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Post by scootlife on May 30, 2015 16:34:20 GMT -5
I just installed a HOCA 52mm BBK, HOCA Big Valve head, I have a 44mm stroker crank, A9 cam and other upgrades. My scoot ran perfect with the 100cc bbk I previously had in it. Now it turns over, but only gets 60psi compression and no combustion. ANyone have any ideas?
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Post by niz76 on May 30, 2015 16:51:27 GMT -5
Assuming all is well with the compression tester, 60 psi is too low for the scoot to even start. 100-110 is minimum for it to even fire. Something like 150 psi would be great!
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Post by usmcdoc on May 30, 2015 17:03:15 GMT -5
I just installed a HOCA 52mm BBK, HOCA Big Valve head, I have a 44mm stroker crank, A9 cam and other upgrades. My scoot ran perfect with the 100cc bbk I previously had in it. Now it turns over, but only gets 60psi compression and no combustion. ANyone have any ideas? Put a few drops of oil down the spark plug hole...then test compression. If it goes up..your rings or piston and rings are shot. If not..then most likely(and I see it often on the 50+mm kits) It indicates your connecting rod bearings (lower end of rod on crank) It indicates they are so far worn..or gone completely...therefore your piston cannot travel all the way to TDC..and in such a case you will not be compressing the fuel/air mixture enough to raise compression and produce combustion. Another possibility could be a blown or leaky head gasket. Glenn
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Post by scootlife on May 30, 2015 18:51:13 GMT -5
Brand new piston and rings, new gaskets, no play in connecting rod.....maybe I am not at top dead center? I have a A9 cam which has an "A9" on one side and a hole 180 degrees from the A9. I am not sure which should be at the top when I'm installing the cam. Any ideas?
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Post by scooterpimp on May 30, 2015 18:59:51 GMT -5
Timing off? Valve stuck open? Rings staggered? Can get general idea lining lobes of cams side by side to see which is the mark to align by. Tossin some ideas out there.e
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Post by scootlife on May 30, 2015 19:09:15 GMT -5
rings are staggered....
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Post by usmcdoc on May 30, 2015 20:01:26 GMT -5
Brand new piston and rings, new gaskets, no play in connecting rod.....maybe I am not at top dead center? I have a A9 cam which has an "A9" on one side and a hole 180 degrees from the A9. I am not sure which should be at the top when I'm installing the cam. Any ideas? Did pressure go up when you put a few drops of oil down the plug hole? Answer is...you didn't do that as suggested. Not being a smart ass..but anything mechanical is a 'step by step' process. Not just jumping around to different things and guessing. Ok..so the piston and rings are new..and it was running well. Then something happened. New piston rings or not..if for instance the oil pump failed..guess what? Those are no longer 'new' parts now are they?. You say "Maybe I am not at TDC?".. Ok why would you ask that? If it was before and ran..you should still be reaching TDC right? Cam goes big hole up and 2 small holes parallel with the deck of the head. Here is the deal.. I have small parts/repair business. You say this part can't be the problem. That is THE biggest pitfall for anyone in the electronics or mechanical field. Yah see.. EVERY part could be part of the problem..UNTIL you test to rule them out. That is why for EVERY problem these scoots have.. I have a 1,2,3,4,5 step by step process I follow to rule out problems. Ask the very proficient scoot mechanics on here..they have the same. You cannot go..1,5,3,4, ah skip the step 2 that can't be it. You say you feel no play in the con rod..ok was that test vertically or latterly done? Worn bearings cannot always be 'felt' by human touch either..as a few 1,000th can cause an issue. Also again..MANY here will tell ya..new parts don't mean sh*t. We have ALL had new parts that were defective..and the most common ones are CDI's,Voltage Regulators and stators. Cylinder components as well..hell I once got a BBK where the ring gap was so huge..it looked like they used a Nickel to measure the gap..lol.. No joke either. Lastly..one of the biggest 'boo boo's' folks do when they have an electrical or engine problem..is tear that system apart. Whether electrical or mechanical..ya damn better diagnose the system while it is complete and intact..BEFORE you disassemble any of it. So start from the beginning if you will..and go step by step as instructed by folks here and you will be back on the road in short time. k? Glenn
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Post by katastroff on May 30, 2015 20:28:09 GMT -5
Like Doc said, if you dig for a treasure, you dont start 20 feet deep. Problems are the same, dig into it till you find what wrong. I've seen many up here where i live who posted on FB about simple problems and got for answer: "your crankshaft is ruined" while the problem was something simple and dumb like a badly installed airbox. 1 step at the time, and start with the simple stuff like, tightening up those head bolts. You'll get to the root of it at some point, just dont split open your crankcase if its only out of gas.
