Before taking a newly acquired snowcat out for testing, or usage, it makes sense to go over it with a fine-tooth comb. If there are issues, better to discover them while you have access to all your tools and parts are somewhat accessible, and get those issues resolved; rather than suffer a break-down in the back country. Such is the case with the 1986 1544 I bought early last fall. In addition to the frame damage from water intrusion I previously highlighted, we found two of the three battery bracket mounts broken (not all that uncommon), and some broken exhaust manifold bolts. This post will discuss those.
There were four missing “bolt" heads, indicative of the bolts themselves being broken, and of course they involved both cylinder heads. Scott and I decided to try and remove them with "easy outs”, the first step being drilling a hole right down the center of the broken bolt. But... disaster... as coolant streamed out the drilled hole! And the same thing happened with the other he drilled (Expletive deleted). At that point the smart thing to do was to remove the heads and take them to an automotive machine shop for repair; which is exactly what we did.
This Tucker has the optional 360 CID Industrial, rather than the more common 318 engine, but both are in the same Chrysler “LA" engine family. This would imply 318 cylinder heads are similar. The exhaust manifolds are secured to the cylinder heads with six fasteners. It turns out the two outside exhaust manifold fasteners on each head are actually studs, and when you remove an exhaust manifold you remove the nut and washer, but leave the stud threaded into the head. Three of the four studs were broken and Scott had drilled two of these This is where the coolant came running out.
At the machine shop, Jack (the owner) told Scott they were “wet” heads, meaning the threaded holes for the studs went all the way into the water jackets, the studs prevented coolant from leaking out (as would happen when bolts were removed) and Scott had not done any damage after all. (I won’t comment on the Chrysler’s so-called "engineering".) Scott had really felt badly after the coolant came out the drilled holes - so now he was much relieved. But that wasn’t the only problem. While our intention was just to get the broken stud/bolt issue fixed, it was prudent to have the heads inspected to see if anything else needed attention. And sure enough, almost all of the exhaust valves were sunk deep into their respective cylinder heads which meant exhaust valve seat problems.
I think a little history might be helpful for the younger members of the forum. "Back in the day” gasoline was blended with tetraethyl lead. This was done as an inexpensive way of boosting octane to prevent engine knock. It was also beneficial for the exhaust valves and valve seats... preventing excessive wear, but there were negative effects in terms of pollution. The government mandated automotive pollution controls resulted in catalytic converters being added to vehicles and they required unleaded fuel. But with the change to unleaded gas, auto manufacturers started using hardened exhaust valve seats (and later different exhaust valve materials), as they found using unleaded fuel without hardened seats caused damage to the seats. My understanding is initially the "hardened seats" were merely adding the processes of either flame hardening or induction hardening to the exhaust valve seat area. That process hardens the surface, but the hardening is not very deep. For many years gasoline was sold as “Regular”, which was leaded, “Unleaded” and “Premium”. That way older vehicles could use regular fuel and not be at risk for valve seat damage. (Incidentally AVGAS (aviation gasoline) still contains lead, and is higher octane…no crappy ethanol, either!)
One would have thought that a 1986 Tucker, with presumably a 1986 engine, would have hardened exhaust valve seats. And perhaps they are, but running an engine hard for an extended period of time, such as heavy towing or use in an RV, or in a snowcat where the engine works hard almost all the time, puts added heat into the mix and more stress on the exhaust valves and seats.
When the valve seat issue was being discussed at the machine shop, it was pointed out that as the seat sinks deeper into the head, this also brings the end of the valve stem closer to the rocker arm. Eventually, it’s possible for the wear to be such that the exhaust valves don’t close properly, resulting in lousy engine performance. The process of repairing our heads will involve machining the exhaust valve seats for the installation of new seats, which are inserts that are installed and then machined. A benefit of adding hardened seats to a cylinder head without hardened seats, or one with induction or flame hardened seats, is that better materials other than the cylinder head casting material itself can be used.
This Tucker has almost exactly 1,000 hours, which is relatively low. Quite a number of Tuckers are pre-unleaded gasoline vintage, and I’m wondering how many other Tuckers (or snowcats made by other manufacturers) may have this issue. I suspect machines with a history of harder usage, such as grooming, are more prone to this condition.
A commonly expressed opinion on these forums is “This thread is worthless without pictures…” so, here you go. The first photo is of an exhaust valve and how far sunken it is. Note: the combustion chambers were thoroughly wire brushed in preparation for magna fluxing the heads to check for cracks.
