250SX Timing Chain

[GSUwhiskers]

YOU ARE THE MAN! Thank you very much! I'm at a disadvantage because I can't work on it right now so I'm having to look up everything about these parts before even being able to look at the physical parts. I plan on taking many pictures and when I'm done posting a master thread for all newbs such as myself with pictures and an extensive walkthrough. SO do I put the sealant on the bottom of the head before I put it back on the engine? OR just one the top of the head where the rocker cover sits on it?

[GSUwhiskers]

ONE MORE question, when you said I need to roll the CAM sprocket to align the two marks on the sprocket with the head... When I roll the sprocket, won't it move the mark on the flywheel? or no?

[Flyingw]

The bottom of the head (cylinder/head) surface gets a metal gasket. The top of the head (head/rocker cover) gets sealant. That's because of the close tolerance of the CAM journals. When the motor was manufactured, the head and rocker cover were mated together then the CAM journals were machined so the head and rocker cover are a mated pair.

[GSUwhiskers]

Okay, great. So far that covers what I think I need to know haha. I may get into that job and then be right back here asking more questions. Thank you so much for your detailed answers.

[Flyingw]

No, at that point the CAM is poked through the sprocket but the sprocket is sitting loose on the CAM so there is slack in the chain. I lift the chain and roll it around the sprocket until the sprocket rotates to the right place then the sprocket is set on to the CAM and bolted up. Just remember to frequently check the mark in the stator cover to ensure it still in the right place. It helps to leave the spark plug out so the engine isn't being moved by the compression. Later tonight I'll pull a head CAM, chain, and sprocket and give you some illustrations on how all this goes together but that will be later tonight.

[GSUwhiskers]

THAT would be PERFECT!!! You say it so nonchalant, haha, I'm looking all over the place and studying everything just to have an idea of how to go about taking this engine apart.

[GSUwhiskers]

Does the carb have to come off to get the head off? AND does the head have to come off to install the second chain guide?

[GSUwhiskers]

Also, is the CAM shaft bolted down?

[Flyingw]

If you are just replacing the CAM chain, you don't need to remove the head, just the rocker cover. The cam does not get bolted in. Its retained by the journals.

[Flyingw]

Unfortunately I don't have a CAM chain so imagine the pics with the chain on the sprocket. What I'm showing here is the CAM sprocket and how the center is cut out. In a nutshell, you are going to hang the chain over the sprocket with the tallest of the sprocket notches up and down.

[Flyingw]

Now you are going to install the CAM through the sprocket with the CAM turned 90deg so the flanges are horizontal.

[Flyingw]

Now lift the front of the CAM and install the plastic cap.

[Flyingw]

Now rotate the CAM so the lobes are down. The flanges on the CAM are up and down.

[Flyingw]

With the CAM lobes down, double check the mark in the stator cover and ensure its right on the mark. Now you can let you sprocket down and lift the chain and roll it one link at a time until you get the marks on the back of the sprocket to align horizontally with the top of the head.

[Flyingw]

If everything is aligned right, the mark in the stator inspection hole will be on the mark, the CAM lobes are down, and the marks on the back of the sprocket align with the head. Now the hard part. set the sprocket on to the flange of the CAM. The top bolt hole will align perfectly to accept the bolt. You may have to take a screwdriver on the front side of the sprocket and pry up on the sprocket with the chain on it to get it to slide on the CAM. The sprocket should sit flush against the flanges of the CAM. Once the sprocket slides on to the CAM, install the top bolt and snug. Now you can rotate the engine to get the bottom bolt in. Tighten both bolts. Ensure your sealing surfaces on the top of the head and bottom of the rocker cover are clean and free of old sealant. Apply a generous bead of sealant all the way around the top of the head and set the rocker cover on the head and install the bolts and tighten in a criss cross pattern. Chapter 6 of the Honda manual outlines what I just talked about. Install the tensioner. You may need a new base gasket. You have to pull the screw on the end of the tensioner and with a screwdriver turn the tensioner CW to retract the tensioner. You have to hold it that way while you install it because one you let it go, it will extend on its own. The last thing you want to do it to adjust the valves. The motor will already be setup for this so just put the mark in the window of the hole in the stator cover as you did when you installed the CAM. Adjust the valves per the manual.