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Tucker Cylinder Head "Surprise"...

Blackfoot Tucker

Well-known member
GOLD Site Supporter
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.

IMG_1990.jpg

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!

IMG_1986.jpg
 

PJL

Well-known member
Well it is good fortune you pulled the heads off. Burned exhaust valves in the back country is not fun.
 

bobby wilkes

New member
Edelbrock makes awesome aluminum ones with pressed in stellite seats. the heads are Lighter and dissipate heat better! you can normally run 1 pointer higher compression with aluminum! But lighter is better in the snow cat world Just sayen:unsure:
 

mla2ofus

Well-known member
GOLD Site Supporter
Since you'll need a valve job, get the valve guides knurlized. Helps lubricate the valve stems.
Mike
 

The Sweet Wbj1

Active member
My vote is another engine swap! Thundercat Jr! Maybe a nice 6.2 LS. If it winds up being difficult to sell you can just add it to the collection!!!
 

Blackfoot Tucker

Well-known member
GOLD Site Supporter
Edelbrock makes awesome aluminum ones with pressed in stellite seats. the heads are Lighter and dissipate heat better! you can normally run 1 pointer higher compression with aluminum! But lighter is better in the snow cat world Just sayen:unsure:


I mentioned the valve seat situation to my machinist friend in Vermont and he suggested exactly what you did! You're in good company...



The cost to repair the stock heads is estimated at $500. The Edelbrock heads at Summit Racing cost $718.40...EACH. The plan at this point is to sell this Tucker when we've made all the repairs, given it a complete service, and made a few modifications. So a big part of the decision process is what is a potential buyer willing to pay for? When it comes to performance aftermarket cylinder heads...I'm not sure, but I have my doubts.
 

Blackfoot Tucker

Well-known member
GOLD Site Supporter
My vote is another engine swap! Thundercat Jr! Maybe a nice 6.2 LS. If it winds up being difficult to sell you can just add it to the collection!!!

If I was going to keep this machine; absolutely. But an engine swap to an LS series engine is expensive and there's a ton of labor involved. Just as I mentioned above, the question becomes what modifications can you do, and get your money out of them? I haven't added up all the costs of the engine and transmission swap we did with Thundercat; because it's a number I don't want to know. But I can say unequivocally - it was a chunk.

This Tucker already has an automatic, but a nice 6.2 with all the required parts for the conversion could easily top $5K. And it's a lot of work. When people think of swapping in a different engine, they often think of the mounts necessary for the engine (and transmission, if that's going to be changed). But that's really just the tip of the iceberg. In many automotive swaps you can literally buy all the parts you need from various aftermarket suppliers. But no one that I know of sells those similar parts for Tuckers, which means lots of time doing research, then design and fabrication.

For example, one such hurdle to overcome is the Tucker's Vickers hydraulic pump. You have to mount the pump to the engine, and drive that pump. This is what we went through with Thundercat:

The top photo is the stock Tucker hydraulic pump with the dual V-groove pulley. Note that it has a split-collar that attaches it to the pump’s shaft. From memory, that pulley is 8” in diameter and the drive pulley on the 318's harmonic balancer is 6”. So you would say the hydraulic pump is “under-driven”, meaning it spins slower than the engine by the 8/6 ratio. The engine turns 1.33 revolutions for each pump RPM.

DSC00937.jpg

Here's a photo of the harmonic balancer on the 8.1. Note that it has two sets of multiple, small narrow grooves. Those are for two serpentine belts; the inner set for the water pump, alternator and power steering pump and the outer set for the air conditioning compressor. The diameter is 7.3 inches. Maintaining the same drive to driven pulley ratio would mean a pulley on the hydraulic pump that's 9.7 inches. That's Huge!

DSC01907.jpg

Now comes the research: Chevrolet put the 8.1 in various pickup trucks, Suburbans and the Avalanche, but they also installed it in medium-duty trucks, and it was sold as an industrial engine and as a marine engine as well. Research revealed they used a different harmonic balancer in the marine engine application. That balancer was also machined to accept a bolt-on auxiliary pulley.

So I purchased a new marine type balancer and then contacted MerCruiser to get the diameter of the auxiliary pulley they use to drive the seawater pickup pump. Their so-called "customer service department" was no help whatsoever, but I took a chance and ordered one anyway. The diameter of that was 4 1/2" which enabled us to use a much smaller pulley on the hydraulic pump. Here's a photo of the harmonic balancers. Left is stock automotive 8.1. On the right is the new balancer I bought (hard to find, BTW) and the MerCruiser auxiliary pulley that bolts in front.

DSC01912.jpg

My machinist friend in Vermont drew up a new pulley for the hydraulic pump and we had one custom made from aluminum and then hard anodized. But that pulley mounts differently, which required a different shaft in the hydraulic pump, so that had to be purchased, the pump disassembled and the new shaft installed.

So now we had the problem of driving the pump resolved, but still had to mount it. Scott and I spent a considerable amount of time designing and then refining the design, with gussets for added strength and rigidity. By the time we were done cutting and welding I think there are 11 different pieces of steel plate involved and it weighs something like seven pounds. But it is very solid (yes, it's over-built). We used the same tensioner that the a/c compressor used on the stock 8.1. Hours of research, probably $450 in parts, not including a nickel for labor, and this is just one relatively small aspect of the swap...

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