Lotus Elan

Removal and rebuilding of a Twincam

PostPost by: rgh0 » Sat Apr 25, 2020 7:10 am

Now to continue with the dismantling of the block components.

Removed rear crank oil seal carrier

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Removal of engine seal. The engine was sealed by attaching a numbered seal through a couple of the bolts on the front cover. This was done by the class eligibility officer when it was built after measuring bore and stroke before the head went on to verify it complies with the rules. I will need to get it resealed once I rebuild the bottom end to this point.

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Removed the alternator brackets including triangular reinforcing bracket for where top connection mounts on the front cover. Even with this bracket you can get cracking in the front cover around where the top arm is mounted due to vibration in the nose of the engine at 8500 rpm+

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Front cover unbolted and removed from back plate.

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Jack shaft sprocket bolt locking tabs bent down and sprocket removed showing the adapter on the end of the jack shaft. Note I have turned down the heads of these bolts for clearance on the front cover as standard height bolts hit the cover

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central bolt on back plate removed so the back plate itself can be removed. Paper gasket between block and backplate sealed using Loctite Aviation Gasket cement as was done with the other cork and paper gaskets. As well as sealing well I find this releases the gaskets with minimum effort for easy cleanup

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jack shaft, crank and pistons / rods removal coming up next.... I hope I have not bored you to much so far :lol:
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PostPost by: rgh0 » Sat Apr 25, 2020 7:46 am

Continuing with the rest of the block dismantling


Jack shaft adaptor removed, flatten locking tabs and remove bolts holding jack shaft locating thrust plate.

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Removed Jack shaft. This is a short steel shaft with no cam lobes and the BDA style single lubrication slot and groove to feed oil to the cam bearings

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Big end caps removed and pistons and rods tapped out the top of the block. Forged lightweight JE pistons and Carrillo rods.

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On closer examination the rod big end on No3 piston where the bearing spun is showing signs of a little overheating. See the blueing of the No3 rod near where the rod shank joins the big end compared to the No4 rod next to it. Looks like at least 1 new rod as I would not risk that rod in a race engine . I will check its dimensions and hardness and if OK I may use in a future road engine but in a race engine I would definitely worry even if it tested out OK.

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Main bearing caps removed and crank out. Journals look OK except for No3 which will definitely need at least a polish. The crank and rods will be more closely inspected and measured to determine what needs to be done before rebuilding the engine.

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Some damage to the thrust bearings. The clutch (rear) side one has overheated by the look of it maybe due to metal in the oil but also maybe due to sitting on the line at 5000 rpm with the clutch in waiting for the red lights to go out. I have not seen this damage before in my race engines. The front thrust bearing is an over thickness one made to provide the correct clearance with the Datsun L16 crank whose thrust faces are slightly wider apart than the standard ford crank

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The block bores look good. The polishing of the hone on the thrust face area can be seen in the photo but the home marks can still be seen is this area and more clearly in the rest of the bore. Will carefully check the bore and pistons to ensure they can be reused. This block and piston and crank set has been used 2 times now in race engine builds without re-machining and with any luck they will be good for another rebuild

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to be continued...
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PostPost by: rgh0 » Sat Apr 25, 2020 8:09 am

Well this has finished the dismantling and next steps are cleaning and close inspection and measurement of all components to generate a list of what parts and machine shop work are needed before reassembly.

So far its at least

Polish No 3 conrod crank journal
Replace No 4 inlet valve follower sleeve.
Replace No 3 Carillo rod.
New set of ARP rod bolts ( I always routinely replace them )
A complete new set of bearings including clutch thrust and pilot bearing ( i have)
A new engine gasket set ( I have)
Debating in my head whether I do a routine water pump rebuild as its only 3 years since it was done and it all appears OK.

This is my engine block number RH4. I stamp all the blocks that have passed through my hands on the front face so I can keep track of them.

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Now is this a "crate engine" as those in the USA would say or is it an engine in a crate :lol:

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The cleaning and checking and measuring I will get done in the next couple of weekends. I need to decide whether I rebuild this engine or convert another spare race engine I have to a lower compression ratio to 11:1 to suit 98 Octane unleaded to put back in the car. This spare engine was built with a 12.5 compression ratio for Avgas and it came out of the car 3 years ago when the rules changed banning leaded fuels in historic racing in Australia and the engine that I just dismantled went in.

