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GS450 Low Compression after rebuild

  • Thread starter Thread starter JRHemmen
  • Start date Start date
Okay, I wasn't sure if honing would suffice. How do I go about testing the rings without putting it all back together for a compression test?
 
JRHemmen said:
Heres the exhaust valve from the cylinder putting out 40 PSI. My guess is that my timing was off, because the valves didn't look that bad and I have a brand new head gasket.

John, I'll post a picture of the cylinder walls in a bit, I'm headed out to get the spring compressor now.

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Click to expand...

The valve seat is loaded with carbon. You will never get good compression on this hole until that situation is rectified.

Using power tools to lap the valves is not advised since it will cause a ridge to form in the valve.

Most machine shops will face the valve and kiss the tip for just a few bucks. Money well spent.

One other thing to do is measure the valve seat contact patch width. The OEM spec is something like 1.2mm max, but 1.8mm should be okay for a used bike. If the seat width is wider than this I'd get the seats cut though.
 
Nessism said:
Using power tools to lap the valves is not advised since it will cause a ridge to form in the valve.
Click to expand...

A few seconds with a slow speed drill pulling on the valve with a rubber hose won't ridge anything. Did it last night on an XL500 head, the valves are sealing tightly now.
 
Would the bike theoretically be able to run before I hone the cylinders and replace the rings? I'm wondering if it's something I could put off until I take the engine out again to paint the frame, or if it needs done now.
 
JRHemmen said:
Okay, I wasn't sure if honing would suffice. How do I go about testing the rings without putting it all back together for a compression test?
Click to expand...
You can check ring end gap by putting a ring in the cylinder and measuring the end gap with feeler gauges the spec for end gaps are in the manual. As the rings wear, the end gap widens, so this would give you an idea of the condition of the rings.
 
Sure it will run, they will run with all kinds of wear and damage in there, but it will run better with a different cylinder. They are cheap on Ebay, I paid $50 plus shipping for a GS500 cylinder and pistons for my 450. Ten percent more displacement for $50, I'll take it. Actually I have a nice pair of 450 cylinders and pistons if you want them for the same $50.

I can even hone them for you before I send them since you probably don't have a hone.
 
tkent02 said:
Sure it will run, they will run with all kinds of wear and damage in there, but it will run better with a different cylinder. They are cheap on Ebay, I paid $50 plus shipping for a GS500 cylinder and pistons for my 450. Ten percent more displacement for $50, I'll take it. Actually I have a nice pair of 450 cylinders and pistons if you want them for the same $50.

I can even hone them for you before I send them since you probably don't have a hone.
Click to expand...

Makes sense. If I have the consent of everyone who's been contributing to this thread, I think I'd like to put it back together and see if it runs. I've spent well over $1,000 just on parts so far and still haven't seen it run. I'd like some kind of confirmation before I keep spending money on it. Chances are I'd like to buy your cylinders, so please hold onto them if you don't mind. I'll deglaze mine tonight and check the ring end gap to see if its still anywhere near spec. I can post some more pictures when I get home and get everything put back together in a few hours.
 
JRHemmen said:
Makes sense. If I have the consent of everyone who's been contributing to this thread, I think I'd like to put it back together and see if it runs. I've spent well over $1,000 just on parts so far and still haven't seen it run. I'd like some kind of confirmation before I keep spending money on it. Chances are I'd like to buy your cylinders, so please hold onto them if you don't mind. I'll deglaze mine tonight and check the ring end gap to see if its still anywhere near spec. I can post some more pictures when I get home and get everything put back together in a few hours.
Click to expand...

OK, I will hold them, they are just sitting here. Using your new head gasket and buying another will cost more than buying my cylinders. You can check the wear, but that rust gouging, there's no spec for that. If you can feel it easily then it's beyond any limit.
 
tkent02 said:
OK, I will hold them, they are just sitting here. Using your new head gasket and buying another will cost more than buying my cylinders. You can check the wear, but that rust gouging, there's no spec for that. If you can feel it easily then it's beyond any limit.
Click to expand...

