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Post by scooterpimp on Dec 12, 2014 5:49:54 GMT -5
Is it me , or are there more problems with these supposed big bore heads???than thier worth , seems all that reused stock head had no issues .
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Post by blaq on Dec 12, 2014 10:13:41 GMT -5
Is it me , or are there more problems with these supposed big bore heads???than thier worth , seems all that reused stock head had no issues . What the stock head you speak of post a pic or something
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on Dec 12, 2014 13:13:44 GMT -5
First my apologies to the OP but this thread is the perfect place to share this information. These photos in this reply will not stay up forever, so if you want copies, just save them to your pc. ScooterPimp, you are right. there are lots of problems with not only the big bore heads, but even the kits (cylinder & piston). So that everyone can be on the same page so to speak, some background. In Nov I purchased two BBK from two different suppliers and a used "ported cylinder head". One 72cc BBK (no head)was from Valley Scooters and the used head was from a user on this forum, that bought it as an engine asm from Scooters to Go. The other 83cc BBK with head was purchased off CL. I wanted to see the porting type and quality of the used head, the 72cc BBK was used in an upgrade where the 63cc OE engine convex domed piston had a damaged dome to the first compression ring. The 83cc BBK with head was purchased to upgrade another scooter. Here are the pictures pre-tear down of the Scooters To Go ported head: Used Head:Cam Journal Damage:Rocker Asm Journal Damage:Stepped Volume Porting:Exhaust Volume Porting:Oil & Carbon Deposits:As you can clearly see the porting was done in a stepped fashion and out to the gasket opening size in a volume porting type. Also the cam journals in the head are galled, and the P.A.I.R. port was not open. Also worthy of note is the excessive amount of oil & carbon buildup in the short time this engine ran. The porting is very amateurish but does have one saving grace and that is that they did not attempt to polish it. The cylinder head gasket was of the correct thickness, and both the previous head owner and the purchaser of the cam both stated there was no bearing problems on the cam. The excessive carbon and oil build up tells that the engine was getting too much fuel and the piston rings never seated properly. The Valley Scooters 72CC BBK, came with a concave domed piston, and a 1mm too thick head gasket. These two changes imply that the manufacturer was reducing the compression in the engine to CYA. Also the lower chain guide porting was too tight and was restricting the installation and movement of the guide. Metal was removed to overcome this flaw. I wanted to see if this head gasket was for any other reason such as cylinder height. As you can see, when the 1mm too thick gasket is used it does two things; it stretches the timing chain and causes stress in the rocker asm. Thus if it is used, either the chain will fail or the rocker asm will fail resulting in catastrophic engine damage. Here are photos of the gasket and the engine with that gasket and finger tightened head nuts on the engine. You can clearly see the stress on the rocker asm, if it were torqued. Too Thick Head Gasket:Engine Stresses From Head Gasket:BBK from CL seller: The piston was concave domed, had the correct head gasket, and the head just had bigger valves without any porting. What does all this mean? increased cylinder size = needs more fuel concave piston = reduced compression and power and needs more fuel volume ported head, even done correctly = needs more fuel bigger valved head = needs more fuel Remember that volume porting is not a one way door, the charge goes both ways so this requires more fuel as well. There is a point where what is required is a bigger carb with finer adjustments to overcome some of these problems. Also it might be advisable to swirl the A/F charge to dry it out more for better overall combustion. Keep in mind, that an engine where the piston rings don't seat properly or completely is destined for premature failure.
