Removal and rebuilding of a Twincam

[rgh0]

Just restarting this thread in the right section !

Having had an engine internal problem causing loss of power at my last race I decide to pull the engine to investigate. It would still run without any abnormal noises or smoke but the engine is partially seized and very hard to turn over by hand and that internal drag is clearly the cause of the loss of power. I have started this thread to record both the removal process, the rebuild and re-installation. Will post more when I get a chance. The engine came out today and tomorrow I hope to open it up to find out more.

cheers
Rohan

[rgh0]

I thought I would first step through the removal sequence I use.

Having checked that everything electrical was Ok and that the engine was definitely hard to turn decided I had to remove it.

Hoses and fan wiring disconnected and ignition coil that's mounted on the side of the radiator removed and the radiator is out. Once the radiator was out I could get a big socket and long handle on the crank pulley nut and yes it was much to hard to turn

Carbs off. Much easier with the radiator out to reach under to remove the bottom nuts

Alternator off next

Removed the oil cooler from its bracket and hung on front of engine. Easier to remove the cooler when I have the engine out and take off the oil pump

The beauty of having a two post hoist like the MaxJax is you can easily work on the top and bottom of the car and position it at a comfortable working height quickly. So now up in the air and the exhaust comes off the the headers. Removable chassis brace and roll bar also removed so out of the way for the engine removal also

Half way through the engine removal after about 3 hours ......to be continued
cheers
Rohan

[rgh0]

Continuing with the engine removal

Top heater hose removed and disconnected the LH engine mount and jacked up the engine a little so easier to get at the hex socket headed set screws holding the manifold with the ball headed hex key. All installed with nickel antisieze so they come out easily.

Manifolds removed and LH side of the engine now clear for access to the bell housing bolts for removal

OIl capillary tube and lowerheater hose removed and RH engine mount and dizzy about to be removed for clear access to bell housing bolts on this side.

Engine crane installed and connected to take the weight of the engine. Again the two post MaxJax hoist makes it easy to position the car at the right height with clear access for the engine hoist legs underneath

Almost ready to take out the engine ... about 5 hours of work so far

to be continued
cheers
Rohan

[rgh0]

Continuing with the actual engine removal now that all the external ancillaries have been disconnected and the engine mounts removed and its hanging from the hoist

First lower the engine down a little for easy access to the two top bell housing bolts that face the rear and remove those

Now lift it up as high as it will come. I have to move the wiring and fuel line out of the way to be able to lift it high enough so that when its pulled forward it clears the front cross member

Place jack under the gear box to support it and then remove the remaining 4 bell housing bolts

Pull the engine forward until it clears the bell housing and then lift it up. It takes a bit of effort to get it off the hollow dowels. Keep the engine and bell housing flange parallel as its pulled forward and up at an angle to avoid stress on the gearbox input shaft

Swing the engine over and position it on the engine stand. I can just get the engine stand close enough so that the exhaust side engine mount can be bolted to the adaptor I made for the stand

Engine is out and now ready for dismantling to find out whats wrong ... about 7 hours in total to remove

cheers
Rohan

[rgh0]

Continuing now with dismantling the engine

First drained the oil - not looking good as very black and I had just changed it before the last race meeting.

Pulled off the sandwich plate and oil cooler. Found the first thing wrong .... The blanking plate in the oil pump that closes off the filter bypass is loose. The second photo shows where it should be. It is staked in place but clearly this was insufficient and it had come free at some stage. This meant that the filter was not working and oil was bypassing it but oil was circulating OK still.

Now removing the sump bolts. I again use hex socket headed set screws to hold on the sump as easy to check tightness with the engine in place and also quick to remove with a ball headed hex key.

Removed the sump and looking inside all the shiny metal bits sitting in the bottom do not look promising ! Looks like a bearing failure

Pulled and checked the main bearings. Lots of little bits of metal in them and significant but not catastrophic bearing wear. No signs of overheating or significant damage to any of the main crank journals evident but I will have to measure it more carefully once removed.

Started checking the rod end bearings. No 4 had lots of metal in it and significant bearing wear but again no sign of overheating or catastrophic failure or significant damage to the crank journal


to be continued......
cheers
Rohan

[Elanman68]

Thanks Rohan. Saved for future reference. Hope your issue is not too serious.

[rgh0]

I continued to remove the rod end bearings and when I got to No 3 I found the cause of what had probably led to the loss of power and partial seizing of the engine and where most of the bearing metal had come from.

The rod end bearing had lost all its bearing metal and spun in the Rod, It had also moved sideways and had its sides bent over as it spun. Amazingly no significant damage or overheating evident to the crank journal or the Rod though again it will need some careful measurement. It looks like it had a good flow of oil and that I had pulled up and left the track quick enough before a total seizure. Modern synthetic oils protect engine components amazingly well even during a catastrophic failure.

