VWDiesel.net The IDI, TDI, and mTDI source.
Engine Specific Info and Questions => IDI Engine => Topic started by: rallydiesel on April 22, 2007, 08:02:18 pm
-
The Bentley manual says diesel cylinder heads cannot be machined if warped. I doesn't say anything about machining the deck. I am pretty sure I have heard of people getting cylinder heads machined. What are people's thoughts about this and why does the Bentley manual say you can't?
-
i guess if the head was really warped then you'd have to get a new head... but you can take off a little bit. just compensate for choosing head gasket thickness with the layer that you took off the head, and there shouldnt be an issue.
some people also talk about the bearings for the cam having trouble when the deck is machined... once the head is torqued down it puts stress on the cam. (say for example the sides of the head are machined... there will be more down force on the ends of the cam...)
but i guess they say that you cannot machine them for the same reason that you have to buy the whole water pump housing... there are just too many people out there who do not know what they are doing!!!
-
Depending on how warped the head has become the cam bearings may need to be alignbored (no different than a gasser head)... the machinist should be able to figure out if this is required.
Some shops will be wary of the precombustion inserts.... some sites say they need to be ground with a stone rather than milled like the rest of the head... but I've read it done both ways.
Either way, if you want to maintain stock compression, the proper gasket to use is still the one the piston height tells you to use !!
Vince
-
OK. Here is a related question: if the camshaft has too much bearing clearance, is a new head pretty much mandatory? I know the bottom bearings are part of the head, but is there a place to get bearing caps or are they matched to the head?
I am asking this because the previous owner left a cam bearing cap in the glove box and I haven't taken the valve cover off yet. I am expecting the worst (no bearing cap or some kind of makeshift jobby).
-
Depending on how warped the head has become the cam bearings may need to be alignbored (no different than a gasser head)... the machinist should be able to figure out if this is required.
Some shops will be wary of the precombustion inserts.... some sites say they need to be ground with a stone rather than milled like the rest of the head... but I've read it done both ways.
Either way, if you want to maintain stock compression, the proper gasket to use is still the one the piston height tells you to use !!
Vince
isn't there a bit of a recess in the head for the cylinders? not much... but enough? if there isn't then yea pretty much what i said above becomes null and void :oops:
-
When they alignbore they remove a bit of material from the top cap and the bottom cap... making the hole smaller. They then bore a new hole the right size all the way thru.
So, if your cam bearing caps have too much clearance this may be an option.
-
When they alignbore they remove a bit of material from the top cap and the bottom cap... making the hole smaller. They then bore a new hole the right size all the way thru.
So, if your cam bearing caps have too much clearance this may be an option.
Wait, how does removing material from the caps make the hole smaller?
-
Imagine you have a chair that your dog can just get under.
Now cut a couple inches off the legs.... the hole gets smaller and your dog can no longer get under the chair !!!
Now think of the cam bearing saddle and cap as two chairs stacked leg to leg... and you get the picture.
Vince (who actually has a dog who can only get under some of my chairs)
-
Imagine you have a chair that your dog can just get under.
Now cut a couple inches off the legs.... the hole gets smaller and your dog can no longer get under the chair !!!
Now think of the cam bearing saddle and cap as two chairs stacked leg to leg... and you get the picture.
Ahh, my thanks. I was mentally removing material from the wrong parts.
-
isn't there a bit of a recess in the head for the cylinders? not much... but enough? if there isn't then yea pretty much what i said above becomes null and void :oops:
It's flat
-
flat flat flat... just like the earth.
-
I've decked a bunch of the IDI heads on a mill with the pre cups installed, just go super slow, and this was a big mill (40taper) I probably wouldn't try it with the pre cups in on a mill with like an R8 spindle or something smaller like that. I believe I was removing about 5-6 thou.
-
Dave, I sent you an email about heads. I don't know if you got it or not but I want to know if you have any 1.6 TD hydraulic heads and how much does one cost?
-
Yeah I got your email, sorry just haven't had time to reply, but at the moment we aren't offering rebuilt heads, only head porting, hopefully by the end of the summer we will have all the necessary equipment to fully rebuild heads in house. Thanks for the interest anyhow though.
-
When they alignbore they remove a bit of material from the top cap and the bottom cap... making the hole smaller. They then bore a new hole the right size all the way thru.
So, if your cam bearing caps have too much clearance this may be an option.
So doesn't this bring the camshaft down closer to the followers making the valves open farther and possibly hitting the piston?
-
I have hydraulic followers. So the the valves will not be opened farther? They adjust themselves on the cam upstroke and keep their "setting" when the cam opens the valves? I have heard of one place that heats the head and straightens it, eliminating the need to rebore the cam bearings.
If reboring the cam bearing after milling the bottom of the head is feasible, then I may do that instead of getting a new head. Unless the head is cracked of course :x