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tvnacman
Scoot Enthusiast
Posts: 408
Location: NYC
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Post by tvnacman on Dec 12, 2014 17:00:25 GMT -5
First my apologies to the OP but this thread is the perfect place to share this information. These photos in this reply will not stay up forever, so if you want copies, just save them to your pc. ScooterPimp, you are right. there are lots of problems with not only the big bore heads, but even the kits (cylinder & piston). So that everyone can be on the same page so to speak, some background. In Nov I purchased two BBK from two different suppliers and a used "ported cylinder head". One 72cc BBK (no head)was from Valley Scooters and the used head was from a user on this forum, that bought it as an engine asm from Scooters to Go. The other 83cc BBK with head was purchased off CL. I wanted to see the porting type and quality of the used head, the 72cc BBK was used in an upgrade where the 63cc OE engine convex domed piston had a damaged dome to the first compression ring. The 83cc BBK with head was purchased to upgrade another scooter. Here are the pictures pre-tear down of the Scooters To Go ported head: Used Head:Cam Journal Damage:Rocker Asm Journal Damage:Stepped Volume Porting:Exhaust Volume Porting:Oil & Carbon Deposits:As you can clearly see the porting was done in a stepped fashion and out to the gasket opening size in a volume porting type. Also the cam journals in the head are galled, and the P.A.I.R. port was not open. Also worthy of note is the excessive amount of oil & carbon buildup in the short time this engine ran. The porting is very amateurish but does have one saving grace and that is that they did not attempt to polish it. The cylinder head gasket was of the correct thickness, and both the previous head owner and the purchaser of the cam both stated there was no bearing problems on the cam. The excessive carbon and oil build up tells that the engine was getting too much fuel and the piston rings never seated properly. The Valley Scooters 72CC BBK, came with a concave domed piston, and a 1mm too thick head gasket. These two changes imply that the manufacturer was reducing the compression in the engine to CYA. Also the lower chain guide porting was too tight and was restricting the installation and movement of the guide. Metal was removed to overcome this flaw. I wanted to see if this head gasket was for any other reason such as cylinder height. As you can see, when the 1mm too thick gasket is used it does two things; it stretches the timing chain and causes stress in the rocker asm. Thus if it is used, either the chain will fail or the rocker asm will fail resulting in catastrophic engine damage. Here are photos of the gasket and the engine with that gasket and finger tightened head nuts on the engine. You can clearly see the stress on the rocker asm, if it were torqued. Too Thick Head Gasket:Engine Stresses From Head Gasket:BBK from CL seller: The piston was concave domed, had the correct head gasket, and the head just had bigger valves without any porting. What does all this mean? increased cylinder size = needs more fuel concave piston = reduced compression and power and needs more fuel volume ported head, even done correctly = needs more fuel bigger valved head = needs more fuel Remember that volume porting is not a one way door, the charge goes both ways so this requires more fuel as well. There is a point where what is required is a bigger carb with finer adjustments to overcome some of these problems. Also it might be advisable to swirl the A/F charge to dry it out more for better overall combustion. Keep in mind, that an engine where the piston rings don't seat properly or completely is destined for premature failure. Just wanted to add this to the last line of your post www.youtube.com/watch?v=BdQAK96SysEJohn
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Post by scooterpimp on Dec 12, 2014 18:00:41 GMT -5
Is it me , or are there more problems with these supposed big bore heads???than thier worth , seems all that reused stock head had no issues . What the stock head you speak of post a pic or something Stock head assembly that was removed to instal cyl. Kit.
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Post by niz76 on Dec 12, 2014 18:08:16 GMT -5
If this helps anyone out: I purchased and installed the 4t 50mm BBK w/head for $55 from 02starrider on ebay with absolutely no problems....
Kit also came with extra goodies- roller weights, exhaust gasket, oil pump, main jet, etc.
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chris962
Scoot Member
Anyone out there good at diagnosing a no-start when doing a 72cc BBK on a Taotao 50cc scooter?