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Post by Fox on May 30, 2015 21:45:47 GMT -5
Could someone clarify for me since I never have gotten into BBK's and modding a whole lot.
If you put a stroker crank on the engine don't you have to raise the cylinder off the engine some with extra gaskets or whatever so the piston doesn't hit the valves?
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Post by scooterpimp on May 30, 2015 22:37:37 GMT -5
Sometimes yes & sometimes no on cly lifting , some cyls are ok with stroked crank.hope he didnt wack a valve?or over lift the cyl?
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Post by usmcdoc on May 31, 2015 4:51:16 GMT -5
Sometimes yes & sometimes no on cly lifting , some cyls are ok with stroked crank.hope he didnt wack a valve?or over lift the cyl? Good point! I didn't even mention that because I figured if he had the skills to drop the engine and split the cases to drop in the stroker crank..he would have the knowledge and skills to know that a longer stroke = well a longer stroke. Stroker cranks do have their advantages and I love them. While they don't offer higher top end per se..the extra torque they do provide can be upgeared to do so. If anyone here is as old as me..they will remember the 'Street Class' Drag races..where they would take a Chevy 350..bore and stroke it to a 383 for more power. The 500 Cadillac engine could be bored and stroked to right about 700 cubic inches! Drop either of those into your '72 Nova and ya really had something then!
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Post by scootlife on May 31, 2015 6:35:29 GMT -5
Doc, No need to put down members here in the forum. "if he had the skills to drop the engine and split the cases to drop in the stroker crank..he would have the knowledge and skills to know that a longer stroke...", "Answer is...you didn't do that as suggested...."
Doc, a lot of your "helpful and knowledgeable" comments seem very condescending and pointed. I appreciate the help, but I literally posted this yesterday, then many gave some suggestions and questions as to what I have or haven't done yet. I haven't had a chance to try and drop a little oil through the spark plug, so your first rant was completely unnecessary. I guess I'll wait for admin to give his suggestions, or maybe another member, let's keep this forum helpful and classy, not condescending and rude. Thank you.
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Post by usmcdoc on May 31, 2015 7:01:19 GMT -5
Was not putting you down. What I said was if you had the skills to install the stroker crank..you would have the knowledge to know if you needed to raise the cylinder. So it was a compliment. I went on a condescending rant? No I was just saying when you diagnose an engine problem you should always go step by step and just just guess or assume things. Worry not Sir, I will not comment on anymore things you post. I was just trying to be helpful. Best wishes on your endeavor and I hope you get it fixed soon. Too many read into things..looking for negativity maybe? Sorry, I am retired Military with 21 years service as a USMC Combat Medic..so dealing with overly sensitive people seems to not be my forte in life. Actually, I am going to delete my account here. Otonaki aya sanechii degagala eshoha <-- In Chippewa we say.."May everyones days be blessed ones"
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Post by iwannascoot on May 31, 2015 7:36:06 GMT -5
Doc,
Please don't leave this forum. You were very helpful when I was getting my first BBK for my first scoot. I think you have a lot to offer to the members here and I would hate to see you go.
Billy
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Post by 90GTVert on May 31, 2015 8:15:23 GMT -5
I don't see any need to delete your account over what appears to be a simple misunderstanding usmcdoc. Do what you feel is best for you though. scootlife I don't think Doc's comments were posted with malice, but that's just my opinion. He doesn't have a history of trying to offend people here that I recall. I can see what both of you are saying to some degree. Adding drops of oil before a compression test is a good idea. It should help you determine if the head or rings are where you need to look. Another thing to think about is, did you check piston ring end gaps during install? If so, what were they? Could be that you have a leaky valve. Unfortunately this happens with new parts at times. If it was tough to turn over at first or you heard an unusual tapping, or even if you didn't notice that, there is a chance that piston to valve contact occurred. IMO with cam swaps and stroker cranks it's a good idea to check piston to valve clearance. It's not really fun putting the engine together with clay on the crown, rotating the engine over, and then disassembling and measuring, but it may allow valve damage to be avoided.
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