Engine Piston Height
- Thread starter dalehowe
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I don't know what you could do to change the height the piston is coming up. However the sleeve is another question. The sleeve is to be from .0002 to .003" above the block. Does yours fall in that range?
Another interesting bit of information is the block bores should be marked A, B, or C. Liners will also be marked A, B, or C. This mark should be on the camshaft side of the block. A is larger than B, B larger than C. When I say larger I am referring to block bore deminsions. Nothing to do with your question but I had not seen this before. So you guys changing liners need to remember that to assure getting the correct liners for your engines. Woe is me, my YM2002D has no liners.
Let me clarify a little more. This information is out of a service manual for a YM276, engine 3T84HA.
Another interesting bit of information is the block bores should be marked A, B, or C. Liners will also be marked A, B, or C. This mark should be on the camshaft side of the block. A is larger than B, B larger than C. When I say larger I am referring to block bore deminsions. Nothing to do with your question but I had not seen this before. So you guys changing liners need to remember that to assure getting the correct liners for your engines. Woe is me, my YM2002D has no liners.
Let me clarify a little more. This information is out of a service manual for a YM276, engine 3T84HA.
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My 336 book which is incorrectly listing the 3t90 in all its specs (rather than 3t84) says liner above deck is .003-.006".
I believe the 2 are interchangeable in that spec from what I saw in mine and my pistons were above the liners also. I didn't measure them but they were above and my liners were equally set at .005-.006" which I did measure.
My opinion is this-if the liner is at that height and it ran before it has to be ok thats my common sense answer. Now thats unless someone has line bored the living heck out of the main bearing bores and thats highly unlikely it would even be measurable at the deck.
Look at it like this-The head gasket is another probably .035- .045" guessing compressed so there is clearance. I know .019" isn't an interference concern with the head deck anyway. Maybe the pre-chambers depending on whats been done to the head however. fwtw
I believe the 2 are interchangeable in that spec from what I saw in mine and my pistons were above the liners also. I didn't measure them but they were above and my liners were equally set at .005-.006" which I did measure.
My opinion is this-if the liner is at that height and it ran before it has to be ok thats my common sense answer. Now thats unless someone has line bored the living heck out of the main bearing bores and thats highly unlikely it would even be measurable at the deck.
Look at it like this-The head gasket is another probably .035- .045" guessing compressed so there is clearance. I know .019" isn't an interference concern with the head deck anyway. Maybe the pre-chambers depending on whats been done to the head however. fwtw
Welcome. The reason I mentioned the pre-chambers is my head was warped pretty bad it measured .009" and they took the minimum off (no idea what that was 10-12 thou probably) they could because I wanted it that way.
I had concerns with the close proximity of the rest of the combustion chamber though (you will see what I mean) and didn't want to go about assembling and claying the pistons etc.
So I added an extra copper shim .020" approx under each of the chambers to take up that that was milled off and it worked great. The specs I remember finding said NOT to mill the head but I rarely pay attention if I have a solution.
Domush
Platinum Member
I was just wondering about this exact same scenario on my 336. I love this forum.
Domush
Platinum Member
Well, if it helps you any, my pistons come up .018"-.019" above the deck (not the liners, as they are not all the same on mine).
So, if you compare yours to mine, they are normal. Though I haven't found much normal about mine, hehe
So, if you compare yours to mine, they are normal. Though I haven't found much normal about mine, hehe
284 International
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- International Harvester 284
Do you think the resized rods are causing the pistons to protrude too far? I'm surprised there isn't a specification somewhere for this dimension.
What you must be joking????
I cant begin to explain how many ways that is wrong seriously wrong.Here is a pic of my engine when I had it down sorry I didn't measure the actual piston height for posterity and it doesn't show a side view.
I knew it had to be ok because it ran fine up till the HG blew which was the engine builders (hack) mistake of not checking or letting it slide the fact the head was out .009".
It is common btw for diesels to have pistons above the deck/liners that is how you get 20+ to 1 compression.