Posts: 24
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Post by chris962 on Dec 13, 2014 2:32:17 GMT -5
I'm glad you had no troubles with that 50mm BBK niz76, but I've heard that this size BBK is too big for a 50cc scooter and while it works initially, all that extra power is too much for the crankshaft and its bearings and will eventually seize. I got the 72cc, or 47mm, BBK as I've heard that size isn't too much power for a 50cc engine, but man have I had problems with it! I thought it was the timing at first, but did some studying on no-start issues and saw a good video by Matt of Rolling Wrench concerning low compression. He did a test on his scooter and it was reading 90psi whereas a well running 50cc scooter needs compression readings from 120psi to 170psi. His scooter made the same sort of going nowhere cranking sound on the video, but he wrote that he eventually got this scooter to start up, but it must have starting problems all the time. On the other hand, I have not been able to start my scooter so far and have made 4 attempts so far to take apart and put back together the new engine, 1st time with the stock head with 69mm valves, the other times with the new head with 64mm valves 'after' I purchased separately new rocker arms for a head with 64mm valves. I have also 'only' used the original 'stock' head gasket for both heads and that is due to the fact that the 'new' head gasket designed for the new head simply did 'not' fit onto my engine. I believe the problem with the new head gasket is the holes are too small for the upper right, and/or lower left, dowels for the engine studs. I suppose one could cut out a bigger hole on the new head gasket, but my thought on the 1st attempt was that doing so would change the original design of the new head gasket and thus cause a 'leaking' problem with the engine. Anyway, I think I have low compression and think it is due to using the old head gasket as I've read that you can't reuse an old head gasket after you take off the head. A friend said it was okay to re-use the stock head gasket, but even if that is right, it's still true that the stock head gasket was designed to be used with the stock jug and stock head. I haven't gotten around to measuring the stock piston, but my guess when comparing it to the new 47mm piston is that it's a 39mm piston, so that stock jug, the dowels designed for my 50cc engine, and the new head gasket with small holes that won't fit over those dowels, plus the new differently sized 64mm head, are all probably combining to result in much lower compression than it had with the original stock engine, which started right up before the BBK. Btw, I've heard that 02starrider has good parts, was going to get his 50mm BBK, but did not want my scooter to work fine for a few months with lots of increased power, then seize up suddenly with a worthless engine, so I heeded the warning of my friend.
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Post by niz76 on Dec 13, 2014 4:37:48 GMT -5
Ya the cranks are tiny and the 50mm piston is huge= broken crank rod eventually. Call me a gambler haha. So you did a compression test? What's your reading?
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Post by Clank on Dec 13, 2014 4:50:36 GMT -5
First my apologies to the OP but this thread is the perfect place to share this information. These photos in this reply will not stay up forever, so if you want copies, just save them to your pc. ScooterPimp, you are right. there are lots of problems with not only the big bore heads, but even the kits (cylinder & piston). So that everyone can be on the same page so to speak, some background. In Nov I purchased two BBK from two different suppliers and a used "ported cylinder head". One 72cc BBK (no head)was from Valley Scooters and the used head was from a user on this forum, that bought it as an engine asm from Scooters to Go. The other 83cc BBK with head was purchased off CL. I wanted to see the porting type and quality of the used head, the 72cc BBK was used in an upgrade where the 63cc OE engine convex domed piston had a damaged dome to the first compression ring. The 83cc BBK with head was purchased to upgrade another scooter. Here are the pictures pre-tear down of the Scooters To Go ported head: Used Head:Cam Journal Damage:Rocker Asm Journal Damage:Stepped Volume Porting:Exhaust Volume Porting:Oil & Carbon Deposits:As you can clearly see the porting was done in a stepped fashion and out to the gasket opening size in a volume porting type. Also the cam journals in the head are galled, and the P.A.I.R. port was not open. Also worthy of note is the excessive amount of oil & carbon buildup in the short time this engine ran. The porting is very amateurish but does have one saving grace and that is that they did not attempt to polish it. The cylinder head gasket was of the correct thickness, and both the previous head owner and the purchaser of the cam both stated there was no bearing problems on the cam. The excessive carbon and oil build up tells that the engine was getting too much fuel and the piston rings never seated properly. The Valley Scooters 72CC BBK, came with a concave domed piston, and a 1mm too thick head gasket. These two changes imply that the manufacturer was reducing the compression in the engine to CYA. Also the lower chain guide porting was too tight and was restricting the installation and movement of the guide. Metal was removed to overcome this flaw. I wanted to see if this head gasket was for any other reason such as cylinder height. As you can see, when the 1mm too thick gasket is used it does two things; it stretches the timing chain and causes stress in the rocker asm. Thus if it is used, either the chain will fail or the rocker asm will fail resulting in catastrophic engine damage. Here are photos of the gasket and the engine with that gasket and finger tightened head nuts on the engine. You can clearly see the stress on the rocker asm, if it were torqued. Too Thick Head Gasket:Engine Stresses From Head Gasket:BBK from CL seller: The piston was concave domed, had the correct head gasket, and the head just had bigger valves without any porting. What does all this mean? increased cylinder size = needs more fuel concave piston = reduced compression and power and needs more fuel volume ported head, even done correctly = needs more fuel bigger valved head = needs more fuel Remember that volume porting is not a one way door, the charge goes both ways so this requires more fuel as well. There is a point where what is required is a bigger carb with finer adjustments to overcome some of these problems. Also it might be advisable to swirl the A/F charge to dry it out more for better overall combustion. Keep in mind, that an engine where the piston rings don't seat properly or completely is destined for premature failure. yes they will :thumb:
