Piston thrust side and Desaxe

[hydrolastic]

Hello Guru's, For various reasons i have been thinking of building a Desaxe bored engine. Desaxe as i understand it is moving the cylinder centerline over away from the crankshaft. My application is only about .070. I noticed though that the thrust of the piston up the bore varies. in other words at the bottom of the 4" bore its still 4" but the bore wears to a lip on top of the thrust side of the cylinder. I was wondering if just the top of the bore was moved over (.070) and the new centerline was from the crank main center to the new top of the bore center. basically tilting the bore centerline. Is this a Desaxe engine or just a tilted bore centerline? also for timing the ignition what is tdc. Is it when the crank is sraight up or a few degrees moved over? Hydro

[PackardV8]

For those, like myself, who had no referent for the term; https://en.wikipedia.org/wiki/Desaxe

After reading the citation, I realized I'd seen them around forever, i.e. flathead Ford V8, but never heard them called by that term.

Many engines with centered crankshaft/cylinder axis use offset piston pin bores to reduce cold slap upon startup. Supposedly reversing the offset increased power production, but I was never able to measure it. Many race builders spend time insuring cylinder bores are centered with respect to the crank bore and use pistons with no offset.

Those more advanced than myself will have to debate if the slight movement (.070") you contemplate will make any discernible difference.

[Tom Walker]

I believe Toyota was and may still be doing it with more than just the Prius engine.

[hydrolastic]

Thanks Jack. I like reading your posts. To be more clear, The reason i want to move the bores is to put a completly different head on the engine and if i can move the bores a bit i can use a portion of the existing head studs. I also have wanted to try a desaxe engine design forever!

[modok]

TDC is when the rod forms a straight line to the main bearing centerline. It is when the piston pin is farthest from the crank.

Offsetting the cylinder that much should be ok. It is no different than pin offset. .040-.060 pin offset is quite normal.

[modok]

I was wondering if just the top of the bore was moved over (.070) and the new centerline was from the crank main center to the new top of the bore center. basically tilting the bore centerline.

In that case the piston would not come up square to the head, Is this oK?

[DCal]

Similar to a 409 Chev and 430 Lincoln combustion chamber wise? I would like to see pin offsets in the .125 area if we're doing offset vs centered tests again. The biggest reason we don't do more than .060 is because custom piston manufacturers don't design forgings with extra thick pin bosses. The extra 20 grams for the thicker pin bosses just isn't worth it for one piston order out of 5-600 orders that require the offset.