"Popping" noise when starting

[johnd]

The "popping" blown head gasket pictures and instructions. This may be a dumb question considering the GZ250 is what it is. But when you remove the head and the timing chain can you get the engine out of time? I have an old Gaveley Tractor and if you remove and reinstall the magneto you have to be careful as if will be (I think) 180 degrees off and will not fire for love nor money.

Mr. Wdnavion: Is you name somehow related to those wonderful Ryan Navion Airplanes from the late forties?

Thanks,
John D

[Quimrider]

Not a complete answer since I'm no GZ250 engine expert, just my 2cents. Spark timing is off the magnito/alternator, so spark timing wouldn't be affected. I could see where your valve timing would get off if you don't get the cam put back in with the same position it was taken out or if you moved the crank shaft at all.

[Water Warrior 2]

Mark as many parts as possible before and during disassembly. Take pics during all the work. Make notes and read them over and over. OR, just be like me with a box of parts and wondering Why it won't work.

[jsmeltser]

I hate it when I have a box of parts and no idea how to get them back together! I'm not the most mechanically inclined guy around.

[wdnavion]

Yes JohnD, we have a 49 Navion which I can't afford to fly just now but it is a wonderful machine.
As to "getting out of time", it is not a big problem. You remove the plug from the alternator side of the engine case and bump the machine in high gear until the "T" mark on the alternator rotor inside lines up in the center of the plug hole. It should have a dab of gray paint from the factory to make it easier to find. Just make sure that you have the rotor in that position when you re-install the camshaft in the head. Make sure that you have the punch mark with the white paint on the camshaft pointing aft and aligned with the parting surface for the valve cover. You do want to make sure that both valves are closed when you remove the valve cover. The difficult part of the job is that there is just barely enough room to get the valve cover on and off the head since it is so close to the frame tube under the fuel tank. Also, in order to get the chain off the sprocket to remove the head, you have to take the two bolts off and remove the sprocket and then the camshaft. It is fun being careful to not drop the bolts and the keeper retainer from falling down into the crankcase where they might be hard to retrieve even with a magnet. Also use tywraps as in the pictures to keep the chain from falling down into the crankcase. It took me about 5 hours from start to finish including inserting the helicoil. The instructions in the factory manual found on this web site was pretty thorough.

[wdnavion]

I am adding this to help (I hope) reduce some confusion in performing the head gasket replacement procedure...

As I stated in the forum, there is not a lot of room between the top member of the frame and the top of the valve cover. If I were going remove the cylinder head again, I would probably use some thin wire ties or possibly some plastic tape to get the wiring harness up on the side of the frame member to get a little more clearance. I think I stated that you want all the valves to be closed when you remove or install the valve cover. This is because the valve springs will push the valve cover up making it difficult to remove and next to impossible to re-install. So the easy way to know that the valves are closed is to remove the spark plug and put the bike in a higher gear and put your finger over the spark plug hole. Slowly push the bike forward until you feel the air pushing out. When you feel the pressure dropping that means that you are at near top dead center and the valves will all be closed. Then you can remove the valve cover. Once you have removed the cover, it is a good time to establish the timing marks so that you will have confidence that you are getting them right when you put the engine back together. Remove the threaded plug in the top of the left hand engine case. Use a flashlight if necessary, but look straight down into the hole as you rotate the engine forward...again you can slowly push the bike forward in 4th or 5th gear until the T mark with the gray paint (in my 2002 bike anyway) is centered in the hole. At that time, if you view the camshaft sprocket from the right hand side, you should have the scribed and white painted mark at precisely the 9:00 position...