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PostPost by: 69S4 » Sat Apr 25, 2020 9:55 am

Are machine shops doing the sort of work you'll need still open at the moment? I've got some motorcycle parts in for repair work caught up in the lockdown here for six weeks now as the business owner has laid off all his staff and shut down his sales counter. He's doing what he can on his own but everything is backed up. What should have been 10 days is now going to be at least two months.
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PostPost by: rgh0 » Sat Apr 25, 2020 10:12 am

I will check next weeks if they are open. Most car repair places have stayed open as essential services here so I hope so. Getting work done appears to be quicker than normal as most people not driving plus many people out of work and cant afford repairs so the repair places are looking for work I have been getting quotes for a clutch replacement on my Landcruiser ( after 440000 kms) and people are all offering discounts and can do the job immediately

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PostPost by: HCA » Sat Apr 25, 2020 1:52 pm

Are you allowed to use the cartridge front cover modification? It must be quite costly if half way through a season a bearing decides to fail - I cannot imagine it is easy either to get a scrutineer mobilised to cover the vast distances for what might be classed as a routine repair.. :shock:
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PostPost by: joe7 » Sat Apr 25, 2020 4:20 pm

Just looking at the head it appears that #2 Ex valve is a little lighter color than the rest. Would that indicate running leaner or ?
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PostPost by: rgh0 » Sun Apr 26, 2020 4:12 am

HCA wrote:Are you allowed to use the cartridge front cover modification? It must be quite costly if half way through a season a bearing decides to fail - I cannot imagine it is easy either to get a scrutineer mobilised to cover the vast distances for what might be classed as a routine repair.. :shock:


We are allowed to modify internal engine components but must use the original block and head castings. Modification of these components by machining is permitted but not building up by welding except to repair damage. I have used removable cartridge front covers in the past and the eligibility officer has not noticed or objected and as it is a modification by machining and is principally an internal component it is technically allowable at least in my opinion :lol:

When I built this engine back in 2016 / 2017 no one had new cartridge pump front covers in stock but I was promised one in a couple of weeks so I ordered it. It did not come in the time required so I fitted a standard new one that was available within a week ex stock. The cartridge one I ordered was delivered finally about 2 months later after I had finished the engine. I will probably fit this during this rebuild.

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PostPost by: rgh0 » Sun Apr 26, 2020 4:31 am

joe7 wrote:Just looking at the head it appears that #2 Ex valve is a little lighter color than the rest. Would that indicate running leaner or ?


It may be a bit leaner. The engine has been set up to run on the rich end of tune for maximum power and minimum risk of burning valves and pistons and theoretically everything is the same in terms of chokes and jets etc so I expect a bit of carbon build up. Maybe a bit more of a carb O-ring leak on number 2 could have caused it to run fractionally leaner but the rest of the plugs, combustion chambers and piston tops even in No2 are all the same colour with the plugs a nice grey / brown tint and black carbon coated on piston tops and combustion chamber

I wiped out the combustion chambers when I removed the head to get rid of oil and water that gets in when you first lift the head off. Wiping removed the loose carbon off No 2 exhaust valve and revealed the light deposits you see underneath when it did not on the other combustion chambers. When i clean up the head I expect I will see similar light brown / grey deposits on the face of all the exhaust valves under the soft carbon coating on the surface

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PostPost by: promotor » Sun Apr 26, 2020 10:56 am

Rohan if you are looking for more lubrication at the rear thrust washer would your race series allow this small mod (I don't think it can hurt not to do it if I'm honest) to the centre main bearing housing? :

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If you are using custom made thrust washers is there no way of copper or bronze ones being made as those you have look to be silicon alloy (in colour at least)? Lead copper etc is good at accepting particles into the material and keeping it away from the metal surface it runs against. Silicon alloy seems a bit hard for this.
Could you also modify the block to accept full compliment thrust washers like the new Ford blocks do? Tuners used to use Pinto (if I remember correctly) thrust washers in Twincams etc at one time to give the same effect. They have tabs on them to stop them spinning in the block.
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PostPost by: rgh0 » Sun May 03, 2020 4:16 am

Continued with the cleaning and dismantling and inspection of the cylinder head


Pulling the valves out. My spring remover is a large deep throat one but still needs an extension to get into the valve spring pockets on a Twincam. The extension at least give something to catch the collets as they come out.

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The valve train components are all good except some damage to No 4 inlet components where the follower was rocking in the unexpected badly worn follower sleeve bore. The rocking follower had been contacting the side of the spring and this had pushed the spring around damaging the spring seat. The rocking follower had also enabled the shim to contact the sides of the pocket it fits in in the titanium follower damaging the top of that.

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Valves all out. I use lots of these multi compartment plastic boxes for storing components in the correct order

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Removing all the studs from the head. I use a roller type stud extractor. Three rollers inside sitting on sloping ramps grip the stud when tightened to make removal easy and quick with not damage to the stud. Deep enough reach to get down over the extended studs that hold the cam cover.

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For removing the hollow cam cap dowels that have remained in the head when the cam caps are removed I have a dowel puller. The split collet fits over the dowel and is compressed by tapping a tapered sleeve over it with the slide hammer. Then an upward tap with the slide hammer and the dowel comes out. The tool then fits in a release holder and is tapped on top to release the tapered sleeve and out comes the dowel. Takes about 5 seconds and no damage to the dowel ever !

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The head casting now has all removable parts off except for the seats, guides and sleeves and ready for more thorough cleaning and measurement



to be continued......

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PostPost by: rgh0 » Sun May 03, 2020 5:08 am

Continuing with cleaning and closer inspection of the cylinder head

I use CRC gasket remover to help removed the stuck gasket material and carbon from the head. Spray it on and it softens the deposits so the gasket faces can be easily cleaned with a spatula and plastic pot scourer and the carbon on the cylinder head combustion chamber and ports wipes out with a rag.

