Piston to head clearance

tim s

Well-known Member
Can any one tell me what the piston to head clearance should be on a 4240, I have one that had been lined bored and don't know how much was taken up,,it seems to be decking a bit too high,,and yes I looked in the tech books, they don't discuss this,,Darn it..
 
Not sure what it should be, but my IH D-282 I rebuilt it on purpose last winter at .028-.030 inch piston to head clearance. Was going after all the compression heat I could get. Some small air cooled diesels are set close as .025 inch, didn't want to go quite that close..
 
One more thing to check, could be more critical than the deck. How tight is the crank/cam gear clearance? If block had enough line bore repair shift to affect the deck, gears may be way too tight..
 
This one is about .002,,it's noisy at high idle,tried a bit thicker head gasket,,didn't help,,I'm about to have .040 milled off of them...it spun a couple main's and was line bored but no one kept notes on how much was taken away...I'm thinking most of the noise is pre-ignition knock..it's too loud to ignore...it's in a 4050/466, and has a turbo added..
 
If I recall that should have the Stanadyne DM pump on it, could be issues with the advance in the pump. Have seen them break cam pins also, but that will retard the timing and get quieter. If the pump advance curve is OK, might be worth a try to retard the static timing a bit. Last one I had in needed the oversized advance piston installed, when the housing to piston clearance is great enough the advance won't move, and return oil gets high. Changing the vent wire won't help when it's that worn.
 
Pump was rebuilt last year,it should be okay,noise show ed up after o/h,that's why I'm looking at piston hieghth
 
Didn't know diesels could have pre-ignition knock??? Timing too far advanced???

Any race car buddies have info on piston to deck height?
 
Spec shows pump has 9 degrees total advance for 18 at the crank. Years ago had the same trouble with a turbo kit installed on a late model Ford 5000, noisy, and low power with the CAV DPA rotary pump. Dealer had good results with the same turbo kits on early tractors, but those had inline pumps set at 23 degrees static timing, and no advance like the rotary pumps had. Dealer found the rotary pumps were running close to 40 degrees advance, much more than needed. What helped was removing the pump 9 degree advance piston and installing a 3 degree piston. Power came back, and noise was more like the early inline pump engines had. May be wishful thinking, but retarding the static timing 5 degrees could be worth a try before major engine surgery is done.
 
I did that before I pulled the head..all was well before the line bore,,and I'm sure the pistons are too high,just not sure of how much to shave...
 
Would not think the line bore repair could have raised the crankshaft very much if the crank/cam gear lash is not tight. Another thought is to do a compression test and see what it is now, does not take much off the piston top on diesels to change the ratio, compared to gas engines. Probably starts great now, I'd hate to give that away. Any chance the piston bowl chambers are smaller than the old pistons?
 
(quoted from post at 20:38:24 07/11/17) Can any one tell me what the piston to head clearance should be on a 4240, I have one that had been lined bored and don't know how much was taken up,,it seems to be decking a bit too high,,and yes I looked in the tech books, they don't discuss this,,Darn it..

Assembling with a ball of lead shot on the top of each piston , The turning the engine by hand will squash the lead flat which allows mic'ing to find actual true cold clearance.
Hot running, red line rpm clearance is as close as possible without smacking pistons into the head.
Ideally injection and cleanest, most efficient combustion takes place in the piston bowl as much as possible instead of across the top of the piston, According the theory.........................
 
Liners bolted down,dial indicator to prove TDC,,straight edge across the liner,,feeler gauge to measure clearance,,next to no clearance,,I don't want to shave too much,,but I want to get it right,,I haven't had issues like this since we quit pulling back in the 70's,,Darn it
 

How thick is the stock factory head gasket ?Any indication of the pistons touching the head ?
While barely related, the small block chevy quench style cylinder head calls for 40 thou clearance or less to obtain proper squish and turbulence .
I'm with the other posters thinking some manner of early injection event ???
 
Line bore issue..brought the crank up too far,,and i don't know what the dimensions were,,so..I'm getting ready to send the pistons to the machine shop for a shave,,right now I'm thinking about .030"...I know i'm rolling the dice here..
 
how thick is the head gasket ? 40thou cold clearance of head gasket plus piston deck below the liner/sleeve should be close .
 
