Main/big-end bearing and thrust washer replacement on a 1974 Triumph TR

Introduction

This rather lengthy article addresses changing the main and connecting rod bearings, and thrust washers of your Triumph TR6. Consider it a minor rebuild of the bottom and of your car, and if performed with diligence every 60,000 miles on your car, or when necessitated, it will extend considerably the life expectency of this tough little motor. The instructions herein are specifically for later TR6 motors with the newer oil pump, but I am sure TR5/250 and early TR6 owners will have no problems with the slight variation in oil pumps.

 

This task was performed by yours truly, neither a an experienced mechanic nor seasoned writer, over two weekends. Both the extra length of time to complete this task (a more experienced wrencher could easily complete this on one weekend) and this long article bear testament to my inexperience. Knowing that there are others out there that may feel daunted by this task is sufficient reason for me to say "You can do it".

 

Robert Bentley's Workshop manual is a must. Much of what follows is a distillation of his great tome.

 

The whys

Wear on the thrust washers seems to be a major shortcoming of the TR6 motor, and TR6 authorities often recommend that they be replaced every 60,000 miles, lest end-play become too excessive and the washers fall into the oil pan. When this happens, irreversible damage will soon destroy the block.

 

Other drivers complain of low oil pressure. When hot, a fresh motor should show 70lbs at speed, and more than 40lbs at idle. A tired motor with worn bearings may show 40lbs at speed, and 10lbs at idle. Renewing the main and connecting rod bearings, and perhaps the oil pump, goes most of the way to giving you youthful oil pressure again.

 

The peptalk

This task is not difficult. If you can safely put a car on jackstands and know how to use a torque wrench, this job can be completed within a weekend, maybe two weekends for the mechanically challenged. Perhaps the greatest challenge for me was physical strength: At 155 lbs, I am no powerhouse, and applying 65 lbft torque in the narrow confines under a car on my back did bring a sweat to my brow. Of course, this is a "no big deal" to most of you out there.

 

I would recommend draining the oil on Friday night; this will allow the oil to drip from the engine; it is not pleasant to be working under the motor only to be dripped on from above! The oil pan can be cleaned of a horrific sludge buildup the same evening. The connecting rod bearings and thrust washers can be changed on the Saturday. The main bearings can be changed on the Sunday, all bolts carefully retorqued, oil pan reattached and oil added. You could take the car for a quiet sunset cruise Sunday evening.

 

Required

You will need to order a number of parts ahead of time. You will need to order main bearings, connecting rod bearings, thrust washers, oil pan gasket, front sealing block gaskets (2) and front sealing block wooden wedges (2). These should be available from your favorite Triumph parts warehouse. Order a few sets of the thrust washers in different oversizes; they are very inexpensive and you can always return the ones you dont use.

 

[Note: Use only Vanderval or Clevite bearings. If you use bearings by other manufacturers, expect to do this job again in less than 10,000 miles. I performed this job using Glacier bearings, and inspected them after 2,000 miles. They showed very visible signs of wear and would have had to be replaced before they reached the 5,000 mile mark. Ask the vendor what bearings they sell.]

 

You will also need Plasti-gage for measuring bearing clearances, assembly lubricant, fresh oil and oil filter. This is available from any auto store.

 

If your problem is low oil pressure, you might like to consider replacing the oil pump. Kas Kastner suggests replacing the oil pump with the pump from later TR6's, because of its higher capacity and lighter weight. See Step #6 below for details on checking pump wear.

 

All the other requirements you will likely have in your garage: clean well-lit workspace, light for under the car, good jackstands, good 3/8" socket set, extension bars and torque wrench, dial gauge (borrow, dont buy), hand cleaner, shop towels, etc. For guys like me not blessed with gorilla-like strength, a 1/2" torque wrench will make life easier :)

 

I placed a sheet of particleboard under the motor to catch any wayward drips of oil. This will cramp the style of those with creepers, but concrete can be pretty cool and hard for those of us without creeper luxuries. Further, the particle boaed soaked up the wayward drips from the gaping yaw of the block.

 

And a few final words before the details. CLEANLINESS is absolutely critical. Do not allow any contamination of the crank or bearings. I kept a roll of shop towels under the car with me and cleaned my hands and tools at regular intervals. This is major surgery on your pride and joy, so keep everything clean. And do not allow ANYTHING to scratch or mar the bearing surfaces of the crankshaft.

 

Details

1. Place the car on jackstands. This is the most crucial part of the operation so make sure your car is solid before getting under the vehicle. The jackstands will have to be located behind the clutch to give you some elbow room when under the car. Chock the rear wheels and use the handbrake. Do not put the car in gear (this will be clearer later). Attempt to push the car off the stands by pushing hard from the side, front and rear. I live in California, and if there is an earthquake while I am under the car, I want all the time I can to get out from underneath! I dont like ramps very much, and the super safety conscious may want to put some spare wheels/tyres under the car for extra security.

 

2. Isolate the battery

 

3. Remove the spark plugs. This will make it easier to turn over the engine. Attach a spanner to the crankshaft extension so you can turn the motor by hand. Alternatively, you can fit a remote starter, but make sure the car is out of gear and turn the motor over using the starter before climbing under the car! As a matter of safety, do this every time if you have taken even a small break from working underneath the car.

 

4. Remove the drain plug and drain the oil from the sump.

 

5. Remove the 23 bolts and spring washers and withdraw the sump. Note that the rear-most 4 bolts are longer than the other 19. Put the longer bolts to one side so that they are easy to find at reassembly time. Removal is straight-forward as there are no obstructions.

 

6. Remove the 3 bolts holding the oil pump to the block and remove the pump. If the car is an early TR6, you may have to remove the oil strainer from the pickup first. This is done by slackening the lock nut and unscrewing the strainer.

 

At this point, you can determine if you need a new pump. Experienced mechanics tell me that the most wear occurs across the pump body face. To measure this, us a straight-edge across the pump body face (ie, across the bottom of the pump) and measure the clearance between the straight- edge and the rotors with a feeler gauge. The maximum clearance should be less than 0.004". If it is more, replace the pump.

 

7. The connecting rod bearings are numbered 1-6, starting at the front of the engine. Starting with #6 connecting rod, turn the crankshaft until it is an accessible position. Remove the bolts securing the connecting rod cap to the connecting rod. Withdraw the cap and shell from the rod. Note the orientation of the cap, and which bolt went where, because they MUST be reassembled in the same location. I used a piece of particleboard and wrote "LEFT" and "RIGHT" on the board, and placed the bolts over the word that indicated whether they came from the left or right hand side of the connecting rod, and then a silouette of the cap. You may have better ways of remembering which way things go.

 

8. Remove the lower bearing from the cap. Push the connecting rod and piston up the bore 1/2" or so to enable the upper bearing shell to be removed. Remove the bearing shell by carefully placing a small blunt screwdriver under the anti-spin tag and lift. Be very careful not to scratch the crankshaft!

 

If you can see copper exposed on the bearing surface, the bearings are pretty worn. Donate them to the nearest MGB club.

 

9. Using assembly lubricant, fit the upper bearing to the connecting rod and mount some Plasti-gage to the lower bearing when inserting it into the rod cap. Make sure the small tags are correctly aligned into their locating holes. Clean the connecting rod and cap mating surfaces and check that the dowels are in position.. The two shell bearing recesses should be on the same side. Fit the cap and torque the bolts evenly to 38-46 lbft. Remove the bolts and cap and check the Plasti-gage. The connecting rod clearance should be 0.0086-0.0125". If you are within spec, remove the Plasti-gage, reapply fresh assembly lubricant, and refit the bearing cap, torqueing to 38-46 lbft.

 

10. Repeat instructions 7-9 for rod bearing #5, then #4, etc. The reason for doing them one at a time is to minimize the possibility of mixing the caps and cap bolts.

 

The first bearing took me about 45 minutes, but as I gained experience, the later bearings took only a few minutes each.

 

11. Now for the thrust washers. These are located on either side of the main bearing at the rear of the motor, ie, main bearing #4. Remove the 2 bolts holding #4 main bearing cap and withdraw it and the lower bearing. Rotate the crankshaft and the two halves of the thrust washers will fall out. A plastic tie will help encourage them out if they seem reluctant to move.

 

There sometimes seems to be some confusion on which way to refit the washers. I found the easiest axiom to remember is that the grooved surface of the thrust washers must face

away from each other, i.e., towards the crank surface.

 

Apply assembly lube and refit the new thrust washers.

 

Using a dial guage on a magnetic base, mount the gauge to the crankcase and set the gauge stylus against the crankshaft webbing. Lever the crankshaft rearward (use a small crowbar) and zero the dial gauge. Lever the crankshaft forward (either depress the clutch or use a crowbar) and measure the end-float reading. The end-float should be 0.006-0.008". Do this a few times and average the measurements. If you have more than this, use oversize thrust washers. To obtain the required clearance, I used a combination of standard and 0.005" oversize washers.

