after rebuilding my engine and sourcing my parts from a vintage racer/old honda motors dealers son. i was enticed to buy the 350 big bore kit. it would operate with great power but after getting kinda of hot from running somewhat hard. it would start to resist and eventually die. I opened the fuel lines to counteract this and the engine seized. i was going about 90 mph when this happened and i didnt think to press the clutch because my focus was staying vertical albeit sliding. the engine unseized at about 55. when i opened the can up. (months later) this is what i found.. .
question1: what was causing that feeling of ressistance/ stalling? piston expansion?
question 2: from the pictures you can see the piston has a big hole in the center. if i change this and clean out the surrounding, will we be in good shape?
question3: is there something else i can do to fix this issue of its unrealiability wthout changing the sleaves and piston size? in other words can the 350 be realiable or should i scale back to the original now that the can is open.
btw, the engine runs real rich, but anything less in the mixture and it wont run at all.
350 big bore blow out
350 big bore blow out
Ricky
Nasty! Q1 - Overheating ( caused by bad timing, wrong plugs, wrong mixture etc), means lower performance from the oil which means more heat etc. etc. Essentially part in the engine are working beyond their max operating temperature. What did the other piston / head look like Q2 - Unlikely if you think about it. Will you have corrected any of the above? Q3 - Ride slower. Get some help in setting the bike up properly. Think about mixture, timing, lubrication, piston, cylinder, ring clearances. Don't forget that most of that molten aluminum is now in your crankcase and lubrication system. I would strip the whole motor and clean it up. Good luck G '60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F I would say that you probably had a engine that was too advanced and too lean. When you said it runs rich and will not run at all with anything less. That's not rich. That's lean.
The engine losing power was it was seizing from high combustion temps. That could be due to too tight a piston to cylinder clearance or flogging it too hard. But I really suspect it is at least partially if not fully tied to your holed piston cause. And IHMO, you will not hole a piston from flogging your engine. It may seize or partially seize, but will not hole a piston. What makes you think it is too rich? Does... sorry, did black smoke come out of the exhaust. Would the plugs foul and not fire? I would argue that a hole in the middle and spattered aluminum is not a lubrication issue. You cooked that puppy with timing, mixture or both. I would think that your cylinders and head will clean up fine. G-mans point about contamination in the bottom end is well taken. But I know more than one guy who has holed a piston in a Brit bike and just did a top end, oil change, retune, retime and was good to go. Do clean out your oil filter. My condolences. regards, Rob Rob
Sensible thoughts. When I was thinking of lubrication it was more along the lines of the tightening up Ricky described. I agree, the hole is due to timing and or weak mixture. I wouldn't rule out other issues with that motor, though. Those Brit bikes that had holed pistons didn't generally have lots of fancy roller bearings in their crankcases. G '60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F
ok , 1. the engine was running rich because these was gas in both exhausts. the screws were turned 3.5 times by the way on the other (richer side) the one that popped was 2.5 turns. those carbs were never tuned the same though, it just didnt work that way, not suure thats the normal thing or not though. i know the tunining standards though caled for .5 to 1.5 turns only (max) . probably has to do with the increased displacement. the jet were set in the middle (default) .
2. ok so yes, the engine must have been over heating. the run i did just before this one, the first for top speed, the engine started to smoke alot after the run (burning oil) . for future referemce, is this an indication of overheating? 3. plugs i was running are NGK D8HA 4. timing, i will redo this but does bad timing have any sound indicators? i had a pro do the timing for me so i figured that was the least of the problems. 5. is there any way i can inspect for pinging now with the can open. should there be marks? because the bike would make a pinging type sound around the cam but i heard that was normal and not pinging by the mechanic. could tha have contributed cause? 6. about the molten aluminum. i have cleaned it out of the globe, it looks like some is in the exhaust port (more than the other side) ill assume because of the vacuum effect of the engine. does that need to be cleaned out? (looks like some on the valve stem) also i would hate to rebuild more than the top end. i have a magnetic plug on the bike. should that be good enough. (cleaning in frequent intervals) 7. what oil filter should i clean, the one at the pump? or the one on the side. that one is a pain the ass to take apart by the way. any suggestions on how to open that one would be appreciated, but first is it necessary.? btw, this hurts, i had about 500 miles on this rebuilt engine. 8 . one more, sorry,.. i had put in a new clutch basket. after about 400 miles, if you tried to feather into second gear the bike would not catch it right off, but kind off neutral out then suddenly pop into 2nd real brash seems like something would eventually break; the only way to get it in confidently was to pop it in a higher than mid rpms. any explanations for this? this may lead to taking the whole dam thing apart. i put too much work into this bike for this, heres what she looked like before the black friday. also what i originaally bought her as (crazy)
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