Moving on to removing the head, remember that you have to remove the four bolts which mount the exhaust pipe collars. Once you have done that, you will most likely find that you have to remove the single muffler mount bolt under the muffler at the right rear of the bike. Move the pipes forward enough so that there is some clearance when you are ready to remove the head. Then remove the carburetor. I did not remove the screws attaching the adaptor to the head. I simply loosened the screw clamp on the rubber pipe enough that I could move the carburetor to the rear. I suppose that it would have been a little easier if I had removed the air filter box but I am not sure. Once the carb is back far enough that you have some clearance, remove the four large nuts that secure the head. Then remove the two small nuts underneath which take the 10mm wrench. There is one at the rear underneath the carb and one at the very front of the cylinder head. This is a good time in the process to remove the camshaft. Use the procedure in the manual to disable the spring tensioner for the cam chain..it is straight forward. Then remove the bolt from the right side which holds the black plastic chain tensioner guide. Hold onto the guide so that it does not fall into the crankcase. Pull it upward once the bolt is out of position and set it aside with the bolt. Next, use a chisel or screw driver to carefully bend the soft steel keeper washer assembly that secures the two camshaft sprocket bolts to the camshaft. The object is to bend the washer tabs down so that you can remove the bolts. Be really careful here when you remove the bolts because it would be easy to drop the bolts into the crankcase as well as the keeper washer assembly. I suppose you could fish them out with a magnet but it is a lot easier to just not let them fall into the engine! Once you have removed the bolts and the two bolts and the keeper, you will find that the sprocket can be moved to a position where you have enough slack to remove the camshaft...Do not drop the little steel half ring that positions the cam shaft in the bearing bore! Again, it could probably be fished out with a magnet but who wants to take the chance. That being accomplished, you are ready to remove the cylinder head from the cylinder. Grasp the cylinder head with both hands and gently but firmly pull upward. Again, there is room to maneuver the head out under the top frame member but not much..just go carefully and try not to scratch paint on the frame tube. Once you have done whatever you wanted to do to the head..and made any repairs necessary, installation is pretty much the reverse of what you did to get it apart. I strongly recommend the Hylomar jointing compound in the tube as a dressing for the new head gasket and also the gasketless valve cover. Put the black plastic tensioner guide back in, install the bolt and torque it snugly but not too tight.
When you reinstall the camshaft, make sure that you position the T mark in the left engine case hole and line the white mark up at 9:00 o'clock. You push the bike in gear a little bit to get the sprocket bolts in a position where you can get a wrench on them to tighten them up snugly. Make sure to bend the tabs up enough so that they will keep the bolts from coming loose. Make sure that the half ring is back in the groove in the bearing bore. Be careful with torqueing the 6 nuts which secure the head. Make sure you fill the little well under the cams with engine oil...you don't want any dry starts here!! This is an excellent time to take a break..carefully check that everything that you have done is OK. You are about to put the valve cover back on and you want everything to be perfect before proceeding...Once you are sure that everything is positioned OK and that you have properly torqued the six nuts and the sprocket bolts are secure with the tabs. Again check that you filled up the little rectangular oil well underneath the cam shaft lobes! Before you try to install the valve cover, make sure that the two lobes are pointed downwards...rotate the engine by pushing the bike in gear to accomplish this. Then make sure that the parting surfaces on the head and the bottom of the valve cover are clean and dry..no oil here!! Remember, this is a gasketless design so you need to use a sealant here..RTV will work, but you are better off with the Hylomar that you also used on the head gasket or you can use the Suzuki recommended product. Just remember to put on a very thin layer and do not overdo it. Remember to put it on all the parting surfaces..it is important to use it on the parting surfaces that form the camshaft bearing..this is important for preventing loss of oil pressure. Carefully maneuver the valve cover back onto the top of the engine and install the retaining bolts in the correct positions and carefully torque. An additional note here is the installation of the three bolt mount which connects the head to the top frame member; Make sure you get these three bolts as tight as you can without breaking them or stripping the threads...I am not sure of the correct torque but this is important because if they are not tight enough, the vibration will wear marks in the bolts and you may find that there is more noise and vibration when riding than you are accustomed too. If this happens, you will find rust powder around the assembly when you remove the bolts and nuts... Anyway, put the exhaust system back on...you can probably reuse the old gasket washers but it is good to have a couple in stock just in case they leak..they are cheap...put the carb back on, install the tank and make sure to connect both hoses! Do a good final check and you should be good to go...You normally do not have to readjust the valves right away after doing a head gasket replacement but this is based on using a gasket with the same thickness as the old one...Before you put the little valve access covers back on, you can make a quick check. Again, rotate the engine crank in the normal direction of rotation using your finger over the spark plug hole to tell you when the piston is on the compression stroke. The valves are closed when the piston is near top dead center. Reach into the little valve access ports with your fingers and insure that you can feel some some free play. If not, you need to set the clearance before you start the engine..you do not want to risk burning any of the valves. If you do have some play (slack), it is safe to run the engine but it would be a proper procedure to set the clearances with a feeler guage after running a couple of hundred miles....

I hope this helps!

[wdnavion]

I am adding this info to hopefully reduce some confusion regarding the head gasket replacement procedure..

As I stated in the forum, there is not a lot of room between the top member of the frame and the top of the valve cover. If I were going remove the cylinder head again, I would probably use some thin wire ties or possibly some plastic tape to get the wiring harness up on the side of the frame member to get a little more clearance. I think I stated that you want all the valves to be closed when you remove or install the valve cover. This is because the valve springs will push the valve cover up making it difficult to remove and next to impossible to re-install. So the easy way to know that the valves are closed is to remove the spark plug and put the bike in a higher gear and put your finger over the spark plug hole. Slowly push the bike forward until you feel the air pushing out. When you feel the pressure dropping that means that you are at near top dead center and the valves will all be closed. Then you can remove the valve cover. Once you have removed the cover, it is a good time to establish the timing marks so that you will have confidence that you are getting them right when you put the engine back together. Remove the threaded plug in the top of the left hand engine case. Use a flashlight if necessary, but look straight down into the hole as you rotate the engine forward...again you can slowly push the bike forward in 4th or 5th gear until the T mark with the gray paint (in my 2002 bike anyway) is centered in the hole. At that time, if you view the camshaft sprocket from the right hand side, you should have the scribed and white painted mark at precisely the 9:00 position...

