Frost plug immersion heater and improved clamping structure

A frost plug immersion heater has improved clamping structure which comprises a clamp element having a base engageable against the inner end of the heater body and a pair of channel-shaped clamping arms narrower than the base extending in splayed relation from opposite sides of the base, with the free ends of the arms initially close enough together so that the heater can be installed straight into a cylinder block core plug hole. A T-shape bolt has a cross arm bar-shaped head which has opposite ends engaging in the arm channels and spreads the clamp arms when a nut threaded on the outer end portion of the bolt shank is tightened against the outer end of the heater body. The cross arm head has a thickened crown area of maximum mass providing a maximum strength portion aligned with the shank of the bolt and the top of the cross arm tapers with diminished mass toward the opposite ends thereof to provide a truss-like reinfocement for the head when force is applied through the bolt shank as the nut is tightened.

This invention relates to frost plug immersion heaters, and is more 
particularly concerned with new and useful improvements in the structure 
for securing the heaters in place in the core plug holes commonly provided 
in the cylinder blocks of liquid cooled engines. 
Electrical frost plug immersion heaters, as such, are well known. Typical 
examples of such heaters are represented in U.S. Pat. Nos., to Winslow 
3,646,314 and to Feldmann 3,766,356 and its Canadian counterpart No. 
963,518. 
A problem encountered with the arrangement disclosed in said U.S. Pat. No. 
3,646,314 is that it provides a rocking or swivel type locking device in 
order to clamp the heater within the frost plug hole of an engine block. A 
serious drawback of heaters so equipped is the difficulty involved in 
installing the same rapidly and easily, especially where the installation 
is to be effected along a continuously moving factory engine production 
line. The installing workmen have to become extremely adept at installing 
heaters so equipped to attain the speed and accuracy required for proper 
installation. The difficulty is that because the clamping bar is longer in 
overall length than the diameter of the frost plug hole, the bar must be 
tilted during installation in order to lead it into the hole. This can be 
difficult depending on casting wall thickness and internal space 
limitations within the coolant cavity in the engine block. 
A serious problem in respect to the arrangement disclosed in said U.S. Pat. 
No. 3,766,356 is that the clamping screw is necessarily threaded through 
the clamping bar, with the head of the screw at the outer side of the 
heater body. In the first place, the head of the screw is located in a 
recess in the front end of the body and is thus inconvenient for wrenching 
during installation. More disadvantageously, if the clamping bar is 
permitted to become loose relative to the spreadable clamp arms, the two 
elements can become disoriented and the installer loses control and must 
pull the plug and reorient the parts and reinstall the same. Also, should 
the screw be turned too far in the wrong direction, especially to unfasten 
the heater for replacement, the clamping bar can drop off into the engine 
block coolant cavity. If there is only a small clearance with a cylinder 
wall, the screw shank tip may be stopped before full tightening occurs. 
It is therefore an important object of the present invention to provide a 
new and improved frost plug immersion heater, and in particular structure 
for efficiently securing such a heater in place, and which will overcome 
the disadvantages, drawbacks, inefficiencies, shortcomings and problems 
inherent in prior structures. 
The invention is embodied in a frost plug immersion heater for liquid 
cooled engines and which comprises a substantially cylindrical body having 
inner and outer ends. A electrical heater element extends from said inner 
end of said body and has means at the outer end of said body for operative 
connection to a source of electrical energy. Clamping structure for 
securing said heater in a frost plug hole in an engine block wall 
comprises an elongate clamp element having a base engageable against said 
inner end of said body and a pair of clamping arms extending in splayed 
relation in alignment with each other bendably from opposite sides of said 
base. The free ends of said arms initially are spaced apart no greater 
than the diameter of said body but the overall length of said element 
including said base and said arms is substantially greater than the 
diameter of said body. A substantially T-shaped bolt has a central shank 
extending through aligned clearance holes extending through said base and 
said body, so that a threaded outer end portion of said shank extends from 
the outer end of said body and a cross arm head rigid on the inner end of 
said shank engages at its opposite ends with inwardly facing diagonal 
surfaces of said arms. A nut is threaded on said threaded outer end 
portion of said shank and thrustingly opposes said outer end of said body. 
Thereby said body with said clamp element and said bolt assembled 
therewith can be inserted straight into said frost plug hole until a 
lateral flange on said body engages an outer side of the engine block wall 
about said frost plug hole, and then by tightening said nut said cross arm 
head is drawn toward said inner end of said said body and causes said arms 
to bend toward said inner end of said body and thereby into engagement 
with an inner side of said block wall about said frost plug opening to 
clampingly secure said body in said frost plug opening. The base of the 
clamp element is of substantially uniform width entirely about the bolt 
shank clearance hole which extends through the base. The arms of the clamp 
element are of substantially rigid channel shape, substantially narrower 
than the base and have longitudinally extending spaced side flanges which 
project generally inwardly. The cross arm head of the bolt is of generally 
elongate bar shape and fits between the flanges in the channels of the 
arms. 
Among advantages of the invention are that the heater is adapted to be 
installed easily by simply inserting it by straight line inward movement 
into position in the selected frost plug hole of an engine block, and then 
by tightening the nut on the clamping bolt securing of the heater is 
completed. The simple two stage rapid installation of the heater thus 
permits relatively inexperienced installing personnel to effect 
installation rapidly and efficiently.