 

 

12. Phew! So far so good. Now for the main bearings. The mains are numbered 1 through 4 from the front of the engine. I started with main #4 (already removed in step #11 above). Remove the main bearing cap with the lower shell. With the tag end leading, slide the upper bearing shell out from between the crankcase and crankshaft journal. If it does not push out easily, use a plastic tie to push it out. If still stubborn, use a feeler gauge. Note that it is VERY important not to scratch the crankshaft. If the upper bearing shell is still stubborn, loosen the cap bolts on main #3; this will allow the crankshaft to sag a little bit. It is important not to let the crank sag too long, as this may compress the main oil seals which could cause a leak. Again be careful to note which bolts went where, the the orientation of the cap, as they must be returned in exactly the same way.

 

Again, remember which main cap bolt goes where, and the orientation of the cap, as they must be refit in the same way.

 

There may be one upper shell which will refuse to come out. For these, find a nail that fits into the oil hole on the crank. Cut of the head and file the ends so that small part of the nail protrudes beyond the oil hole. Then rotate the engine by hand until the nail pushes the bearing shell out.

 

13. Using a dial gauge with a magnetic base, measure the runout on the journal; if there is more than 0.002" of runout, the crankshaft will need to be reconditioned as there is little that can be done to help it. Bummer!

 

14. Lubricate with assembly lube the new upper bearing shell and feed it with the tag end trailing between the crankcase and the journal. Ensure the tag locates correctly into the corresponding recess in the crankcase bore. Use some lube on the new lower bearing shell and fit the cap and bolts; torque evenly to 50-65 lbft.

 

15. Repeat instructions 12-14 for main #3, then main #2, etc. Again the reason is to ensure that the caps and bolts do not get mixed up.

 

Bearing #1 is perhaps the most awkward, because of the front frame cross-member. This is why I left it till last, because by now, the whole process is going smoothly. Furthermore, the front sealing block has to be removed to get at the bolts holding #1 main cap. To remove the sealing block, remove the two screws from the front mounting plate (ie timing chain cover), and also the lowest bolt from the timing chain cover. Then remove the sealing block retaining screws, and carefully remove the sealing block. You now have access to #1 main. Note the wooden wedges on either end of the sealing block. These will have to be renewed at reassembly time.

 

Refitting the sealing block after installing new bearings on #1 main is the reverse of the above instructions. Clean the mating surfaces of old gasket material, fit the new gaskets and the sealing block. Smear the wooden wedges with Permatex sealing compound and drive them in with a light mallet. Trim any excess wood so that they are flush with the sealing block, but do not undercut them.

 

I replaced the screws holding the sealing block to the front mounting plate just because it was easier for me to fit the bolts.

 

16. Fill the oil pump with oil then refit the oil pump by reversing the instructions in step #6. Filling

the oil pump with oil now helps the priming process when first starting the motor.

 

17. Retorque all bolts.

 

18. Refit the oil pan. Before doing this, it is wise to clean the pan. The gunk in the bottom will suprize you! You may also want to "flatten" the lip of the sump. Clean the mating surface thoroughly, as well as the bolt holes. Also use a new gasket. After cleaning the gasket surface, I sprayed the gasket liberally with silicon spray, and sparingly used RTV Permatex gasket sealer. It was hard work to remove the old gasket from the block; the silicon spray and Permatex make it easier the next time I have to do it, as well as making the seal more oil tight.

 

Dont forget the longest 4 bolts mount at the rear of the pan. Torque the bolts to 15-20 lbft.

 

19. Fit a new oil filter and fill with 10.8 US pints (5.10 litres) of your favorite oil.

 

20. Reconnect the battery and crank the motor until you see oil pressure on the oil pressure gauge. This will take less than 60 seconds of cranking. With the spark plugs removed, it is almost no effort for the battery.

 

21. Check the oil level again and refit the spark plugs.

 

22. Check that there are no tools under the car. Lower the car off the jackstands, and take your pride and joy for a drive. For the first 100 miles or so, pretend that you are running in a new car; do not lug the motor, do not rev it hard, vary the rpm.

 

Well, thats it. The task is easier than my description makes out. I had a tremendous sense of satisfaction at the end, and seeing my hot oil pressure at 75lbs at speed and 40lbs at idle.

 

Good luck!

Last update: 26 August 2002.