My conclusion of the root cause of the failure is that the filter bypass blanking plug coming loose allowed metal particles to circulate in the engine oil without being filtered and this led to rapid bearing wear. The first bearing to fail was the No3 rod end bearing when it had enough wear to allow it to spin in the rod leading to the partial seizing of the engine but no significant engine knock as it was still being well lubricated. All the metal in the other bearings was also contributing to the partial seizure.

Now to strip the engine down fully and clean and check everything. The rods and crank may be Ok and can be reused. I have not looked at the top end, cams and followers but there will be bearing metal through all of them also and hopefully no significant damage there either.

Well an interesting few days over Easter. Back to work tomorrow. I will continue to document the rest of the strip down and assessment and rebuild as I progress it over the next weeks / months

cheers
Rohan

[pharriso]

Great news Rohan, great that you had the sense to pull over rather than battle on to the end & wreck the engine.

Please continue with your posts...

[Davidb]

Damage looks similar to the damage in my engine following the oil pick up pipe fracturing last year. In my engine #2 rod bearing failed and the rod was rendered unusable. The crank, being nitrided, survived with a quick polish. I changed every bearing in the engine though.

Rohan, is there a rule preventing you from moving the radiator forward? It makes general work on the engine so much easier and engine removal in particular.

[rgh0]

re the question
"Rohan, is there a rule preventing you from moving the radiator forward? It makes general work on the engine so much easier and engine removal in particular"


Yes the radiator surround cannot be modified which implies the radiator needs to be in the original position though that is not explicitly stated. The rules are written around having an unmodified body shell and most sports cars have the radiator mount as part of the body shell and the no change to the radiator surround is explicitly added on top of this requirement

I guess i could just move the radiator forward with no surround as the wide series 3 radiator has no surround except the body. Mine is a series 4 car but all the Australian delivered series 4s continued to use the wider series 3 radiator so I modified my car to that specification as it was originally an English delivered car to give me a bit more cooling capacity when racing on hot days here.

Pulling the radiator when needed is not much of a hassle and I like it set back in its original location from a weight balance perspective. I have OK access to most things with it in place, just hard to get a decent sized spanner onto the front pulley to turn the engine by hand so I normally put the car in gear and push it forward to nudge the engine around when setting the static time of ignition or cams with the engine in the car.

cheers
Rohan

[vstibbard]

Rohan, the race gods were looking down on you, hope the crank etc and recoverable.

Shame the new pumps etc are not made other quality standards of old. Have you considered using one of John McCoys oil pumps or the other UK race spec type (PACE I think) that are available for wet sump engines. This is prompting me to consider them for future rebuilds.

I also seem to recollect in UK there was a trend to wrap OEM oil pumps in carbon to stop bodies expanding or flexing, is this still the case over there?

Cheers

Vaughan

[rgh0]

Rohan, the race gods were looking down on you, hope the crank etc and recoverable.

Shame the new pumps etc are not made other quality standards of old. Have you considered using one of John McCoys oil pumps or the other UK race spec type (PACE I think) that are available for wet sump engines. This is prompting me to consider them for future rebuilds.

I also seem to recollect in UK there was a trend to wrap OEM oil pumps in carbon to stop bodies expanding or flexing, is this still the case over there?

Cheers

Vaughan

I think I will stick to the current high volume / high pressure standard style pump. It just appears that the staking to hold the bypass valve replacement disk in place was done poorly so it dropped out, I would certainly redo that on any new pump now to make sure its secure. I will look at tapping the hole and fitting a screw in plug if there is enough metal around it or just staking the disk in place better with some high strength bonding agent in addition to the staking, fitting an interference fit aluminium pin is another alternative and then staking that. I have a few old pump bodies I can cut up to look at the wall thicknesses in the area where a plug could be fitted.

I know cracking of the body flanges can be a problem at high revs and i had a couple of failures many years ago when first building 8500 + rpm engines. The extra mass of the longer rotor and thicker end plate on the high capacity pumps appears to contribute to that problem as I never had it when using the standard capacity pumps. I solved that by mounting the pumps without the paper gasket using anaerobic loctite gasket former to seal it and have not had any pump problems since then until now.

cheers
Rohan

[Chrispy]

Thanks for putting up your work, always interested to see

[alan.barker]

Rohan,
do you think this one big end seize would have twisted the Crankshaft
Alan

[rgh0]

Rohan,
do you think this one big end seize would have twisted the Crankshaft
Alan

The failure resulted in higher drag than normal internally in the engine and loss of power to the wheels but no total seizing or overheating of the rod or crank is apparent so I dont think the crank would have been distorted. The forged Datsun L16 cranks I use are also incredibly tough.
cheers
Rohan