Bike won't idle, poor compression.

[Krauser4valve]

Chuey, I have what I believe are set of pistons for the Nikasil cylinders, they have been flycut to lower the compression ratio some unknown amount. You are welcome to them, the appear to be unused.

[the quinner]

Excuse my ignorance on this matter, but could a C size piston be chucked up into a lathe and turned down? Then you could have some of the new space age coatings applied and use it in the stock size Nikasil cylinders, no?

Chuey

Not that easy, Chuey. Pistons are not round to start with, so they end up being round at operating temps. If you make them round to start with, they will go out of round at temp. It's far easier to make cylinders bigger than pistons smaller. The space age coatings can restore some dimension to pistons...but, it's a process that is far more successful with modern slipper pistons than our older coffee can slugs.

[Krauser4valve]

Engine is back together after a honing and new rings (Deves made a custom set). It starts and idles with a small amount of enrichener, much better than before. I took the suggestion to go back to the Champion G63 plugs, the NGK and ND subs were a little shorter and likely shrouded in the chamber. Next up is a ride to work out the bugs and then over to Spannerland to put it on the dyno. I left the lowers off, looks better to my eye.

77rs.jpg (79.27 KiB) Viewed 1452 times

[Chuey]

Carrouser4valve, I hadn't seen your offer as I had forgotten to look at this thread until I saw it here today. Just a few days ago I put my Krauser engined bike up on the stand and have started to Cafe' it.

Are the pistons from Krauser? It would surely be nice if there were more information out there about this subject.

Your bike looks good. I'll be watching to see the results.

Chuey

[Krauser4valve]

I now think they aren't flycut as the bike at the bottom of this page has the same pistonshttp://www.desertpistons.com/4strokesd/ ... rindex.htm. Mine have no dish in them. Maybe Krauser lowered the compression ratio at some point? Yes, they are Mahle-sourced Krauser parts. Near as I can tell, the guy that built my engine used the rings (for a stock bore) from these on my bike (.010 over), which is why it never ran correctly. So, I have the unused pistons and no use for them.

[the quinner]

I now think they aren't flycut as the bike at the bottom of this page has the same pistonshttp://www.desertpistons.com/4strokesd/ ... rindex.htm. Mine have no dish in them. Maybe Krauser lowered the compression ratio at some point?

There were supposedly lower compression pistons available...intended primarily for the US market.

[Krauser4valve]

I guess that's what I have then. Quinner, any ideas on the static timing for these heads? I have the idea that it should be somewhere near a dual-plugged head (retarded some), but that's a guess obviously.

[Garnet]

I guess that's what I have then. Quinner, any ideas on the static timing for these heads? I have the idea that it should be somewhere near a dual-plugged head (retarded some), but that's a guess obviously.

I woud think it should be closer to stock than dual plugged. With dual plugs the flame front starts much faster, hence the need for some retardation. In your case the start of the flame front is just moved to the best position in the combustion chamber, but does not happen any faster. Some small amount of retarding may be needed, but if you look at specs from aother multi-valve engines you will see that several degrees of advance at idle and 30 ish at full are the norm.

[Krauser4valve]

Thanks Garnet, that makes sense. The manual doesn't have any information about it. Speaking of which I bought a pristine version on ebay for $2.50 last week, sweet, I never had a real copy.