Moving on to removing the head, remember that you have to remove the four bolts which mount the exhaust pipe collars. Once you have done that, you will most likely find that you have to remove the single muffler mount bolt under the muffler at the right rear of the bike. Move the pipes forward enough so that there is some clearance when you are ready to remove the head. Then remove the carburetor. I did not remove the screws attaching the adaptor to the head. I simply loosened the screw clamp on the rubber pipe enough that I could move the carburetor to the rear. I suppose that it would have been a little easier if I had removed the air filter box but I am not sure. Once the carb is back far enough that you have some clearance, remove the four large nuts that secure the head. Then remove the two small nuts underneath which take the 10mm wrench. There is one at the rear underneath the carb and one at the very front of the cylinder head. This is a good time in the process to remove the camshaft. Use the procedure in the manual to disable the spring tensioner for the cam chain..it is straight forward. Then remove the bolt from the right side which holds the black plastic chain tensioner guide. Hold onto the guide so that it does not fall into the crankcase. Pull it upward once the bolt is out of position and set it aside with the bolt. Next, use a chisel or screw driver to carefully bend the soft steel keeper washer assembly that secures the two camshaft sprocket bolts to the camshaft. The object is to bend the washer tabs down so that you can remove the bolts. Be really careful here when you remove the bolts because it would be easy to drop the bolts into the crankcase as well as the keeper washer assembly. I suppose you could fish them out with a magnet but it is a lot easier to just not let them fall into the engine! Once you have removed the bolts and the two bolts and the keeper, you will find that the sprocket can be moved to a position where you have enough slack to remove the camshaft...Do not drop the little steel half ring that positions the cam shaft in the bearing bore! Again, it could probably be fished out with a magnet but who wants to take the chance. That being accomplished, you are ready to remove the cylinder head from the cylinder. Grasp the cylinder head with both hands and gently but firmly pull upward. Again, there is room to maneuver the head out under the top frame member but not much..just go carefully and try not to scratch paint on the frame tube. Once you have done whatever you wanted to do to the head..and made any repairs necessary, installation is pretty much the reverse of what you did to get it apart. I strongly recommend the Hylomar jointing compound in the tube as a dressing for the new head gasket and also the gasketless valve cover. Put the black plastic tensioner guide back in, install the bolt and torque it snugly but not too tight.
When you reinstall the camshaft, make sure that you position the T mark in the left engine case hole and line the white mark up at 9:00 o'clock. You push the bike in gear a little bit to get the sprocket bolts in a position where you can get a wrench on them to tighten them up snugly. Make sure to bend the tabs up enough so that they will keep the bolts from coming loose. Make sure that the half ring is back in the groove in the bearing bore. Be careful with torqueing the 6 nuts which secure the head. Make sure you fill the little well under the cams with engine oil...you don't want any dry starts here!! This is an excellent time to take a break..carefully check that everything that you have done is OK. You are about to put the valve cover back on and you want everything to be perfect before proceeding...Once you are sure that everything is positioned OK and that you have properly torqued the six nuts and the sprocket bolts are secure with the tabs. Again check that you filled up the little rectangular oil well underneath the cam shaft lobes! Before you try to install the valve cover, make sure that the two lobes are pointed downwards...rotate the engine by pushing the bike in gear to accomplish this. Then make sure that the parting surfaces on the head and the bottom of the valve cover are clean and dry..no oil here!! Remember, this is a gasketless design so you need to use a sealant here..RTV will work, but you are better off with the Hylomar that you also used on the head gasket or you can use the Suzuki recommended product. Just remember to put on a very thin layer and do not overdo it. Remember to put it on all the parting surfaces..it is important to use it on the parting surfaces that form the camshaft bearing..this is important for preventing loss of oil pressure. Carefully maneuver the valve cover back onto the top of the engine and install the retaining bolts in the correct positions and carefully torque. An additional note here is the installation of the three bolt mount which connects the head to the top frame member; Make sure you get these three bolts as tight as you can without breaking them or stripping the threads...I am not sure of the correct torque but this is important because if they are not tight enough, the vibration will wear marks in the bolts and you may find that there is more noise and vibration when riding than you are accustomed too. If this happens, you will find rust powder around the assembly when you remove the bolts and nuts... Anyway, put the exhaust system back on...you can probably reuse the old gasket washers but it is good to have a couple in stock just in case they leak..they are cheap...put the carb back on, install the tank and make sure to connect both hoses! Do a good final check and you should be good to go...You normally do not have to readjust the valves right away after doing a head gasket replacement but this is based on using a gasket with the same thickness as the old one...Before you put the little valve access covers back on, you can make a quick check. Again, rotate the engine crank in the normal direction of rotation using your finger over the spark plug hole to tell you when the piston is on the compression stroke. The valves are closed when the piston is near top dead center. Reach into the little valve access ports with your fingers and insure that you can feel some some free play. If not, you need to set the clearance before you start the engine..you do not want to risk burning any of the valves. If you do have some play (slack), it is safe to run the engine but it would be a proper procedure to set the clearances with a feeler guage after running a couple of hundred miles....

I hope this helps!

[Water Warrior 2]

Wow, that is a fine write up. Obviously you learned by doing and planning. Let's hope the powers that be make a sticky in the How To's as a permanent record. :2tup: