Engine Trouble Top Dead Center?

[CrispyLeaves98]

Are our engines supposed to be at the very top dead center of the cylinder? Both of my friends bikes, my yd100, and my Athena don't hit top dead center but many preformance dirt bikes do. Due to me having spacers available I started milling mine down with sandpaper and smoothening it out with like 600 grit.

Is this wrong for my engine?

 

[darwin]

TDC is when the piston is at it's highest point on the combustion stroke.

 

[CrispyLeaves98]

TDC is when the piston is at it's highest point on the combustion stroke.

I'm trying to get it to match with the top dead center of the cylinder itseld

 

[Chainlube]

Measure how far down in the cylinder the piston is and shave down the adaptor plate that amount. Take into consideration your squish gap, it should be .7 to .8mm. You can try a thinner base gasket or one if you have two.

 

[GW's Motorized]

All you are doing is increasing compression. I would do a little research on port timing if you are milling down your cylinder head.

 

[ImpulseRocket]

Take the time to study engines and their terminology if you want to do this kind of work.

As other mentioned, Top Dead Center is the physical limit of the piston extending toward the deck of the cylinder, and more specifically, when the crankshaft pin, rod journal, and connecting rod are all perfectly in line at a 0 degree angle, with the piston at the top of the stroke in the bore.

The actual terminology for the example seen in this video is known as the Deck Clearance. This figure can be both positive, negative, or zero. It's also backwards from what you might think it is. If The height of the deck is zero, anything below the deck height is positive and anything sticking above it is negative. On a vast majority of engines, this figure is positive, and done so intentionally.

The gap between the top of the piston crown and the deck height is a portion of the total factors that calculate the squish gap, which is the total clearance between the edge of the piston crown and the combustion chamber, or deck surface of the head, depending on the design.

I would be happy to go into even more detail if you desire, but please just don't blindly start sanding.

 

[Arty]

Take the time to study engines and their terminology if you want to do this kind of work.

As other mentioned, Top Dead Center is the physical limit of the piston extending toward the deck of the cylinder, and more specifically, when the crankshaft pin, rod journal, and connecting rod are all perfectly in line at a 0 degree angle, with the piston at the top of the stroke in the bore.

The actual terminology for the example seen in this video is known as the Deck Clearance. This figure can be both positive, negative, or zero. It's also backwards from what you might think it is. If The height of the deck is zero, anything below the deck height is positive and anything sticking above it is negative. On a vast majority of engines, this figure is positive, and done so intentionally.

The gap between the top of the piston crown and the deck height is a portion of the total factors that calculate the squish gap, which is the total clearance between the edge of the piston crown and the combustion chamber, or deck surface of the head, depending on the design.

I would be happy to go into even more detail if you desire, but please just don't blindly start sanding.

Nicely explained Impulse. It cleared up my understanding of "Squish" a lot. - - Thanks.

 

[DieselTech]

I thought optimal squish on a minarelli engine was .9mm to 1.1mm

 

[CrispyLeaves98]

All you are doing is increasing compression. I would do a little research on port timing if you are milling down your cylinder head.

Milling down the CNC adapter plate no worries

 

[CrispyLeaves98]

Take the time to study engines and their terminology if you want to do this kind of work.

As other mentioned, Top Dead Center is the physical limit of the piston extending toward the deck of the cylinder, and more specifically, when the crankshaft pin, rod journal, and connecting rod are all perfectly in line at a 0 degree angle, with the piston at the top of the stroke in the bore.

The actual terminology for the example seen in this video is known as the Deck Clearance. This figure can be both positive, negative, or zero. It's also backwards from what you might think it is. If The height of the deck is zero, anything below the deck height is positive and anything sticking above it is negative. On a vast majority of engines, this figure is positive, and done so intentionally.

The gap between the top of the piston crown and the deck height is a portion of the total factors that calculate the squish gap, which is the total clearance between the edge of the piston crown and the combustion chamber, or deck surface of the head, depending on the design.

I would be happy to go into even more detail if you desire, but please just don't blindly start sanding.

Please explain the performance and other effects this has on the engine and why