Question about cylinder wear

[pearljam724]

I have a non Suzuki bike that is in need of a head gasket and thermostat. In which I plan to replace in the next day or so. On this bike I also presume the cylinders are perhaps in need of being resleeved sometime soon. If cylinders are in bad need of a rebore or being resleeved. If you were to stick your hand on top of a piston crown. Is it possible to feel a slight amount of slop in side to side motion if you were to try wiggling the piston if the cylinders need rebored with only the head being removed? I realize that the proper way to measure this is by ring end gap and measuring down inside the cylinder walls. But, I have no intention of removing the cylinders when I remove the head. If it does need rebored, it's not problematic at this point in time. Because the bike easily starts and runs very well at initial start up. What has brought me to replacing the head gasket. After the bike is ridden approximately 20 miles or more. If I attempt to shut the motor off by ignition, it continues to run. Unless, I hit the kill switch. But, it runs well for the first 20 miles. Once the bike shows signs of difficulty shutting off. It's difficult to restart and it will only get me to where I want to go with petcock in prime position once I can get it to restart. I believe the head gasket is junk. In addition to the petcock perhaps needs rebuilt. But, between the first 20 miles approximately and the first start up of the day. The petcock doesn't create the slightest problem. When it acts up after 20 or more miles. It's as if it's not getting enough gas. The carbs aren't the issue. I've had them off several times in the last few months to clean, jet, etc. Is there a cheap, yet fairly reliable digital caliper that is dependable for minimal usage sold at Lowe's, Home Depot, etc that I can obtain quickly that someone could recommend ? Or any other reliable method for measuring inside the cylinder walls when I have the head off ?

[tz375]

Lots of things to consider there. First off even a new piston has some rock at the top. Pistons are smaller at the top than the bottom to allow for differential expansion. I'd suggest that if the bike runs fine, check for compression and leakdown and unless the leak is significant or compression is very low, leave the barrels and pistons alone.

Next, you mention that it doesn't shut off unless you use the kill switch. That suggests a wiring issue. I'd have to think about what's going on there. Power is being cut to the ignition switch but the engine continues to run sounds like overheated plugs but you say it does dies if the kill/run switch is pressed. If we are talking a 2 stroke with magneto/cdi ignition, it means that the ignition system is still energized and that the alternator is still charging. Check the wiring diagram to see if that's right.

Petcock sounds like an issue with a blocked vent to the tank causing fuel flow to decrease until it gets too hot and runs out of gas. It takes a while for the pressure to equalize and fill the float bowls again.

Conclusion, check compression just because you can and then address the filler cap vent hole and if that's OK, test fuel flow from the petcock. Maybe the internal filters are partially clogged.

[pearljam724]

I'm with you on all of that, Richard. As far as the wiring and shutting the bike off. I ran it for a few months at the beginning of the summer without this problem existing and never touched any wiring since early spring. I feel the head gasket is definitely causing the problem with the ignition not shutting the motor off. Plus, I have extremely poor fuel mileage. Even though it runs fine. Both are indications of a bad head gasket. But, it doesn't over heat. I had a pick up truck that did the same thing when I was younger. Result of a bad head gasket. I assume the previous owner removed the thermostat, but I will be installing one when I take the head off. So, even with a properly sized bore / new pistons / new rings. The pistons would still rock a little under the correct circumstances ? If that's correct, I just don't want to be alarmed when I attempted to check to see exactly how much slop I have without removing the cylinders and measuring them correctly. Yes, 2 stroke with CDI.

[GT750Battleship]

Hi re the fuel problem,I agree if it ain't the tap,or dirt/rust in the tank,try the fuel cap not venting
Cheers,
Roger

[tz375]

In that case do what Roger and I suggested and look at the filler cap first and then the petcock and then test Compression just to put it in the record book

[pearljam724]

I didn't have enough time to address the petcock or remove the filler cap as I forgot my key. But, I did find a thermostat installed. I will test the old one tomorrow. To my surprise, I did find a fair amount of carbon on the crowns and quite a bit plugging up the exhaust ports. Not a huge surprise after all, when the previous owner insisted on a 32:1 mix and using the oil pump combined. That may explain the motor not shutting off with the ignition. The previous owner used sealant to install the head gasket. That may have been a problem too. My petcock has no internal filter. But, I have one freshly installed in line. I'll have to test the diaphragm or see if anything is clogging up the petcock. The interior of the tank does mildly need addressed. But, it never created a problem up until the motor not shutting off. I changed the fuel filter a few times in the last several months and religiously cleaned the carbs. I'll check compression over the winter. Is it safe to mildly wet sand the top of the cylinders with 2k grit to remove any stubborn remaining sealant ? Wanted to see if there was any piston play by trying to wiggle them side to side inside the top of the cylinders. Wouldn't move a hair. I've heard that you can't measure a bore correctly at the top of the hole. That it has to be measured down inside the wall. The piston rings are damn near the top of the hole. Under that circumstance, couldn't I get an approximate measurement ?

[tz375]

32:1 PLUS injection! That's a little rich even for me. Water cooled and more than one piston. Are we talking RZ350/500?

Use a scotchbrite scourer and a sharp new razor blade to shave that goop off. I'd suggest not measuring the piston to bore clearance unless you are prepared to remove the barrels and potentially rebore and new crank seals etc. Don't ask a question that you don't already know the answer to as they say. in this case it's don't ask a question unless you are ready to follow the trail down the rabbit hole.

[pearljam724]

Lol ! That's funny. As I know you're one of those " never too much oil guys." Yeah an RZ. I asked those questions, because I wanted to get a ball park idea what size it was bored last. I believe, if I measure across the top it should give me a very good idea where it was bored last. Which is my only intention. To know if it should be resleeved next. Used cylinders for those bikes sell at stupid prices. A lot more than what it would cost to resleeve. Not to mention fewer bores available from used cylinders. But, people fight over em. Lol !

[pearljam724]

Found the problem with the bike not shutting off. I removed the ignition, disassembled it. There was a ground wire that had pulled loose from it's solder inside the ignition housing. Likely caused from side to side motion of the bars. Combined with new head gasket, cleaning the pistons tops, exhaust ports and power valve. She's running extremely well now consistently for long periods.