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on Dec 13, 2014 8:38:43 GMT -5
John, I hope that is NOT you in the video showing us how you hone a cylinder. Whoever it is has no idea how to perform that job right. Here would be a great place for you to show us photos of your BBK up close, especially the pistons, cylinder heads and gaskets. You might even consider measuring the piston to cylinder clearance as a demonstration of your product quality. I don't think anyone, including myself, would mind some self promotion to add to this discussion from parts sellers. Chris962, I had a stock 63cc that had an oil leak @ the base gasket where someone had used a lot of rtv silicone trying to stop the leak, after repairing that I wanted to test the theory of annealing the old head gasket, coating it and reusing. After properly sequentially torquing the head nuts & bolts, I ran a cylinder leakage test @ 15psi, and again at @ 175 psi - no leaks. After I put a few hundred miles on it, I'll retest to see if it continues to work without leakage. Two additional things I have noticed that might help others: most scooters have an exhaust leak at the pipe flange to the head. I took the pipe from the 'oil leak' scooter and used a flat file to start shaving it flat (old bodyman practice). I didn't have to remove too much metal to achieve this. I have questioned exhaust leaks effect on fuel needs on these small engines and I did notice the scooter started easier cold ambient temps better than before. The exhaust pipe, 50 & 150 are the same at the exhaust flange.
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tvnacman
Scoot Enthusiast
Posts: 408
Location: NYC
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Post by tvnacman on Dec 13, 2014 10:13:23 GMT -5
Bull that is me in the video . When I rebuilt a few engines and did not do what I did in the video . I got about 700 miles out of the rebuild . When I ran a honing stone inside the the cylinder they seem to go more than 2 years and over 3000 miles . Now bare in mind I'm no machinest , but the rebuild lasts a lot longer when I do what I did in the video . So do you have a link or video for textbook honing . I always look for improvement .
Jojn
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on Dec 13, 2014 16:50:05 GMT -5
I know of no videos that teach how to properly recondition cylinders. The last book I read on the subject was in 1965, and I am sure it is long out of print.
btw.. I meant no dis-respect
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chris962
Scoot Member
Anyone out there good at diagnosing a no-start when doing a 72cc BBK on a Taotao 50cc scooter?
Posts: 24
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Post by chris962 on Dec 13, 2014 18:36:06 GMT -5
Thanks Bull! What did you coat the head gasket with? I just used some motorcycle oil to lubricate it. What did you use to heat up the head gasket? My head gasket looks good, but the only reason I used it was because the new head gasket had smaller holes and didn't fit over the dowels and assumed I needed those two dowels for the entire head to torque down properly during re-assembly. One funny thing is I saw a video recently advising to pull the throttle to WOT six times when a scooter hasn't been started for 2 weeks and mine hasn't started for 2 months now, plus I actually did pull the throttle a few times 'after' the 1st attempt, but was worried I would flood the engine. At that time, I'm glad it didn't start because I didn't realize I had cross-threaded the spark plug yet on the old stock head. I knew there was a problem though when I couldn't put the spark plug cap over the spark plug, but was simply happy to finish the job after 8 long hours of work the 1st time. By the third attempt, I even took off the side panels and finished re-assembly in a little over 3 hours, so not so bad, but didn't have to redo placing the piston rings (took a long time) and even though I found out on the 2nd attempt that I had cross-threaded the spark plug and there were metal shavings in the combustion chamber and on the crown of the piston, I carefully inspected the cylinder below it and it was squeaky clean, so am going to drain the old oil right away before trying to start again, then should I ever FIRE UP that new engine, I'm going to change the oil again to ensure I clean out the entire engine case. Anyway, getting back to what was funny about 'not' trying to pull the throttle six times after the 3rd and 4th re-assemblys of the head is that this technique might have enabled me to start the engine...doh! But, if the engine 'did' turn over after that 1st attempt, that might have been disastrous with those metal shavings in the combustion chamber, so better it didn't turn over! Anyway, I'm not 100% sure that I have low compression, but that could be the present reason for the no-start. I've eliminated fuel, air, and spark as the reasons for the no-start with various checks, but never thought about a possible leak in the new head with the old stock head gasket that might not fit properly with that new head. If my hunch is right, then there would be a possible slight air leak causing low compression,...then again the simple reason for the no-start might be I just needed to add more gas initially due to sitting for so long! Anyway, that possible reason is sort of funny because it's something so elemental. There are literally hundreds of things that can go wrong when doing a BBK, but not pulling the throttle 6 times? Simple.
