ZackeryNM Posted October 6, 2011 Report Share Posted October 6, 2011 So if i give you like say five bucks you'll turn my truck into this? jk nice. job well done! Quote Link to comment
ZackTheImpaler Posted October 25, 2011 Report Share Posted October 25, 2011 Is it bad that I'm posting just to bump this up, because this thread has like every comprehensible answer to a 720 question a noob could ask? Swear it should be pinned by now haha Quote Link to comment
Sealik Posted October 25, 2011 Author Report Share Posted October 25, 2011 Is it bad that I'm posting just to bump this up, because this thread has like every comprehensible answer to a 720 question a noob could ask? Swear it should be pinned by now haha I have to come clean....................................I've been seeing other threads.... :lol: Most likely finish them here though.... Moar Shit...... :) Quote Link to comment
Sealik Posted October 25, 2011 Author Report Share Posted October 25, 2011 Pulled the motor.....head......No 1 piston Rod bearings are worn and piston skirt has wear...scuffs. Measured the piston (cleaned the crud off) the best I could with digital calipers. Stuck them over the top...down to the oil rings. Pistons....approx...88.88 Bore.....approx....88.38....that's .4mm /.016 inch difference :blink: Removed top ring from piston (managed to break No 2 ring :D )...slide it into bore about an inch down...gap is .012 Not sure about this...???..but the piston pin is not centered in the piston....a good 1/8 off. So...the ring gap is within specs...but.... Quote Link to comment
datzenmike Posted October 25, 2011 Report Share Posted October 25, 2011 Measured the piston (cleaned the crud off) the best I could with digital calipers. Stuck them over the top...down to the oil rings. Pistons....approx...88.88 Bore.....approx....88.38....that's .4 difference :blink: Your piston is larger than the bore. A 0.4mm is 0.015"/2 = 0.0075" clearance all the way around the piston to the wall. Supposed to be 0.001" to 0.0018" by the FSM for '84 720. At the moment that's almost 4 times past the maximum clearance. What does the bore look like?? Removed top ring from piston (managed to break No 2 ring :D )...slide it into bore about an inch down...gap is .012 Not sure about this...???..but the piston pin is not centered in the piston....a good 1/8 off. Top ring gap is 0.0098 to 0.0157 so your 0.012 is in the middle. The pin should be able to slide sideways in the piston at room temp. It is a press fit in the rod end. Quote Link to comment
Sealik Posted October 25, 2011 Author Report Share Posted October 25, 2011 Your piston is larger than the bore. A 0.4mm is 0.015"/2 = 0.0075" clearance all the way around the piston to the wall. Supposed to be 0.001" to 0.0018" by the FSM for '84 720. At the moment that's almost 4 times past the maximum clearance. What does the bore look like?? Top ring gap is 0.0098 to 0.0157 so your 0.012 is in the middle. The pin should be able to slide sideways in the piston at room temp. It is a press fit in the rod end. There's the problem right there!.... :lol: Typo error... :D I'll snap a pic of that bore Quote Link to comment
Sealik Posted October 25, 2011 Author Report Share Posted October 25, 2011 The bore has vertical marks/scratches Wondering why they didn't press the pin,.... so it was centered...? So...I'll assume they bored the cylinders to fit the rings...not the pistons I'll get a local mechanic to come down and pull another piston, measure the clearances. Quote Link to comment
Sealik Posted October 26, 2011 Author Report Share Posted October 26, 2011 One can make the assumption that the oversized bore relative to piston size contributed to the wear on the rod bearings and pistons...? Need to confirm before I lay into the machinist.... :D The Z24 pistons are from NPR, checked their website.....and most of the piston to cylinder (total) clearances are .04mm...(?) Like 10 times less what I measured. http://www.google.ca/url?sa=t&rct=j&q=npr%20piston%20to%20bore%20clearance&source=web&cd=7&sqi=2&ved=0CFYQFjAG&url=http%3A%2F%2Fwww.gjparts.com%2Fproducts%2Fpistons%26rings%2FNPR2008Book_catalog.pdf&ei=3i2nTo_SCIvdiAK9oKzhDQ&usg=AFQjCNEcHmB0SIkYgsOrqdzWXW0bGwF3dg&sig2=m-MrfZfJH_iz9vYtW_9EPw&cad=rja Didn't know the PN number for my pistons...so I'm 'assuming'. Think I'll upgrade to the KA pistons Quote Link to comment
Farmer Joe Posted October 26, 2011 Report Share Posted October 26, 2011 why does the piston have such bad carbon buildup on the top edge? doesnt this have limited miles? Quote Link to comment
Sealik Posted October 26, 2011 Author Report Share Posted October 26, 2011 why does the piston have such bad carbon buildup on the top edge? doesnt this have limited miles? About 4-5000 KMs I believe http://youtu.be/1JR1onIaxRA Overbored cylinder created blowby....gases then sucked in through the PCV valve...resulting in carbon buildup and other issues. Just a theory.. :) Also noticed the upper half of the rod bearing is worn at the backside....whereas the lower half of the bearing is worn at the front, confirming the piston/rod moving back (pivoting) and forth in cylinder.(?) Initial compression test before I fired it up was 112-125 Quote Link to comment
