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LB361 LPG / NH 3 Compressor. This presentation is a simplified description of the disassembly of a Blackmer LB361. The subsequent model, LB361A, is similar but has an O-ring instead of a flat gasket between the head and cylinder.

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lb361 lpg nh 3 compressor
LB361 LPG / NH3 Compressor

This presentation is a simplified description of the disassembly of a Blackmer LB361. The subsequent model, LB361A, is similar but has an O-ring instead of a flat gasket between the head and cylinder.

The current production model is the LB361B (August 1997). The largest difference affecting disassembly is in the oil pump. The current oil pump is self reversing and is not shown in this presentation

Select one of the following:

Hilites Only

Detailed Text

lb361 lpg nh 3 compressor2
LB361 LPG / NH3 Compressor

The LB361 compressor is suitable for many applications, but the most common is the transfer and vapor recovery of liquefied gases such as propane, butane, and anhydrous ammonia. The non-lubricated cylinder design of the LB361 allows the transfer of these products without contamination of the products and is capable of transferring up to 200 gallons per minute (760 lpm). Typically the LB361 is driven by a 10 or 15 HP driver in the 650 to 800 rpm range.


Be sure you have the proper literature before starting work on the compressor. Locate the parts list and Installation, Operation and Maintenance instructions. In addition, you may have received additional instruction sheets with your machine that further describe such items as valves and packing.

Literature is available on the web at:

or from your Blackmer distributor.


The tools normally required for small machine service will be adequate. A small strap wrench is useful as well as a good spanner. The Blackmer spanner p/n 790316 has 1/4” pins and is used for piston removal. A flat scraper and inside snap ring pliers are also needed.

Blackmer offers a complete tool kit which has all of the hand tools necessary to dismantle the machine.

On larger machines a small hoist might be needed for one man to do the job, depending on the environment. Generally, two men can handle the disassembly of any Blackmer machine.


On the side of every Blackmer compressor is a nameplate which doubles as an access opening for inspecting the piston rod.

The nameplate will show the compressor’s model number, serial number, ID number, and oil capacity.

The compressor ID is a coded number that fully describes the compressor’s construction.

Make certain that you have these identifying numbers when you call your Blackmer distributor for parts or service assistance.

lb361 compressor
LB361 Compressor

Blackmer offers a variety of LPG transfer compressors.

The LB362 is similar to the LB361 shown in this presentation but has two seals separated by a distance piece on each piston rod.

Smaller models:

LB161 / LB162 [7.5 bhp (5.5 kw)]

Larger models:

LB601 / LB602 [40 bhp (30 kw)]

LB942 [50 bhp (37 kw)]

pressure gauges
Pressure Gauges

Blackmer compressors are typically fitted with a pressure gauge on both the suction and discharge. The gauges are fitted with a pulsation dampener to eliminate much of the vibration of the gauge needle making it easier to read and extending the life of the pressure gauge.

Both suction and discharge pressure gauges should be installed on every compressor.

valve caps and hold down screws
Valve Caps and Hold Down Screws

Remove the valve caps to access the valves. Note the metal gasket under each cap; these should be replaced rather than reused.

After the valve caps have been removed, the valve hold down screws can be removed with a 3/8” Allen wrench. To prevent possible damage to the valves during assembly, the hold down screws must be completely removed from the valve cover plates.

valve cover plates
Valve Cover Plates


Once the valve caps and hold down screws have been removed, the cover plates can be removed. Note the the O–ring under the Cover Plate. These O-rings should be replaced, not reused any time the cover plates are removed.

During assembly, the valve cover plates must be installed first, then the hold down screws installed.


With the cover plates removed, the valve spacers, valves and gaskets may be taken out.

A liquid relief device in the suction valve post helps protect the compressor in case liquid enters the cylinder area. It consists of a ball and spring relief valve which will allow liquid to be returned to the suction piping if necessary.

The discharge valve is held in place by a solid post.

Make certain the metal valve gaskets are removed with each valve as they may be difficult to see in the head. The valve gaskets are normally aluminum and must be replaced when the valves are removed.

cylinder head
Cylinder Head

To remove the cylinder head, unbolt the two center head bolts from the top of the head and the six head bolts from the bottom of the head.

The two center head bolts on models with flat head gaskets have metal gaskets which are normally not reusable.

After the cylinder head bolts have been removed, the head may be lifted from the cylinder.

head gasket and piston nut
Head Gasket and Piston Nut

The LB361 head is sealed to the cylinder with a flat head gasket. Carefully use a flat scraper or putty knife to remove the old gasket material before installing a new one.

The LB361A and LB361B use O-rings to seal the cylinders.

The piston nut is removed with an adjustable spanner. This spanner has two 1/4” pins which fit into holes in the top of the piston nut. Note the nylon locking device on the piston nut.

piston removal
Piston Removal

Once the piston nut has been removed, the spanner is used to unscrew the piston from the rod. Under each piston is a thick washer and one, or more, shims. These shims adjust the height of the piston in the cylinder. This is referred to as the “deck height”. Unless a major part has been changed, the deck height should not need adjustment. Changing the piston, crosshead assembly, cylinder body, main bearings or crankshaft may require adjustment of the deck height.

Rotate the crankshaft to bring the other piston to top-dead-center for removal. Each piston is fitted with three piston rings. Each ring has a stainless steel expander between it and the piston. Install each piston ring with the bevel on the inside facing up. The ring and expander gaps should be staggered at 180° intervals during installation.


With the pistons removed, the cylinder can be unbolted and removed to gain access to the packing boxes. Two O-rings seal the bottom of the cylinder.

Notice the passage in the bottom of the cylinder between the bores. This allows gas to move from one cylinder to the other as the pistons move up and down.

packing box removal
Packing Box Removal

The packing boxes are secured by a hold down screw which is removed with the same adjustable spanner that was used on the piston nut and piston. Note that the hold down screw also has a nylon insert that keeps it in place.

The packing boxes may now be lifted off the rod. O-rings seal the bottom side of the packing boxes.

packing box disassembly
Packing Box disassembly

To remove the seals (packing) from the box:

Remove the top snap ring with a pair of inside snap ring pliers. Depress the spring with a screwdriver handle to make this operation easier.

rod seals
Rod Seals

With the snap ring removed, the top washer, spring, middle washer, seal rings, bottom washer and retainer ring can all be removed.

The seal consists of three types of rings. One ring is a male ring, next a series of V-rings, then a female ring.

On LB361 compressors, the spring and male ring will be at the top and the female ring will be at the bottom.

piston rod inspection
Piston Rod Inspection

The piston rods and the top on the crossheads are visible through the opening when the nameplate is removed.

The crosshead guide is secured to the crankcase by six bolts.

crankcase and crosshead
Crankcase and Crosshead

With the crosshead guide removed, the crosshead / piston rods are visible. The flat gasket on top of the crankcase may require the use of a flat scraper to remove completely.

The oil dipstick is located in the access cover. On current models, it is located adjacent to the access cover. The oil viscosity and capacity are found in the Instruction Manual.

crosshead connecting rod removal
Removal of the crankcase access cover and gasket permits access to the connecting rods. After the bottom cap of the connecting rod has been removed, the piston rod / crosshead and the top half of the connecting rod may be lifted off from above.Crosshead & Connecting Rod Removal
crosshead and connecting rod
The connecting rod and crosshead assembly are separated by removing the wrist pin in a bench press. Note that the wrist pin has a plastic retainer plug on each end.

The piston rod is permanently secured to the crosshead at the factory and no attempt should be made to separate them. Final machining is done to the assembled crosshead / rod which precludes their reassembly once separated. The grooves in the crosshead are lubrication channels.

The small end of the connecting rod has a bronze bushing and is lubricated via and internal port running the length of the connecting rod.

Crosshead and Connecting Rod
crosshead and connecting rod cont d
Crosshead and Connecting Rod (cont’d)

A precision insert split shell bearing is located at the big [journal] end. Tabs on the bearing shells fit into slots in the rod and bearing cap. These retain the shells and align the oil feed holes.

The LB361 uses a bronze bushing on a steel wrist pin at the small end of the conrod. The oil admission hole in the bearing or bushing must align with the oil supply hole in the connecting rod small end. When the bronze wrist pin bushing is replaced, it must be honed to final dimension after being pressed into the connecting rod

The rod and cap are matched sets, do not mix. Match marks must align when assembling bearing cap to connecting rod.

oil pressure adjustment strainer
The oil pressure adjustment screw includes an O-ring, lock nut, spring and ball. Turn the screw inward (clockwise) to increase the oil pressure setting.

The oil pickup tube with washers, O-ring and strainer fits in the crankcase under the bearing carrier. If any foreign material is noticed in the strainer, its source should be quickly identified to prevent reoccurrence of the problem.

The pipe plug next to the oil pickup tube opening is the crankcase oil drain.

Some units will be fitted with an external oil filter (not shown).

Oil Pressure adjustment, Strainer
oil pump
Oil Pump

This photo shows the oil pump used in the LB361 and LB361A. The LB361B uses a different pump.

Remove the oil pump cover and O-ring to withdraw the oil pump. Notice the small O-ring on the pump shaft and the bronze bushing in the bearing carrier.

The oil pump cover can be installed with either left or right rotation arrow visible. When installing the cover, make sure that the arrow at the TOP of the cover indicates the desired rotation direction.

bearing carrier
The photo shows the bearing carrier / oil pump used in the LB361 and LB361A. The LB361B uses a different style.

The entire bearing carrier / oil pump assembly, with gasket, can be removed intact. This allows the crankshaft to be removed.

Note the slot in the end of the oil pump drive shaft. This slot must align with the drive tang in the end of the crankshaft during installation.

Bearing Carrier
crankshaft removal
Remove the crosshead and connecting rod assemblies to proceed with the crankshaft removal. Notice the lubrication holes on the bearing journals. Also note the spray nozzles on the crankshaft. The spray nozzles lubricate the crosshead guide and the main [ roller ] bearings.

The top of the crankcase is fitted with a breather which prevents entry of foreign material into the crankcase but allows the release of crankcase pressure.

Crankshaft Removal
bearing cover plate
The bearing cover plate is on the flywheel side of the crankcase. Behind this plate are a series of shims which adjust the preload on the main bearings. These shims are normally reusable and the shim thickness will not have to be adjusted unless the crankshaft and / or main bearings are replaced. The bearing cover plate also contains a crankshaft oil seal.Bearing Cover Plate
end of presentation
End ofPresentation

1809 Century Avenue

Grand Rapids, MI, USA 49503

Ph: 616-241-1611

Fax: 616-241-3752

lb361 lpg nh 3 compressor4
LB361 LPG / NH3 Compressor

Liquid transfer / vapor recovery of:



anhydrous ammonia

Transfer without contamination

Up to 200 GPM

(760 lpm)

Usually driven by 10 or 15 HP driver at 650 to 800 rpm


Have the proper literature at hand

Parts lists

Installation, Operation and Maintenance manual

For literature:

Call your Blackmer distributor


Use standard tools for small machines

Blackmer adjustable spanner with 1/4” pins (p/n 790316)

Inside snap ring pliers

Blackmer tool kit available

  • Model number
  • Serial number
  • I.D. number
    • Defines construction
  • Oil capacity
  • Rod inspection access
lb361 compressor1
LB361 Compressor

Other Models Available:


[7.5 bhp (5.5 kw)]

LB362 double-seal

LB601 / LB602[40 bhp (30 kw)]

LB942 [50 bhp (37 kw)]

pressure gauges1
Pressure Gauges

Always install!

Suction & Discharge

Pulsation dampener- extends gauge life & makes it easier to read.

valve caps and hold down screws1
Valve Caps and Hold Down Screws

Cap gasket (metal)

Remove screws with 3/8” Allen wrench

Remove screw completely from cap!

valve cover plates1
Valve Cover Plates


  • O-rings under cover plates are not normally reusable
  • Install the cover plates first, then the hold down screws

Valve Spacers

Liquid relief device - ball & spring



Valve gaskets - usually aluminum

Always replace gaskets

cylinder head1
Cylinder Head

Two center head bolts have metal gaskets

(LB361 only)

Six bolts from the bottom

head gasket and piston nut1
Head Gasket and Piston Nut

Head Gasket (LB361)


(LB361A & LB361B)

Remove old gasket material!

Remove piston nut with 1/4” pin spanner

Piston nut has nylon locking insert

piston removal1
Piston Removal

Use spanner to unscrew piston

Washer and shims adjust piston deck height

Piston rings have expanders

Bevel on inside of the ring faces up

Install rings and expanders with staggered gaps


Two O-rings seal the cylinder to the crankcase

Under-piston channel between bores

packing box removal1
Packing Box Removal

Remove hold down screw with spanner

Hold down screw has nylon locking insert

O-rings seal bottom of packing box

packing box disassembly1
Packing Box disassembly

Depress spring with screwdriver

Remove retainer ring with inside snap ring pliers

rod seals1
Rod Seals

Female packing ring on bottom

“V” - ring type

Male packing ring on top

Spring is on top of the packing

piston rod inspection1
Piston Rod Inspection

Piston rods and tops of the crossheads are visible through the nameplate opening

crankcase and crossheads
Crankcase and Crossheads

Gasket between crankcase and guide

Oil level dipstick

crosshead connecting rod removal1
Access cover and gasket

Remove lower bearing caps, lift crosshead and connecting rod assembly

Crosshead & Connecting Rod Removal
crosshead and connecting rod1
Plastic retainer plugs

Connecting rod has cast-in oil channel, big end to small end

Connecting rod is Ductile Iron

Cast iron crosshead

Don’t remove piston rod from crosshead

Crosshead and Connecting Rod
crosshead and connecting rod cont d1
Crosshead and Connecting Rod (cont’d)

Wrist pin is pressed into the crosshead

Wrist pin bushing is pressed in and honed to the proper bore

Bushing oil hole must align with connecting rod feed hole

Split bearings on the crankend

Keep rod caps on the correct rod - use match marks

oil pressure adjustment strainer1
Oil pressure adjustment screw and lock nut

Clean the oil strainer

Oil drain plug

External oil filter on some units

Oil Pressure adjustment, Strainer
oil pump lb361 lb361a
Oil Pump(LB361 & LB361A)

May be installed for either rotation direction

The top arrow indicates rotation direction

Rotate cover 180° for opposite rotation direction

crankshaft removal1
Pressure lubrication holes at the journal bearings

Oil spray nozzles on the crankshaft for the crossheads

Crankcase breather vent

Crankshaft Removal
bearing cover plate1
Located at flywheel end

Shims adjust main bearing preload

Cover contains crankshaft oil seal

Bearing Cover Plate
end of presentation1
End ofPresentation

1809 Century Avenue

Grand Rapids, MI, USA 49503

Ph: 616-241-1611

Fax: 616-241-3752