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#1
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Head gasket - reuse the old head or not
I have an Isuzu inline single cam 4 banger. A head gasket replacement is
in the near future since I seem to have a bit of coolant getting into at least one cylinder. The engine has 187K on it. It has been well maintained by myself since I acquired it around 100K and runs strong with very little oil usage, and has never overheated while I have owned it. I also have a completely rebuilt cylinder head sitting around that I got for next to nothing. Should I reinstall the old head (after making sure it is straight) or go ahead and install the new one since I have it? I would think this would be an excellent opportunity to do so, but I have heard that installing a new head on an old block will give me problems with excessive blowby - but is this only if the head was milled down and I don't use a shim to restore the correct clearance/compression? Unfortunately the papers for the new head were lost so I don't know how far down it was machined. Maybe I can measure this relative to the old head somehow? |
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#2
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"Ryan Underwood" > wrote in message news > I have an Isuzu inline single cam 4 banger. A head gasket replacement is > in the near future since I seem to have a bit of coolant getting into at > least one cylinder. The engine has 187K on it. It has been well maintained > by myself since I acquired it around 100K and runs strong with very little > oil usage, and has never overheated while I have owned it. > > I also have a completely rebuilt cylinder head sitting around that I got > for next to nothing. > > Should I reinstall the old head (after making sure it is straight) or go > ahead and install the new one since I have it? I would think this would > be an excellent opportunity to do so, but I have heard that installing a > new head on an old block will give me problems with excessive blowby - > but is this only if the head was milled down and I don't use a shim to > restore the correct clearance/compression? Sort of...Sometimes when you grind the valves you increase the combustion chamber volume which offsets, to a degree, a mild truing cut on the head. You can CC the combustion chambers if you really want to know. The real situation is that if your rings are worn a bit, you might not see the effect with an older head with leaky valves, etc AS MUCH AS you may see it when you install a head that is working as it should. At 187,000 miles, I would not be surprised if blowby increased....even if you just 'sharpened' the valves and did not machine the head surface at all. |
#3
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"Ryan Underwood" > wrote in message news > I have an Isuzu inline single cam 4 banger. A head gasket replacement is > in the near future since I seem to have a bit of coolant getting into at > least one cylinder. The engine has 187K on it. It has been well maintained > by myself since I acquired it around 100K and runs strong with very little > oil usage, and has never overheated while I have owned it. > > I also have a completely rebuilt cylinder head sitting around that I got > for next to nothing. > > Should I reinstall the old head (after making sure it is straight) or go > ahead and install the new one since I have it? I would think this would > be an excellent opportunity to do so, but I have heard that installing a > new head on an old block will give me problems with excessive blowby - > but is this only if the head was milled down and I don't use a shim to > restore the correct clearance/compression? > > Unfortunately the papers for the new head were lost so I don't know how > far down it was machined. Maybe I can measure this relative to the > old head somehow? Ryan, in older engines with poorer rings as well as other components, when one did a "valve job" w/o installing new rings, it would introduce new & higher compression (and pressure on the rings) and cause blow-by and oil consumption. But with modern engines, if oil usage is not a problem now, then either re-doing your head or using a newly rebuilt newer one (which I'd do one of regardless, if I went so far as to replace a head gasket)should not cause old-timey harm, like oil usage. When I say older, I'm talking about pre-1970--times before moly rings and other improvements which increased piston seal and decreased cylinder wear. HTH & good luck. s |
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