It felt completely smooth when I ran my finger over it, so I'm hoping that its just superficial. There's no telling, I feel like every part that comes off the bike reveals some new damage that the POs caused to it.
 
Well if it's too small to feel with a fingernail it won't hurt anything. The good news is you are learning. A lot.
 
I forgot to mention that if there was water trapped in the crankcase, it should be gone by now. I cycled diesel through there once, and then cycled oil through three times after that. By the end it was pure, clean oil coming out of the pan. No telling what the potential damage looks like though. What I could see of the crank and conrods looked good to me at least.
 
There would usually be rust on the crankshaft, on the part of the circle that is sitting at the bottom of the engine at that time. Should be able to see it go around as you turn the crankshaft.
 
Just did a real light hone of the cylinders, wanted to post a picture to see if it's enough. It looks a little stained, but its completely smooth running my fingernail through it.

This is the "dowel" I was referring to.

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Here's a topdown view of the crank case. Not much to see from this angle, but I didn't see any rust anywhere.

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Also, here's a picture of the reassembled head, where you can kindof see whats been appearing on the paint, though some of that is probably oil from me handling it.

25124471282_e9c56ff49a_c.jpg
 
Miraculously, IT STARTS! The throttle line seems rough now, and I had to have someone hold the gas tank because my fuel line is too long, but it starts! Whenever I gave it throttle, a really loud noise like a whip cracking would soon follow. Could this be a backfire from bad timing? I Know for certain that the cams are timed to each other correctly (1 arrow parallel with head, 18 pins between, etc), but maybe the crank was off by a pin or so. I spun until I saw the R, then past until I had the T lined up with the notch near the top left screw hole. Was that wrong?
 
Check the ignition timing as well as recheck the cam timing. Several thing can sound like a whip, could be the cam chain skipping on the sprocket, could be a backfire through the carburetors. For the cam chain, please confirm you loosened the setscrew on the side of the tensioner and locked the locknut with the screw about a half turn or so out? If not the tension might not be tensioning anything, valves hitting pistons will be the next noise you hear, followed by the sound of a lot of money going away very fast.
The cam timing being "Off by a pin or so" can cause instantaneous engine destruction.
 
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Did you release the cam chain tensioner set screw and allow the plunger to jump out?
 
did you have the air cleaner hooked up when you did your test run? It will run lean until you get the air box all hooked up with a good air filter. first start up after years of sitting will be a little rough and that is to be expected until it get fully warmed up. If you can ride the bike around the block a couple of times I'll bet it smooths out when warmed up.

Follow the advice from the previous posts about Ignition timing, cam timing etc. As for the timing marks remember that the cam turns at 1/2 the crank shaft speed so anytime you are checking cam timing you have to spin the crank shaft two full turns for one turn of the cam. I would turn it a minimum of 4 times or more checking timing and cam chain tensioner.

You have come a long way and learned a lot. I admire your tenacity and thirst for knowledge. Good job!
 
I believe the chain tensioner was attached correctly. I just found a set of piston rings for both cylinders for $52, so I'm going to buy those. When I pull the engine out to work on the frame, I'll put those in. I'd like to ride it around and see how it feels in its current condition (after confirming tensioner and timing), but I don't want to have to buy another head gasket because I drove it for 20 minutes.
 
Attached are two videos of the engine starting, you can hear the cracks in the second and in the first a puff of smoke comes out of an air filter (much harder to see on the compressed Flickr video). Not on video, when I took off the choke, it seemed like the engine was shooting up in RPMs, but I hit the kill switch before it had a chance to. Clicking the pictures will take you to the videos.



 
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Yeah, that's the harmless backfire through the carb. Probably too lean with the choke on. The choke adds both air and fuel, if the fuel passage is blocked it adds only air, making it too lean, and it pops like that. Could be other reasons for it, but I'm just glad it wasn't the cam chain skipping.
 
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