@ niz76, I didn't do a compression test because I cannot afford to get a compression tester at Harbor Freight this month, but want this new engine FIRED UP, and am 'not' walking my scoot an hour to O'Reillys parts to borrow one! I've eliminated fuel, air, and spark as the possible causes of the no-start via several checks suggested by a friend, then saw a video by Matt of Rolling Wrench showing a compression test with a reading of 90psi and during the video it cranked many times, but wasn't anywhere near turning over, so my 'guess' is I've got low compression, especially since I used the old stock head gasket designed for the original head with 69mm valves and the new head has 64mm valves and that new head gasket had holes that wouldn't fit over the two dowels, so clearly that BBK is designed for a different engine. Bull above said he somehow heated up his old gasket and got it to work on his scooter, so asked him how he did it, but will take time for him to answer. His old base gasket was leaking oil as you can see above, but he said the annealing worked and he had no oil leaks and good psi readings. Anyway, I don't really care about compression tests because all the testing in the world is 'not' going to get my new engine to FIRE UP! I got smoke once by using John's idea of taking off the carb and intake manifold and dribbling some gas directly down the intake hole into the engine, so given that it 'smokes', then I'm near to getting some 'FIRE', and once I get the latter the problem will be solved. My scooter had been running 'great' before this BBK and only needed an oil change as the oil was getting old, but those metal shavings I found when doing the second attempt after having to buy a new set of rocker arms so I could use the new head,...well, that got me a bit nervous. Anyway, I'm sure the no-start is something very simple, the 1st time it would be the metal shavings and 'glad' it didn't start that time, but after I cleaned it up and installed the new head with smaller valves and new rocker arms, I just think it's something very simple, like 'not' pulling the throttle six times! The damn thing is temperamental at times! But, I saw guys starting a very old motorcycle, and even a moped built in 1915,...one of them hadn't been started for 26 years!,...so after 2 months of not starting, I think it's something very simple and the no-start as simple as 'not' pulling the throttle six times. Sometimes there's a tendency with mechanics to overthink things when all that is necessary is cranking the damn thing over and over and over again, plus pulling on the throttle six times, then voila,...FIRES RIGHT UP! I never even thought of this possibility as there are many possibilities for little mistakes when doing a BBK, but my mind changed after watching several of these videos with very old mopeds and old motorcycles being very hard to get started, which with my scoot sitting for 2 months, the situation could be the same, and once my scoot fires up once, it will be back to normal and fire up immediately on the first push of the start button and no need to pull on the throttle at all. Simple.
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tvnacman
Scoot Enthusiast
Posts: 408
Location: NYC
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Post by tvnacman on Dec 13, 2014 20:36:32 GMT -5
I know of no videos that teach how to properly recondition cylinders. The last book I read on the subject was in 1965, and I am sure it is long out of print. btw.. I meant no dis-respect I did not see any dis respect from your post , that was a brand new jug with a smooth sleeve . Perhaps there is a better way to hone a cylinder , I'm willing to learn, at the moment that yields the best and longest positive results . I know there are guys here that the answer is second nature too them . For the record I wasn't born yet when you read the book . If you should come across something to shed some light on the subject please share it . John
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Post by niz76 on Dec 13, 2014 21:07:53 GMT -5
I have also annealed copper head gaskets and used them over and over successfully. Annealing is a fancy name for a very simple process- simply heat the head gasket to red hot with a torch by moving the torch around. This will make a copper head gasket nice and soft again and ready for re-use.
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