least three different times. I can't remember the exact measurement, but I know I went up to a 2mm thicker bolt than the stock bolt by drilling and tapping a new bolt hole. Hopefully that will cure any future bolt shearing problems. Oh and btw I had a new chain so they didn't break from chain slap. Later,norm Quote Link to comment Share on other sites More sharing options...
DAW Posted February 8, 2003 Share Posted February 8, 2003 OK, I think that there are ways to know crank position @TDC without putting the timing cover and damper on each time. I believe the crank key points straight up at TDC. You can check by doing it the way you have been and confirm. If not, there is a crank sprocket mating mark that you could reference by putting your crankshaft at TDC, bend a coathanger pointer (bolted to the block) point exactly at the reference mark, and you have it. This will save a lot of time and is important for an accurate set-up because the crank needs to be brought just to TDC while turning clockwise and maintaining steady tension on the chain. If you pass TDC, you have to start over with another pass. Anytime you reposition the cam sprocket to another hole you need to do this smooth, steady pull technique to check the result. DAW Quote Link to comment Share on other sites More sharing options...
z-ya Posted February 10, 2003 Author Share Posted February 10, 2003 Put a new chain in today, and timing marks line up perfectly using #1 marks. Only about 1/8" of the tensioner shaft visible. All set to go. Thanks everyone Quote Link to comment Share on other sites More sharing options...
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