Sealik Posted October 26, 2011 Author Report Share Posted October 26, 2011 Wondering why they didn't press the pin,.... so it was centered...? ...."The wrist pins on many pistons are offset slightly so as to load the piston slightly to one side. This reduces piston noise as the piston approaches top dead center (TDC) on its compression stroke, then passes over TDC and starts down on its power stroke. "... Checked some other pistons I have lying around..pins are offset also Quote Link to comment
Sealik Posted November 2, 2011 Author Report Share Posted November 2, 2011 Block is at the machinists...rebuild the rebuild Anywho.......A 'breath of fresh air' arrived today....Need some 45s........... Quote Link to comment
datzenmike Posted November 2, 2011 Report Share Posted November 2, 2011 ...."The wrist pins on many pistons are offset slightly so as to load the piston slightly to one side. This reduces piston noise as the piston approaches top dead center (TDC) on its compression stroke, then passes over TDC and starts down on its power stroke. "... Checked some other pistons I have lying around..pins are offset also Doug the pin is offset is to the spark plug side of the piston and not toward the rad or flywheel along the pin length. It's only a mm or less and this is why pistons have a notch that goes to the front to place them properly. Quote Link to comment
Sealik Posted December 27, 2011 Author Report Share Posted December 27, 2011 Sooooooo....update Bought some 46mm 240 SUs on a Lynx manifold...was thinking of using it for the LZ23...but...the intake runners are a lot smaller than the NOS intake posted above. Take quite a bit of grinding...and won't be able to 'aug' very deeply into the IM/runners. Difference between the 2 Found some purple heart wood for the 38-46 insulators....forgot how hard that shit is The aluminum was easier to grind... Test fit...looking through....perfect Now just finish the heat shieldNo doubt have to find different needles for the SUs....they are fitted with RAs.Seems they are just about the richest you can run.Not sure where I got this info but....the common needles for the (stock?) 240 are...from lean to rich...MC, KW, RB, and RA.Soooo...I need to find some fatter needles...any info on the aforementioned is much conducive Quote Link to comment
datzenmike Posted December 27, 2011 Report Share Posted December 27, 2011 SUS SO SEXY Quote Link to comment
Sealik Posted December 27, 2011 Author Report Share Posted December 27, 2011 SUS SO SEXY Yeah......I'm converted... :cool: In theory, should be a lot better than my 38/38....as long as they're jetted correctly. Might be selling some Weber carbs...oh wait....moar projects!.... :D :D :D Quote Link to comment
Z chopper Posted December 31, 2011 Report Share Posted December 31, 2011 nothing sexier than SUs Quote Link to comment
Sealik Posted January 2, 2012 Author Report Share Posted January 2, 2012 Linkage welded and installed with Hitachi trunnion....trunnion is loose till I make a (another ) heat shield. Then I can configure the throttle cable/linkage, which will be mounted to the shield.Figured I should find some cables to remedy the "summer SUs only" issue. Grabbed some dual throttle cables from a snowmobile....ground the ends off to slip into the SU choke fittings.Tightened the set screws.....cycled the chokes with the 1 cable.....perfect The dual throttle cables are converted to 1 (cable) about 12 inched from SUs, that plastic/rubber fitting can be taken apart to access all 3 cables.I guessing I only have about 18 inches sticking inside the cab...past the firewall.So......if it's not long enough and or to remedy a lack of knob or lever to operate the chokes, I'll just find a cabled choke ('kit') and replace that 1 cable Quote Link to comment
datzenmike Posted January 2, 2012 Report Share Posted January 2, 2012 Doug you mentioned the screw with the spring ? Mine just has a bolt in it... ...just down from it is a blue capped fitting (wired on) and below that a PCV valve. Where do you get vacuum advance from???? Have to say those choke cables are making me wet. I guess flattop 38s and round top 45s? have the same choke operation? May have to pick your brains on the how to in the future. . Quote Link to comment
Sealik Posted January 2, 2012 Author Report Share Posted January 2, 2012 Doug you mentioned the screw with the spring Mine just has a bolt in it... Have to say those choke cables are making me wet. I guess flattop 38s and round top 45s? have the same choke operation? May have to pick your brains on the how to in the future. Yeah...didn't have a proper sized fitting....so I'll just use the screw and spring for now. Not sure about the choke cable operation between the 2...unless I had a good pic for comparison. Impressed with those cables.... :D ....just have to secure those nuts so they don't migrate and change the 'cycling' length Quote Link to comment