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With the head cleaned up I can now have a close look at the worn No.4 inlet follower sleeve to try to understand whats happened there. As you may remember if you have been following this thread I pulled out the engine due to loss of power due to it partially seizing when a bearing spun in No.3 cylinder rod big end. I was lucky it did not have a catastrophic failure due to that. I now realise I was even luckier as the amount of wear on the follower sleeve could have caused all sorts of damage if the follower had jammed in the worn sleeve bore and broken

No.4 inlet follower sleeve on the left. The hour glass wear is clearly visible compared to No.3 inlet on the right. The wear is even and smooth and polished with no sign of abrasive damage or of anything jamming in there.

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No 4 measures 37.07 mm top, 35.50 mm middle and 38.10 mm bottom
No 3 measures within the standard tolerances with only a very small amount of wear, 34.94 mm top, 34.92 mm middle and 34.94 mm bottom. All the other sleeves are similar to No.3 Inlet and within new specification tolerances. Why just No.4 inlet sleeve has suffered such extreme wear of up to 3.2 mm into an hour glass shape is not clear

Close up of the No.4 inlet sleeve

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The followers show no wear or damage either in No.4 inlet or the other cylinders. All are at their original 34.91 mm diameter with no sign of wear into a barrel shape. The contact pattern from the cam is a smaller diameter on No.4 follower ( left) due to it rocking in the sleeve for an extended period but there is no damage to the surface and the follower has clearly been rotating normally like the others. The followers are long skirted lightweight steel ones ( 24.2 mm) suited to the smaller cam base circle of 1.01 inch / 25.65 mm with the 0.46 inch / 11.7 mm lift cam I am using on the inlet

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All the cam lobes are also undamaged and not worn including no 4 inlet

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The only possible explanation for the wear appears to be due to to soft sleeve material in this particular sleeve. I will get the sleeve material hardness tested in No. 4 versus the other sleeves when I take the head to the machine shop for the sleeve replacement. Hopefully the other sleeves are hard enough and its just this one that needs replacing. I would be interested if anyone has ever seen such rapid and extreme wear in a follower sleeve before ? I have never seen it before in any engines. I have seen wear in follower sleeves in high mileage twink cams but never to this extent and never in a race engine with just 3 years and around 100 hours use.

I will replace the spring, retainer, follower and valve to just be safe, I wonder if I can just buy a single one of each rather have to break up a full spare set of 8 I have?

Next week end I will have a closer look at the crank and rods to see what works is needed there . Hopefully it will be warmer in my garage then. This weekend has been the coldest start to May on record in Melbourne with half a metre of snow in the mountains to the North.

to be continued .........

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PostPost by: 2cams70 » Sun May 03, 2020 8:09 am

How is the internal oil feed in the inlet cam? Any debris in the passages particularly at the end behind the blanking plug and toward the end journals? I'd also be checking the "long sprocket bolt" modification to check that the oil flow had not been blocked or reduced by this there too. The extreme wear on the followers may have been the original source of metal wear chips leading to a cascading sequence of events that might not otherwise have occurred even with the oil filter being bypassed due to the dislodged oil pump blanking plug.
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PostPost by: rgh0 » Sun May 03, 2020 8:27 am

2cams70 wrote:How is the internal oil feed in the inlet cam? Any debris in the passages particularly at the end behind the blanking plug and toward the end journals? I'd also be checking the "long sprocket bolt" modification to check that the oil flow had not been blocked or reduced by this there too. The extreme wear on the followers may have been the original source of metal wear chips leading to a cascading sequence of events that might not otherwise have occurred even with the oil filter being bypassed due to the dislodged oil pump blanking plug.



The wear on the follower sleeve has occurred over an extended period of time I think as it is very smooth and polished and the follower itself undamaged, as it wore very fine particles would have come off . Yes metal from that sleeve wear circulating through the engine when the filter bypass plug came loose may have then resulted in the rod bearing spinning. I will try examining the wear particles in the engine to see if I can identify sleeve wear particles from bearing wear particles but the steel bearing backing shell was also worn once it spun so I probably will not be able to distinguish.

I have not pulled the cam shaft plugs yet but there will be bearing metal through them and through all the oil passages in the head, block and crank as I can see particles sitting in most of the bearing oil feed holes. Every oil passage in the engine will need cleaning.

The long bolt modification I don't believe is the source of the problem, the bolts themselves have been used in a number of engines over the years with no oil feed problems and the current cam installed 3 years ago when the engine was built was thoroughly cleaned internally with the end plug removed after it was tapped for the long bolt fitting.

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PostPost by: Donels » Sun May 03, 2020 11:40 am

Rohan,
I have seen this type of wear before on a friends Triumph Stag shortly after he had lapped the valves. It was on all tappets he had lapped. We concluded it was inadequate cleaning after lapping leaving debis in the bores.
I suspect the hourglass shape (like a cooling tower) is from debris being trapped in the middle, whereas it gets pushed out at the ends.

Hmm, looking at you picture again I see the wear is on the horizontal axis and not the vertical, so the above may be not applicable.

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