I had to turn the crank so the pistons were down to measure my liner heights (that what I am doing in the one pic) because the pistons are above the liners like I mentioned .019" sounded ok to me that you say yours are.
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shawnjvl
Silver Member
When I had my 2000 apart, I seem to remember the pistons were definitely above the deck.
careyo63
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We have to keep valve timing in mind these diesels have pretty lazy valve timing and dont need very aggressive cams to run right and to be able to make the high compression they do and have to have to live.
The 4 cycle diesel operates different than 4 cycle gas and as such doesn't need a bunch of added valve timing to get a complete burn/full cylinder at higher speeds gas engines run at.
The possibility of a valve hitting a piston is slim to none still after .010-.020 is taken off imho just because the valves are not open anywhere near TDC.
My experience with Yanmar is limited to my tractor but his 336 is basically the same and my valves were below the head deck by a fair amount and after grinding valves and seats its even further under the deck. So thats why I believe they will never touch, if they were above the head deck which I doubt they are the story may be different. fwtw (my pre-chambers were above the deck by a good bit and Id say better than .020 just for conversation they never hit before or after milling and is the main reason I added an extra copper seal ring)
Consider our compression releases for instance...they hold the exhaust valve open all the way thru the cycle granted you could possibly adjust them enough so they hit but you take the cam out of the equation and hold them open is what I am getting at there.
And dont get me wrong I dont have facts to back that up just my gut feelings knowing engine manufacturers as well as I do.
The 4 cycle diesel operates different than 4 cycle gas and as such doesn't need a bunch of added valve timing to get a complete burn/full cylinder at higher speeds gas engines run at.
The possibility of a valve hitting a piston is slim to none still after .010-.020 is taken off imho just because the valves are not open anywhere near TDC.
My experience with Yanmar is limited to my tractor but his 336 is basically the same and my valves were below the head deck by a fair amount and after grinding valves and seats its even further under the deck. So thats why I believe they will never touch, if they were above the head deck which I doubt they are the story may be different. fwtw (my pre-chambers were above the deck by a good bit and Id say better than .020 just for conversation they never hit before or after milling and is the main reason I added an extra copper seal ring)
Consider our compression releases for instance...they hold the exhaust valve open all the way thru the cycle granted you could possibly adjust them enough so they hit but you take the cam out of the equation and hold them open is what I am getting at there.
And dont get me wrong I dont have facts to back that up just my gut feelings knowing engine manufacturers as well as I do.
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Minimum quench distance on a high performance automotive gas engine is 35 to 40 thou. Factory tolerance is usually between 60 and 100 thou., but with stricter emissions and higher compression ratios this number is closer to the 35 number.
These little diesels run much tighter than that because of the limited rpm they see and the small bore. Personally I would go no tighter than 20 thou.
You can absolutely have the pistons tops milled, if you determine you do not have enough clearance. It's done all the time. It is up to you to take the proper measurements though, and use the compressed thickness of your head gasket for your calculations.
If it's strictly for the prechamber interference, you can clearance the piston with a dremel and a steady hand. You're only taking the equivalent of the amount of head milling that was done, which is easily achieved.
As to the question about the rod reconditioning changing the piston height, If the job is done correctly the center to center dimension of the rod does not change. Therefor the quench distance should remain the same.
These little diesels run much tighter than that because of the limited rpm they see and the small bore. Personally I would go no tighter than 20 thou.
You can absolutely have the pistons tops milled, if you determine you do not have enough clearance. It's done all the time. It is up to you to take the proper measurements though, and use the compressed thickness of your head gasket for your calculations.
If it's strictly for the prechamber interference, you can clearance the piston with a dremel and a steady hand. You're only taking the equivalent of the amount of head milling that was done, which is easily achieved.
As to the question about the rod reconditioning changing the piston height, If the job is done correctly the center to center dimension of the rod does not change. Therefor the quench distance should remain the same.