A frost plug immersion heater 10 embodying the present invention comprises 
a disk-like cylindrical body 11 of a diameter to be received slideably in 
a frost plug hole 12 (FIG. 1) in a wall 13 of a liquid cooled engine 
block. On its outer end, the body 11 has an annular lateral seating flange 
14 which engages the outer face of the wall 13 about the opening 12. 
Adjacent to its inner end, the body 11 carries a sealing O-ring 15 mounted 
in an annular groove 17 and engaging the wall defining the opening 12 to 
seal the joint between the body 11 and the wall of the opening against 
leakage pass the heater body. Projecting inwardly from the body 11 in 
customary manner is a heater element 18 having prong means 19 at the outer 
end of the heater body 11, and more particularly an outwardly projecting 
boss 20 on the body, for connection with an electrical energy source. 
New and improved, economical, simple, efficient clamp structure 21 is 
provided for securing the heater 10 fixedly in place after installation of 
the heater in the frost plug hole 12. In a preferred construction, the 
structure 21 comprises a clamp element 22 and a T-bolt 23. The clamp 
element 22 may be fabricated as a die stamped metal or spring part. The 
bolt 23 may comprise a mild steel forging. 
As fabricated, the clamp element 22 comprises a base 24 of substantial area 
adapted to lie flat against the inner end of the heater body 11. A central 
bolt hole 25 through the base 24 is in assembly aligned with a matching 
bolt hole 27 through the heater body 11. Projecting in alignment from 
respective opposite sides of the base 24 are clamp arms 28 which join the 
base 24 along respective bend junctures 29. As fabricated, the arms 28 
extend in splayed relation from the base 24 and have their free ends 
spaced apart no greater than the diameter of the heater body 11. Each of 
the arms 28 has along each opposite side a reinforcing flange 30 
projecting generally inwardly, whereby each of the arms is of 
substantially channel-shaped cross section with an inner surface 31 
extending diagonally relative to the base 24. It should be noted that the 
base 30 is of substantially uniform width, in a preferably circular form, 
entirely about the bolt hole 25 and is substantially wider across the axis 
of the element 22 than the width of the arms 28. Thereby the bolt hole can 
be of generous diameter to accommodate a bolt shank of maximum diameter 
for the present purpose, and without sacrificing strength in the base area 
to resist efficiently bending stresses that may be imposed in the surface 
for which the clamp structure 21 is intended. Nevertheless, the side 
flange-reinforced arms of the element are adapted to be of as narrower 
width as practicable, and as shown, substantially narrower than the base 
24. This promotes maximum efficiency in use of material, enabling the 
clamp element 22 to be formed from minimum material without sacrificing 
overall effectiveness of the part. In fact, it will be apparent that even 
though the base 24 is wider than the arms 28, no additional material is 
required for such width, since the width of the original blank from which 
the element 22 is formed must be at least as wide as the base 24 to 
provide material for the flanges 30 to be formed therefrom up along the 
sides of the inner surface 31 of the channel-shaped cross-section of the 
arms. 
The T-bolt 23 has a central shank 32 of sufficient length to extend through 
and beyond the aligned bolt holes 25 and 27 in assembly and with a 
threaded outer end portion 33 of the shank extending from the outer end of 
the body 11. An elongate bar-like cross arm head 34 rigid on the inner end 
of the shank 32 is located to engage at its opposite ends with the 
inwardly facing diagonal surfaces 31 of the clamp element arms 28. In the 
preferred construction, the head 34 is of a width to engage freely within 
the channels between the side flanges 30 of the arms 28. In length, the 
head 34 is dimensioned to engage the splayed clamp arms 28 well beyond the 
bend junctures 29, desirably above the longitudinal midpoint of each of 
the arms so that by drawing the head 34 toward the clamp arms 28 efficient 
bending leverage will be applied to spread the arms apart. For maximum 
strength with minimum material, the bolt head 34 has its maximum mass in 
its crown portion 35 aligned with the integral shank 32. From the center 
of the crown 35, the top of the bolt tapers with diminished mass toward 
each opposite end providing truss-like reinforcement advantage for the 
head when force is applied through the shank 32. To facilitate application 
of force by the head 34 against the diagonal surfaces 31 of the arms 28, 
the contact or thrust ends of the head 34 are desirably chamfered or 
rounded to provide thrust cam surface 37 (FIG. 6). 
In the assembly, after the clamp element 22 and the bolt 23 have been 
assembled together and the shank 32 extended through the bolt hole 27, a 
sealing washer 38 is applied about the bolt shank 32 and a nut 39 threaded 
onto the threaded portion 33. The heater 10 as a complete assembly is then 
ready to be installed in the frost plug hole 12. This can be effected by a 
quick inward maneuver in which the heating element 18 is directed into and 
through the hole 12 and the heater then pushed straight inwardly into 
place without any regard to the clamping structure 21 until the stop 
flange 14 engages with the block wall 13, whereupon the readily accessible 
nut 39 is tightened, causing the sealing washer 38 to thrust sealingly 
against the outer end of the boss 20 about the outer end of the bolt 
clearance bore 27. As the nut 39 is progressively tightened, the cam ends 
37 of the bolt cross arm head 34 thrust camingly against the surfaces 31 
of the clamp arms 38, causing them to bend about the bend junctures 29 
toward and into engagement with the inner side of the engine block wall 
about the frost plug opening to clampingly secure the body in the frost 
plug opening 12. To enhance the grip of the free end portions of the arms 
28 with the wall 13, central gripper prong terminal projections 40 are 
desirably formed on the arm ends. It will be appreciated, of course, that 
the overall length of the clamp element 22 should be calculated to bridge 
entirely across the frost plug hole 12 for which the heater 10 is designed 
and sufficiently laterally beyond the sides of the hole when the clamp 
element is spread out from its initial generally V-shape configuration to 
attain a thorough clamping grip with the wall 13 under the draw-up 
pressure exerted by the bolt head 34. 
It will be understood that variations and modifications may be effected 
without departing from the spirit and scope of the novel concepts of this 
invention.