Just got off the phone with the tech guy from Reliance,,he was very knowledgeable, and helpful,,but he could not come up with the dimension I was looking for,,checked the numbers my pistons are correct,,I am at less than .001 clearance when TDC..I'm removing the pistons now and going to have .040" milled off of them..we will see..
 
A major/big time machine shop will have piston height specs.Horn Automotive Ceder Rapids Ia. (319)231-0252 or Abraham's Machine, Davenport Ia (800)553-8990 A mistake I used to do was only measuring piston on one side not taking into account rocking motion at pin.
 
Yes. I was considering the rocking action too,,I'm going with .060",,it's happening now....
 
Stop everything, go get some Bud, and think about this, be awful hard to put .025 back on top of pistons. Was it 90 degrees/humid in your shop today like mine? lol
 
If they moved the center of the crank shaft up in the block more than .010 or .015" you are going to have more problems than piston to head clearance timing gears clutch alignment ect.If the rods have had big end reconditioned they will be shorter than stock??.an absolute minimum of maybe .020-.025" piston to head .

I have run some small blocks pretty hard at.027" the old school recomendation on automotive is .040" and those forged pistons have a tendancy to rock in the bore more than a long skirt tractor piston.

if you shave pistons down too much it won't start.Paul
 
(quoted from post at 19:21:15 07/12/17) If they moved the center of the crank shaft up in the block more than .010 or .015" you are going to have more problems than piston to head clearance timing gears clutch alignment ect.If the rods have had big end reconditioned they will be shorter than stock??.an absolute minimum of maybe .020-.025" piston to head .

I have run some small blocks pretty hard at.027" the old school recomendation on automotive is .040" and those forged pistons have a tendancy to rock in the bore more than a long skirt tractor piston.

if you shave pistons down too much it won't start.Paul

I was thinking the same but was scared to say it . If the head gasket is 20thou then also cut the pistons 20 thou and make the total 40 thou cold .
 
I know what your saying Paul,, I have been thinking this over for 2 days..the cam gears were nice,,liner protrusion was good,,pistons were coming up at less than .001",,my guy is cutting them now,,going back together tomorrow...It's been well used over the years and this guy bought it used a couple years ago..
 
Ooh yes Glenn,,I've been mauling this around,,made the move today my guy is on the 5th one now,,the owner needs it..and I need to be working on my Rantual projects now so the paint is not drying on the way out there...4 more tractors to finish yet, and then I'm gonna quit answering the phone ;^)
 
(quoted from post at 20:36:28 07/12/17) Ooh yes Glenn,,I've been mauling this around,,made the move today my guy is on the 5th one now,,the owner needs it..and I need to be working on my Rantual projects now so the paint is not drying on the way out there...4 more tractors to finish yet, and then I'm gonna quit answering the phone ;^)

Tim. The problem is that you can revive cases beyond other mechanic's ability, now
everybody wants your work.
 
Piston height is measured from top of block, not sure what is gained by measuring piston to top of sleeve?
 
Just asking a dumb question ,but were the pistons installed the right way ? I had a 3020 with pistons in backwards and it ran terrible .
 
Yes they were in correctly,, I have been double checking all the dumb stuff..... dropping the shaved pistons in now..
 
I'm also confused...but I do know the pistons were coming up too far..but not now..
 
Okay I still don't fully understand why,,but I peeled .060" off the pistons,,it sounds great now and starts good,,more things that I don't understand..Darn it
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Maybe the aftermarket pistons were made wrong ? Or was the crank reground and maybe they got the rods offset for wrong stroke ?
 
I matched the pistons to the old ones,, they were exactly the same,,rods were done by the shop I always use,,I feel good on that..line bore is the only thing that I can point to...It's out the door now heading to the hay field now...sounding great..just like it should...I also checked the cam gear it still had a little back lash...was not tight...
 
Those are nice to work with,, and we Got stuff to get ready for Rantual.. That tractor was mowing hay all day today, the guy is happy with it...
 

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