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General Tech Machining TR3A Engine liners...

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Toshi Basha

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Hi All

I'm rebuilding a TR3A motor and my machinist says the block is untidy on top and needs to be surface ground (nb not sure this is the correct term); and to compensate, the liners might need to be adjusted to suit.

To do this, he explained that a portion of material is removed from the bottom surface of the liner's lip that the liner sits on, in the block.

1. Is my machinist correct? (I would have thought it would have been easier to machine the top surface of the liner...).

2. I have read and understand that the liners need to protrude above the block top; however, when is the measurement made? Presumably the gasket needs to be in place, but does it need to be compressed? And if it is compressed does it matter if the liner is removed for machining?


All advice is appreciated,

Brian Inwood
ps. an intruder - not a triumph owner, but 1952 Morgan +4.
 
I've never had a the top block machined and block warpage seems uncommon. If it really unfair look closely for cracks, as I'm sure your machinist has. However, if you do have this done you need to have a reference point. Carefully measure every liner height after torquing and removing the head. Pressing with the head may be unnecessary, particularly if you use the steel FO8 gaskets but if you are having problems, best to be as accurate as possible. I'd suggest working with your machinist with the block, liners and gaskets and the spec sheet in hand. Usually they are a bit low and taking a bit off the block might actually fix things without grinding the liners (never done hat either). There is a considerable range of acceptable protrusion. In the old days it was easy to get gaskets of varying thicknesses, possible but difficult t get them today. Hopefully you will not need them nor need to machine any liners.
Tom
 
Unlike motors without wet liners, the top of the block doesn't have to seal against combustion pressure, only water & oil. As noted, it usually isn't a problem. Also note that decking the block (without modifying the pistons) is going to affect compression ratio, and reduce the piston-to-head clearance.

The solid gasket under the liners doesn't seem to take a set, I've always gotten the same measurement before and after trying to compress it (with the copper gaskets). However, it is important to measure the protrusion on both sides, as I've found several motors now where the top of the liner doesn't come out parallel to the top of the block. Too low on either side will leak to leaks, as will too high.

To my way of thinking, it would be better to machine the liner seats in the block to maintain the correct protrusion. That way you (or the next owner) won't have to get the liners modified again if they get replaced again. But if you are going to machine the liners shorter, I don't see why it would make a difference whether it comes off the top or off the bottom.
 
I'm kinda with Randal on this one. I don't think it would matter which end. But I'm thinking why not take it off both ends so you have fresh machined surfaces in which to seal the figure 8 gasket and the head gasket. I wouldn't think he wouldn't be taking more the 5 thousands off the deck and then the difference can be split between both ends. Take a couple of thousandths off the bottom end then let the cylinder rest in the block and take off the appropriate amount off each cylinder top to achieve the proper height off the deck.
 
One thing does occur to me : it's obviously important to keep the seating surface and the top of the liner parallel to each other. But the bottom of the liner (where it hangs out in the crankcase) doesn't matter at all. So it might be that the factory didn't machine the bottom to be perfectly parallel with the seat and top. If not, it might be easier to mount the liner by the top (against the milling table) and machine the seat; rather than trying to measure and shim or make a fixture to mate to the seat.
 
Hi All,
I apologise for not having wrapped this up sooner. It turns out I have completely misunderstood my machinist; he is not touching the liners. What he is doing is counter-boring the holes in the block where each liner sits. This seems much more sensible and something he does regularly. So all seems in order. (Now I have a new question - I'll start a new thread...).

As always, I appreciate all comments made
Sincerely
Brian Inwood
 
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