Sealik Posted January 3, 2012 Author Report Share Posted January 3, 2012 Where do you get vacuum advance from???? Good question...I'm assuming this black capped fitting.I'm basing my 'assumption' on the availability of...well.... no other connections/ports... ... Quote Link to comment
datzenmike Posted January 3, 2012 Report Share Posted January 3, 2012 Damn I need to know also. Quote Link to comment
Sealik Posted January 3, 2012 Author Report Share Posted January 3, 2012 Damn I need to know also. Capped in red.... Looks like choke cables would be clamped in like my other 46s....that should work. My cables actually ran some Mikunis...on a sled that is :D Quote Link to comment
datzenmike Posted January 3, 2012 Report Share Posted January 3, 2012 The vaccum advance port on the SU carburetor gets it's signal from an area just upstream (atmosphere side) of the throttle plate. At idle, when manifold vacuum is high and the throttle plate is closed, the vaccum advance port receives no signal and so the distributor sees no advance from it. Crack the throttle open a bit like when you begin to accelerate (part throttle) and the vacuum port sees lots of manifold vacuum and gives you a bunch of advance at the distributor. This is also true while cruising down the freeway at part throttle. Not only do you have your mechanical advance in (30-38 degrees total or so) but the vacuum advance will give you another 10 degrees or so on top of that (40-48 degrees or so) which helps extract the maximum amount of energy out of partially filled cylinders due to part throttle running. Now stomp on the gas and manifold vacuum drops to a very low level. Vacuum advance drops off to keep the motor from pinging since the cylinders are now being filled fully, or somewhere near that. A motor would detonate in a heartbeat if there was 48 degrees advance and you were at full throttle. Here the motor only sees the mechanical advance which shouldn't be too much to cause pinging if it's set correctly. Now if the vacuum advance was attached to the manifold instead of the carb, the distributor will see full vacuum advance at idle since there is no throttle plate to seal it off when the throttle is closed. Probably won't cause detonation at full throttle since the manifold and the carb vaccum port will see essentially the same signal at that point. Most likely you will see a much higher idle with the advance hooked to the manifold since you are getting 10 degrees or so more advance at idle versus hooking it tho the carb port. Some cars take their vacuum advance from the manifold but if you are running SU's, it's best to use the carb port. Quote Link to comment
Sealik Posted January 4, 2012 Author Report Share Posted January 4, 2012 The vaccum advance port on the SU carburetor gets it's signal from an area just upstream (atmosphere side) of the throttle plate. At idle, when manifold vacuum is high and the throttle plate is closed, the vaccum advance port receives no signal and so the distributor sees no advance from it. Crack the throttle open a bit like when you begin to accelerate (part throttle) and the vacuum port sees lots of manifold vacuum and gives you a bunch of advance at the distributor. This is also true while cruising down the freeway at part throttle. Not only do you have your mechanical advance in (30-38 degrees total or so) but the vacuum advance will give you another 10 degrees or so on top of that (40-48 degrees or so) which helps extract the maximum amount of energy out of partially filled cylinders due to part throttle running. Now stomp on the gas and manifold vacuum drops to a very low level. Vacuum advance drops off to keep the motor from pinging since the cylinders are now being filled fully, or somewhere near that. A motor would detonate in a heartbeat if there was 48 degrees advance and you were at full throttle. Here the motor only sees the mechanical advance which shouldn't be too much to cause pinging if it's set correctly.Now if the vacuum advance was attached to the manifold instead of the carb, the distributor will see full vacuum advance at idle since there is no throttle plate to seal it off when the throttle is closed. Probably won't cause detonation at full throttle since the manifold and the carb vaccum port will see essentially the same signal at that point. Most likely you will see a much higher idle with the advance hooked to the manifold since you are getting 10 degrees or so more advance at idle versus hooking it tho the carb port. Some cars take their vacuum advance from the manifold but if you are running SU's, it's best to use the carb port. Thanks....another SU bookmark... Soooooo...needed some metal for a heat shield.I knew this traffic sign had a purpose....(a hoarding thing.. )...just didn't know for what until now. Cut it to 'size' and drilled some holes.Bolted the heat shield to the IM with the new gaskets and insulators, then ground the inside all smooth again. Most likely have to notch for dizzy(?) and the hose from the block, for the PCV valveDrill a couple of holes for the return springs etc..Also drilled two 3/8 inch holes in the head for IM coolant flowProbably paint the shield a high heat black Quote Link to comment
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