I am here to tell you he is right.
Mine were all shot, with tolerances in the single digit millimeters range as opposed to 0.05mm to 0.09mm. That's two orders of magnitude off. No wonder I could not keep valve clearance stable and the bike was burning oil and pinging under heavy load.
Disclaimer: I rebuild my first engine at fourteen. My dad is a mechanical engineer. I have two degrees in engineering. I have replaced the IMS bearing of my Porsche and while at it, I replaced the clutch too. I can do a valve tune up on a Ducati Testastretta engine with my eyes closed. I would advice that you read this for entertainment only and do not attempt it unless you have a similar level of skills. You can do a lot of damage if a valve gets stuck due to improper clearances.
Tips I learned in this project:
1) To remove the old guides, I tapped them at the top, screwed in a suitable screw and drove them out with a hammer and a rod that fit inside the guide from underneath. This way the blow from the strike would go through the screw and the guide and nothing else. Note: I used a heat gun to heat up the area around the guide for about two minutes before driving the guide out.
2) I measured everything several times and had some sanity check with an expert and replaced one of the valves (see photo, the shiniest one is new). The stem can wear so be sure to measure them too. Ironically the one I replaced is not the one from the worst guide so do not assume anything and just measure and measure again.
3) To install, I froze the new guides overnight and heated the area again with the heat gun. I put some assembly lube on the guide and drove them in. It took about if not more effort than to remove them and that sounds about right since it is an interference fit.
4) If you decide to ream by yourself, do it by hand and make sure you have a lot of patience. Forget those clowns on Youtube that use a power drill, you will never get it right and the guide will be blown in a few thousand miles. Unless you have access (and experience) to a high precision drill press, either pay someone to do it or do it by hand if you are an advanced amateur mechanic. I own a drill press but I do not consider it a high precision one so I did it by hand. The drill press needs to be accurate to within fraction of a degree! One of my guides was an oversize that required a lot of reaming, it took easily more than an hour and many dozen runs cleaning, oiling, reaming and repeat.
5) Lapping can be fun and very useful to assess if you succeeded or it is time to take it all to a machine shop. After you lap the valves, you will see a ring around the head of the valve, that ring needs to be close to the edge and about the same size for all valves and all around. Any deviation from it is a sign that the seat/valve combination is off and it is time to kiss some money goodbye and hire a machinist. The actual values depends on the engine, I got 2 to 3 millimeters seal ring less than a millimeter from the edge. Sorry I do not have photos, I wrote this after I reassembled everything. Oh and yes, she runs fabulous, see video below. This was after a short test ride. I have since put about 100 miles.
One more take away: before the valve job, the bike would easily loose 400rpm at idle when hot, to the point that it would die at stop light. Now it idles at near the same rpm at all engine temperatures and it stays on and start right up. You can hear her start in the video after a severe hill climb (very hot engine).
 |
| ready to reassemble, note the new exhaust valve |
 |
| Springs are in, all cleaned and lubed. Note the old dismissed valve in the background. |
No comments:
Post a Comment