budsaipan Posted November 14, 2016 Report Share Posted November 14, 2016 I have a Z22 block with stock Ka24 pistons on it. Does anyone know if I need to notch the pistons for valve clearance? I've searched and couldn't find any answer to this. I've seen one build thread and didn't seem like that person notched his pistons. http://community.ratsun.net/topic/39329-project-drag-521/page-2 I've also went ahead and put the head on and rotated the cam to check for clearance and it looks like it's hitting the pistons? BTW the valve hasn't been properly adjusted yet. Any info will help. Thanks. Quote Link to comment
datzenmike Posted November 14, 2016 Report Share Posted November 14, 2016 You have to have the timing chain connected to the cam and crankshaft to do this properly. At TDC of the exhaust stroke is the closest the piston comes to the valves. As the piston rises up, the exhaust valve is closing. At TDC the intake is just barely beginning to open and the exhaust is almost closed. As the engine is turned past TDC the piston drops down well out of the way as the intake valve opens. In addition the KA piston does not even come up to the top of the block. It stops 1.55mm below the deck so you have even more clearance, plus the tiny dish. 1 Quote Link to comment
scooter Posted November 14, 2016 Report Share Posted November 14, 2016 If your just turning the cam over, it will hit. If it's timed, probably not, big camshaft? Put some clay on the piston and turn it over and see what your piston to valve clearance is. If you have big valves or a big cam or both you need to check this. 2 Quote Link to comment
budsaipan Posted November 14, 2016 Author Report Share Posted November 14, 2016 Mike and scooter, that makes total sense and your assumption is correct that it's not timed yet. I've just noticed once I mocked the head up, the cam made some scratches from the valve so I got worried. I believe that was the exhaust valve too! I do however have bigger cams Racerbrown 325r so I'll double check but I think I should be ok since I have stock valves. Thanks guys for the quick response!!! Quote Link to comment
Stoffregen Motorsports Posted November 14, 2016 Report Share Posted November 14, 2016 Sounds like you have some engine math to do. If you want to check the piston to valve clearance, try getting some soft valve springs, or mock up springs and install them on the #4 intake and exhaust valves. Put a dial indicator on the tip of each valve and then run the piston up to and then past TDC while checking the P to V clearance on each valve. The cam has to be properly timed to do this. Custom engine building does require some accountability on the builder, so if you are that guy, then it's ultimately up to you to make sure all the pieces you bought fit together. 1 Quote Link to comment
budsaipan Posted November 14, 2016 Author Report Share Posted November 14, 2016 So stock springs should work? Whats the clearance for piston to valve that would be considered safe. Also should I bother checking again for any valve damage since I did rotate the cam while the piston was at TDC? 1 Quote Link to comment
Doctor510 Posted November 14, 2016 Report Share Posted November 14, 2016 0.050" is good if memory serves. Try the clay test, be sure that the timing chain is in place correctly timed. Quote Link to comment
G-Duax Posted November 14, 2016 Report Share Posted November 14, 2016 I always try for .100" on 2-valve engines, just to keep safe from an accidental over rev resulting in valve float. 4-valve engines with smaller, lighter valves, and typically much less valve lift, I may venture down to .060" clearance. And yeah, the modeling clay thing works great, and once you turn the engine through the TDC on over lap cycle, I use a razor blade to cut strait down through the clay to get a cross section of the clearance area. Quote Link to comment
budsaipan Posted November 14, 2016 Author Report Share Posted November 14, 2016 Im just worried that if the valve is damaged from rotating the camshaft wile the bottom was at tdc. Didnt look like it but Ill need to double check once I can get to it. Quote Link to comment
G-Duax Posted November 14, 2016 Report Share Posted November 14, 2016 If it was a minor bump, I don't think you hurt anything, as valves are quite capable of taking a little flexing. But yeah, pull the valve(s), and check them for staitness. Quote Link to comment
