I'm not sure I am asking the question correctly, but here goes. Does anyone have the clearance spec between the piston top and the valves at TDC? Asked another way, how far below the top of the cylinder should the top of the piston be at TDC?

Thanks for your help!

Dont have an answer but I lost your phone number. A good friend is looking for a harmonic Damper for a 466 engine. Could you contact (message ) me if you have a spare.

not sure why nobody has responded to your question but maybe i can get the ball rolling...

-the top of the block i call the Deck, so piston height at TDC, to the top of the deck distance...clearance etc... measured in thousandths of inches...
-normally that is very close, esp in gasoline engines....diesels i'm not so sure...everything is designed around clearances, head design, piston design, deck clearance, valve to piston clearances, gasket thickness to get proper compression ratio etc...lotsa factors to be aware of...

-this is why when you true up a block deck, or resurface a cylinder head, you remove the absolute minimum that will clean up the piece..

-perhaps you can post a couple photos and explain why you want/ need to know?

like Neil says, that might not be a spec that's often published, most rebuilders doing a straightforward engine rebuild wouldn't require that spec. As long as you have the correct parts you would just assemble and everything works out.

-another side note, the distance above the piston and head at TDC, is also called Quench, or Squish in a gasoline engine. It helps create turbulence and a better mixture for better combustion etc. Some people think it is really critical, others not so much. I think the magic number was approx .030", not much at all. How important this would be with a diesel I have no clue.

Hi Team,
I also do not know the top deck to piston crown spec. dimension, if ever published, for these Cat engines --some later engines the distance from the crank centre line to the top deck is given--I do know that a few well used blocks we rebuilt had the piston crowns shaved to suit the below spec. dimension to keep things standard. Cat had a maximum amount removed from a stock dimension on the later engines that they considered the block was not safe to re-used due to too thin a liner counter-bore base metal to not crack and also not have valve head to piston interference.

On some blocks that have been over decked the Valve to piston clearances need to be checked and would be considered more critical than the piston to deck dimension and we had some piston valve pockets deepened to gain some effective clearance--sorry I do not recall what if any spec that might be but something in the order of a minimum of 0.020" to 0.030" would likely be safe as our outside engine machinists did this work and likely got the data from our Dealer Technical Service Dept. via Caterpillar and so was corporate info. and so not for general knowledge.

Cat have tight specs for valve head protrusion above the cylinder head surface as noted in the Valve Seat Spec. Charts--some heads have sunken valves.
The danger of piston to valve clash occurs at Top Dead Center (TDC) piston travel with both the Valves on overlap--both valves open and also just before and after TDC as the valves are either opening or closing dependent on if we are checking the Exhaust or Inlet Valve motion.

( was Mother's Day here down-under yesterday so was not on the confuser to answer.)

Hope this helps.
Cheers,
Eddie B.

Put some modelers clay on the piston and valve area and replace the head with an old head gasket and see what you get for clearance. I'd be more comfortable with about 0.050" clearance but you can probably get by with less.

there ya go, tons of great info...i knew youz guys were holding back on me....

-probably biggest concern would be valve to piston clearance, and .050" is a ton (correct MrMagnet)

-so unless somebody got crazy removing metal you should be Golden (aka, new Cat Yellow)

The D4600 engine has a flat head with valves that protrude below the head when closed. There is a recess in the pistons to accommodate the valves. From memory when I had the heads off the D6 the pistons at top dead center were very close to flush with the top of the cylinder sleeve top. The head gasket is fairly thick and there is also a combustion recess in the piston that will give the correct compression. I have a service manual for the D6 5R/4R series but it does not list the clearance nor does it list the recommended compression. As OM said .050" would be pretty close. I think that would be about gasket thickness. Also OM talked about using an old head gasket, unless the gasket is damaged on removal or in storage it is quite OK to reuse them multiple times. I have seen the same head gasket reused six times and is still in service. Wouldn't try that on later machines.

Kittylover123
The clearances in a diesel are much less than a petrol engine. Diesels compression is much higher 22:1 whereas a petrol engine is only 8:1-9:1. The higher compression is required to allow the fuel to ignite when injected.