An obvious question is “How can I tell if my engine has this issue without removing the cylinder heads”? The answer is to remove the valve covers and rocker arms, and then place a straightedge along the tops of the valve stems. They should all be pretty close in height, and if the exhaust valves are significantly higher, that would indicate a problem. Here’s what I’m talking about. Ruh Roh… Not good!
There were four missing “bolt" heads, indicative of the bolts themselves being broken, and of course they involved both cylinder heads. Scott and I decided to try and remove them with "easy outs”, the first step being drilling a hole right down the center of the broken bolt. But... disaster... as coolant streamed out the drilled hole! And the same thing happened with the other he drilled (Expletive deleted). At that point the smart thing to do was to remove the heads and take them to an automotive machine shop for repair; which is exactly what we did.
This Tucker has the optional 360 CID Industrial, rather than the more common 318 engine, but both are in the same Chrysler “LA" engine family. This would imply 318 cylinder heads are similar. The exhaust manifolds are secured to the cylinder heads with six fasteners. It turns out the two outside exhaust manifold fasteners on each head are actually studs, and when you remove an exhaust manifold you remove the nut and washer, but leave the stud threaded into the head. Three of the four studs were broken and Scott had drilled two of these This is where the coolant came running out.
At the machine shop, Jack (the owner) told Scott they were “wet” heads, meaning the threaded holes for the studs went all the way into the water jackets, the studs prevented coolant from leaking out (as would happen when bolts were removed) and Scott had not done any damage after all. (I won’t comment on the Chrysler’s so-called "engineering".) Scott had really felt badly after the coolant came out the drilled holes - so now he was much relieved. But that wasn’t the only problem. While our intention was just to get the broken stud/bolt issue fixed, it was prudent to have the heads inspected to see if anything else needed attention. And sure enough, almost all of the exhaust valves were sunk deep into their respective cylinder heads which meant exhaust valve seat problems.
I think a little history might be helpful for the younger members of the forum. "Back in the day” gasoline was blended with tetraethyl lead. This was done as an inexpensive way of boosting octane to prevent engine knock. It was also beneficial for the exhaust valves and valve seats... preventing excessive wear, but there were negative effects in terms of pollution. The government mandated automotive pollution controls resulted in catalytic converters being added to vehicles and they required unleaded fuel. But with the change to unleaded gas, auto manufacturers started using hardened exhaust valve seats (and later different exhaust valve materials), as they found using unleaded fuel without hardened seats caused damage to the seats. My understanding is initially the "hardened seats" were merely adding the processes of either flame hardening or induction hardening to the exhaust valve seat area. That process hardens the surface, but the hardening is not very deep. For many years gasoline was sold as “Regular”, which was leaded, “Unleaded” and “Premium”. That way older vehicles could use regular fuel and not be at risk for valve seat damage. (Incidentally AVGAS (aviation gasoline) still contains lead, and is higher octane…no crappy ethanol, either!)
One would have thought that a 1986 Tucker, with presumably a 1986 engine, would have hardened exhaust valve seats. And perhaps they are, but running an engine hard for an extended period of time, such as heavy towing or use in an RV, or in a snowcat where the engine works hard almost all the time, puts added heat into the mix and more stress on the exhaust valves and seats.
When the valve seat issue was being discussed at the machine shop, it was pointed out that as the seat sinks deeper into the head, this also brings the end of the valve stem closer to the rocker arm. Eventually, it’s possible for the wear to be such that the exhaust valves don’t close properly, resulting in lousy engine performance. The process of repairing our heads will involve machining the exhaust valve seats for the installation of new seats, which are inserts that are installed and then machined. A benefit of adding hardened seats to a cylinder head without hardened seats, or one with induction or flame hardened seats, is that better materials other than the cylinder head casting material itself can be used.
This Tucker has almost exactly 1,000 hours, which is relatively low. Quite a number of Tuckers are pre-unleaded gasoline vintage, and I’m wondering how many other Tuckers (or snowcats made by other manufacturers) may have this issue. I suspect machines with a history of harder usage, such as grooming, are more prone to this condition.
A commonly expressed opinion on these forums is “This thread is worthless without pictures…” so, here you go. The first photo is of an exhaust valve and how far sunken it is. Note: the combustion chambers were thoroughly wire brushed in preparation for magna fluxing the heads to check for cracks.
An obvious question is “How can I tell if my engine has this issue without removing the cylinder heads”? The answer is to remove the valve covers and rocker arms, and then place a straightedge along the tops of the valve stems. They should all be pretty close in height, and if the exhaust valves are significantly higher, that would indicate a problem. Here’s what I’m talking about. Ruh Roh… Not good!