scooter Posted November 15, 2016 Report Share Posted November 15, 2016 I second on .100 p to v clearance at a minimum. Cam timing can bounce around with a chain that long. Quote Link to comment
Stoffregen Motorsports Posted November 15, 2016 Report Share Posted November 15, 2016 So stock springs should work? No, I mean really soft springs. Like springs you would buy at a hardware store for making home craft stuff with. A bobble head doll would use a spring this soft. Quote Link to comment
Stoffregen Motorsports Posted November 15, 2016 Report Share Posted November 15, 2016 0.050" is good if memory serves. Try the clay test, be sure that the timing chain is in place correctly timed. .050" is what I would shoot for on a race motor. Same for the street? Sure, why not. 2 Quote Link to comment
scooter Posted November 15, 2016 Report Share Posted November 15, 2016 No, I mean really soft springs. Like springs you would buy at a hardware store for making home craft stuff with. A bobble head doll would use a spring this soft. Like bic pen spring, but big enough to fit over the valve. You can do it without a spring entirely but its a pain in the ass 1 Quote Link to comment
scooter Posted November 15, 2016 Report Share Posted November 15, 2016 .050" is what I would shoot for on a race motor. Same for the street? Sure, why not.Thats pretty tight..... What do you run for piston to head clearance in a race motor? Ive run .030 with success, any less its been mixed, some have had pistons kiss the heads, some were ok... Or if you have a reallllllllllllllly loose motor you could kiss a head even at .030...:p 1 Quote Link to comment
Stoffregen Motorsports Posted November 15, 2016 Report Share Posted November 15, 2016 I usually try to keep the pistons at around .010 to .015 out of deck. With a .050 gasket, that's about what you've got. 2 Quote Link to comment
scooter Posted November 15, 2016 Report Share Posted November 15, 2016 Si senior Quote Link to comment
G-Duax Posted November 15, 2016 Report Share Posted November 15, 2016 Set my race engines up with .030" piston to head clearances, without any problems. Had a 125cc flat track bike that I ran at .016", and it would just start to kiss the head at about 16,000 rpm, and make a huge racket through the cooling fins on the head. It was like an audible rev limit alarm, to tell me when to shift :) Never hurt anything, since the bike always had a forged piston. When the head was pulled, you could always see a light contact mark around the squish area. Quote Link to comment
budsaipan Posted November 16, 2016 Author Report Share Posted November 16, 2016 Nice, alot of great information. Now, since we are talking about valves. What kind of valve spring compression tool do you guys use? I've used about 4 different style and have yet to find one that really works without the cam towers on the way. Wish there was one that I dont have to fight to get those off and on. Quote Link to comment
scooter Posted November 17, 2016 Report Share Posted November 17, 2016 Take the cam towers off and use a standard u type one. Sometimes the keepers can be tricky if you have aftermarket retainers. Quote Link to comment
Three B's Racing Posted November 17, 2016 Report Share Posted November 17, 2016 Unless you know how to realign the cam towers for a smooth rotating cam "Read: No Bind" I wouldn't. You don't need to remove cam towers to remove valve springs. I've used the "C" type valve spring remover before and didn't find it all that difficult. It's your best bet if you don't have the Datsun cam spring tool. 1 Quote Link to comment
budsaipan Posted November 18, 2016 Author Report Share Posted November 18, 2016 Yep that's the reason why I'm worried on taking off the cam towers. I guess I'll keep an eye out for a better tool that works without removing it. Quote Link to comment
datzenmike Posted November 18, 2016 Report Share Posted November 18, 2016 Make something like a claw hammer.that slips under the cam on either side of the lobe the pries down on the retainer with open space to get at the keepers. Quote Link to comment
Stoffregen Motorsports Posted November 18, 2016 Report Share Posted November 18, 2016 It's a job you only have to do once. I've never had a problem with the big, clumsy, C-type. Quote Link to comment
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