Im going to take apart my Magnum 91 fourstroke and remove the carbon from the valve, as I have a leak through the exhaust valve. When I re-assemble, is there any particular rule of thumb for how tight to put the cylinder head back on, or do you just tighten them down real good? Any other tips to avoid possible mistakes would be appreciated. I have done this countless times on two strokes, but with the more complex fourstroke, it just seems like everything needs to be perfect. Thanks

Alex

dont forget valve timing also!!

sean

Alex:

Don't worry about valve timing. No neeed to disturb the cam for a top end cleaning. And if you can do the head on a 2s with no problem, it's just the same on a 4s regarding the mounting of the head, if you don't loosen the valve adjusters and put everything back in the original position you might not even have to reset the valves.

One thing. DO NOT use any lapping compound on the valves or seats - after you get the deposits off chuck the valves in your electric drill and lightly polish the seating face with a pencil eraser. Spin the same pencil eraser on the valve seats to clean them, then put it all back together.

Bill.

I too disassembelled my Magnum 91 for a reason I would rather leave unsaid. It's all back together now, and I learned a 'new' technique reassambling the dang pushrod spring keepers *%#$@!! I've just about got it back together, but I need to know how much gap the valves need between the rocker arms. Anybody got that spec?

I believe it's anywhere between .01 and .004.

John

I use one half of one thousandth inch (0.0005") but all the makers call for 0.002" to 0.004" or if you have metric feelers that's 0.05 to 0.10 mm.

Bill.

hey deadeye i seen a sale on epoxy!!!!!

I stand corrected. The valve gaps are .10mm max. and .04mm minimum.

John

There is a 3-hour DVD (aboutENGINES) put out by modelSPORT that does a good job explaining how to dissasemble and reassemble both 2-stroks and 4-strokes. It was worth the $19.99

RCB003 $19.99
aboutENGINES


RCB003 - aboutENGINES

Segments:

1. aboutENGINES
2. Safety
3. Fuel Make-up
4. Fuel Systems
5. Engine Break-in
6. 2-stroke Assembly
7. 2-stroke Break-in
8. 4-stroke Break-in
9. 4-stroke Assembly
10. Adjusting Valves
11. Gasoline Engines
12. Gasser Assembly
13. Multi-cylinder Engines
14. Walbro Carbs
15. Spark Plugs
16. Fine Tuning

Available only on DVD



If my memory is correct, he reseated the valves using toothpast.

http://www.modelsport.com/modules.ph...8a2b7d6df14445