Hi Guys,
Been futzing with the BlackHawk to try and get it where I want it (the neverendingstory), and in the process of trying to ID why the bike has been misbehaving on the right cylinder (spark and fuel are fine) figured out that the compression is way low. (BTW, finding a compression gauge that will fit those threads was a impossible task, finally welded up a fitting using a M12 fine thread bolt with a hole drilled in the middle)
I'm not sure what is responsible, I'm assuming the rings, but I'll need to check the valves and stem seals as well I suppose. Any advice as to identifying the culprit? I will be putting some oil in the cylinders to see if that influences the compression, I don't have any leak down equipment. The cylinder is really low around 50psi, so I'm hoping it's obvious.
Anyway, I've been thinking about getting the engine beefed up for awhile, so this looks like the opportune time. I've been thinking of sending the cylinder to Bore-tech to get the 350cc kit installed. My question is: what else should/can I do to go with this update to make a nice street bike with a bit more cahones? I currently have a Sachse ignition and Amal carbs on the thing, and in spite of the low compression, the bike has actually been running pretty well, albeit with increasing weakness and stumbling here of late. I have aftermarket free-er flowing pea shooter mufflers and UNI pods on it as well. Will I need to recarb it with the big bore, or will rejetting be enough? I assume I have plenty of options with the Sachse ignition. What about a new cam? Megacycle has an upgraded street cam that sounds like it would work. Any experience, comments, suggestions, pitfalls or other catcalls are welcome!
Thanks for your help!
Jack
Time for a Motor Update
Compression tester?Jack
You should find a real compression tester before you get too carried away with yanking that motor. How big is the hole you drilled in the bolt? If it restricts the flow of compressed gas into your compression gauge it will read low. Is your weld airtight? If not, your compression gauge will read low. You may want to spend some time searching this site to see what others have found when they had either weak performance or stumbling. You could have low compression but, if it is not what is causing your complaints, a big bore kit won't give you the relief you are after. My $0.02
Re: Time for a Motor UpdateI once made a part which would thread into the head to check the compression.
I found that I needed to add a stopper so the air from the hole went to the gauge but needed to stay in the line. I added a Schroeder Valve in the line to KEEP The Pressure at the gauge. A connecter from the gauge to the end with the threaded part will have a valve in the end part. ............lm
Thanks for the suggestions folks. I welded the M12 fine threaded rod onto a fitting that came from a compression testing kit that did not have the right size fitting. It screws into another fitting on the tester that has a one way valve on it. I actually brazed the rod and fitting together and the hole I put in it was roughly the same diameter of the other fittings included in the kit. I'm not positive how airtight it is, but me blowing on the one side of it with my finger on the other doesn't seem to leak...! We do have a Harbor Freight, as a matter of fact I bought a kit there a while back, but the one I got did not have a compatible fitting either so after buying 2 kits, I gave up and tried to make my own.
Anyway, the left cylinder pressure is a little over 100psi, still low, but the right will barely get to 50 after many cycles. So, since I'm using the same tester (leaking or not) on both sides, it sure looks like the right is low. I just dropped the motor and popped it open (first time open for me with this engine), the right piston and combustion chamber is a lot blacker, wet with significant carbon buildup, the left is flat black with tan on the valves - something unhappy is going on with the right cylinder. Nothing obvious as far as the rings and cylinder bore on the right. I've been wanting to try increasing the ccs of the engine, so I am in a way using this as an excuse to increase the bore. My other concern is that I have something up with the valves on the right side that I might be missing. While they are black and wet, the seats look as good as I can tell. I don't know if there's a way to examine these things satisfactorily with the engine disassembled. So, if anyone has experience with going bigger on the engine size, any advice would be welcome as well. I'm not looking to build a race engine, I'd just like to end up with something reliable but with some more grunt. Thanks folks, Jack
I know you PM'd me about the big-bore kit, but I thought of one more thing, so I may as well post it here.
Having done the 358 kit, I can't really say that it added much in the way of 'grunt' on its own. The thing that I found that really changed things for my bike was the combination of it and the NOVA 5-speed transmission. But then you're into something entirely different, and I don't know if you want to go down that road.
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