GX200 compression

Don't have alot of experience with the gx200 and I am looking for some advice. As you can see there was a head gasket leak. The engine has .015 quench and the head milled down even with the first fin. The head bolts were tight. .010 metal gasket. I ran the engine for two years and maybe 30 hours. Blew all the oil out the dipstick first ride this year.

Is this common when running high compression?
Is this just to much compression?
Do I need to change the gasket every year or two?
I see some on here say to regularly re-torque the head. Think this would this have helped?
Would a different gasket help?
 

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Have you ever seen a head flex up from to much compression? It is a Honda head. If I hadn't indexed the plug with a washer it would have hit the piston. Excessive CHT? I didn't see anything extreme but maybe I will have to take some measurements. I used a fairly low end cam. Maybe the lack of overlap is creating some higher cylinder pressures.
 
Excessive temp could cause it. I've heard of too much compression causing gasket problems but that was only in extreme ratios for methanol on bored out drag bike engines.
 
Two years seems like it's done pretty good .
Lap the head , put a new high quality gasket in and go .
Laping the cylinder is going to be harder . I like too use a new whetstone
The ball like texture could be detenation , any hot spots on the plug ?
 
On a side note, the head gasket thickness is determined by the piston in the hole distance to maintain the .030" piston to head clearance. The combustion chamber size is used to set the compression ratio based on the type and octane of the fuel you are using, all while maintaining the .050" piston to valve clearance. It's a balancing act to keep it all in spec which is why engines are dry fitted together and measured before final assembly.

Box Stock Project 196cc Engine And Torque Specifications

Posted by ARC Racing on 3rd Jan 2019

Type: 4 Stroke OHV single cylinder
Displacement: 196cc (12ci)
Bore and stroke: 68mm x 54mm
Compression ratio: 8.5:1
Oil capacity: 14-16oz full synthetic (racing applications)
Clearances and Dimensions
Piston to cylinder wall: .0035-.0045"
Piston ring end gap: .008-.012"
Crankshaft pin diameter: 1.179-1.180"
Connecting rod: Big end bore 1.1825-1.183", small end bore .709"
Rod to crank clearance: .0025-.003"
Crankshaft end play: .010-.015"
Valve lash: .001-.002"
Piston to cylinder head: .030"
Piston to valves: .050"
Torque Values
Stock OEM connecting rod bolt: 10ft-lb (120in-lb)
Cylinder head bolt: 18ft-lb (216in-lb)
Flywheel nut: 65ft-lb Ultra light: 55ft-lb
Rocker arm lock nut: 7ft-lb (84in-lb)
Sidecover bolt: 17ft-lb (204in-lb)
Exhaust stud nut: 17ft-lb (204in-lb)
 
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A few bucks for a side covet gasket and you could check the connecting rod bering for galling. If it's good, tork it back down but never hurts to look. It was killing me not to say that.
 
Thanks for all the replies. The golf ball texture is something I added for turbulance. I really don't see any of the usual signs of detonation, but as you can see from the exhaust valve and plug she is fairly lean. Although, this is also some what typical for leaded fuel. It seemed to make the most power there.

This engine is out of my youngest kids zr120 race snowmobile, so it probably sees much cooler temps than you guys are used too. It runs a flat slide mikuni on an intake tube that it about 16 inches long and an even longer header. Ran really good. Lots of torque with great throttle response. Often saw my youngest pass my oldest coming out of the corners and packing the skis. My oldest rides a complete custom powered by a 30 horse rotax max.

This is my first and only air cooled hot rod. Maybe the heat cycle loosening got me. I think I wil put it back together and keep an eye on the bolt torque and head temp. I may cc the head just for fun. I know it is quite small. As you can see in the upper right on the picture, they cut a good .010 into the first cooling fin. I suspect that the compression is probably to high for the 4 corner head bolt pattern though. I may have to reduce it. I completely tore it down and the internals looked great. Plus one for VR1 racing oil i guess.

Again thanks for the spec chart and letting me poach some information.
 
Probably going to stick to my plan but I cc the head at a little more than 10 cc. With 1.5 cc for the .015 quench, I would be around 17 to 1 compression.

What head is this gx200 or gx160?
Are the silver Honda gaskets better than the black ones sold by ARC?
 
A cam with more overlap will help some.

I would think you are seeing very high cylinder pressures. Especially with what I assume is cold dry air, even at higher altitudes.
I would try more octane. It will hurt power slightly, but help longevity.

I would also consider more duration on the cam, with the long intake and exhaust tracts. Probably won't cost much torque but allow more top end.

The pressure at low end is likely causing the damage.
 
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Thanks again guys. All sound advice. I guess I am going to have to make some decisions. I will post the cam number. I like the idea of more cam. Just wish I would have made my i ntake diameter larger now.
 
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