Lotus Elan

Removal and rebuilding of a Twincam

PostPost by: elanner » Tue Apr 14, 2020 11:12 am

rgh0 wrote: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.


Rohan,

The answer to this is the wonderful Snap-On S9465A. 17" long, makes getting the the front pulley easy.

Made between 1953 & 1967, I believe for an automatic transmission of some type. Surprisingly, they come up on eBay quite regularly - there are two available right now, although both of them are asking twice what I paid for mine, so perhaps it's worth waiting for a better deal to come up.

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PostPost by: benymazz » Wed Apr 15, 2020 12:27 am

Good catch Rohan... I love seeing engine autopsies. Obviously no failure is ideal but once that ships sails all that's left is to find out why it failed and see what you can learn and improve for the next time around. That and some swearing about how much money it's going to cost you...

I have a recent story that roughly parallels yours with a different ending though. My neighbor has a 2004 Subaru WRX that had about 185k miles (300k km) on the original engine. He bought it in fall of 2019, cranked up the boost on it and tuned it to give about 305 hp at the wheel... knew he was pushing it; the rings were starting to go, but I digress. A couple of months ago he was driving some backroads in a spirited manner (as 18 year old boys are wont to do) when he noticed that he seemed a little bit down on power. He was about 15 minutes away from his house so he turned for home and started limping it back. A couple of minutes later, the engine started knocking. It broke the no. 2 connecting rod about 6 minutes away from his house and the engine seized in his driveway.

No surprises, what was left of the #2 bearing was almost welded to the journal. That was clearly the first thing that had gone wrong and triggered everything else. Once the teardown was complete we cited the cause of death as "complications due to a spun bearing" :lol: . The engine was a writeoff obviously - hole in the block, crashed the piston into the head, bent the valves... but a week later he bought a JDM engine off eBay and now it's back on the road... living to die another day, possibly when the transmission grenades itself.

Not sure how rapidly a spun bearing on a race TwinCam goes from "bad" to "disastrous" but it can't be very long. Paraphrasing what you or someone else said above, if you kept driving it that could've been a very expensive several minutes :|
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PostPost by: Matt Elan » Thu Apr 16, 2020 8:14 pm

Thanks Rohan for taking the time to post this - it’s fascinating. Hope there isn’t any other damage and you get away with just new shells and a quick polish of journals
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PostPost by: rgh0 » Sun Apr 19, 2020 12:36 pm

Time now to fully dismantle the engine for closer examination of what other damage may have been caused by the bearing failure and metal circulating through the engine due to the filter bypass pluh having come loose.

IMG_8326 (1).jpg and


First I lock the flywheel in place. This is an old sample piece I made about 50 years ago when in University. We did an 8 week full time workshop, machining and welding course at the end of 2nd year which was great training for young mechanical engineers, sadly they don't do this now

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Having locked the flywheel remove the front pulley bolt and pulley and while your there remove the water pump pulley also. I use a smaller 3 inch diameter steel crank pulley to keep the water pump and alternator revs down when the engines at 8000+ rpm. Note also the 2 jacking screw holes in the pulley to make it easy to remove if stuck

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Now remove the clutch pressure plate , note the balance markings on the pressure plate and flywheel.
With the pressure plate off, the flywheel face is in good condition and you can still see the machining marks despite 3 years of drop the clutch at 4500 rpm race starts.

5 bolts for the modified Datsun L16 forged steel crankshaft and a lightweight steel flywheel

more to come
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PostPost by: rgh0 » Sun Apr 19, 2020 1:09 pm

Continuation of engine dismantling for clean and inspection

IMG_8325 (1).jpg and


Flywheel still locked and a long breaker bar to remove the flywheel bolts without straining myself :lol:

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Flywheel off and back of the lightweight steel flywheel. Ring gear unmarked thanks to use of pre-engage starter

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Now to start work on the head. Head number GR 20 and McCoy conversion 51

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Cam cover off. Gasket is stuck to the head with Loctite Aviation gasket cement. A sharp spatula enables the gasket to be cleanly removed. Note the degree of compression on the cork gasket. You need to compress it by around 30% to 40% of its original thickness. I measure this gasket compression to ensure its even over the whole cover rather than rely on torque of the cam cover nuts. Head is actually from a Europa originally you can see the location at the inlet cam rear for the seal on the extended camshaft that drove the alternator

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All looks OK with cam lobes and followers with no damage evident from the metal in the engine. I used adjustable sprockets on this engine. Easier to set up than the offset dowels I have used previously.

to be continued
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PostPost by: 1owner69Elan » Sun Apr 19, 2020 5:34 pm

What pressure plate are you using? Brand ? Rating? Vs your engine output?

I see either a white or gray paint dot.

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PostPost by: 2cams70 » Sun Apr 19, 2020 11:37 pm

I'd be interested to know what kind of starter ring gear you are using with the pre-engage. Is it one with a lead in on both sides or did you just reverse the standard gear? From the photo yours looks a little unusual with teeth longer than normal and on a slight angle - could just be an optical illusion from the photo though.
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PostPost by: rgh0 » Mon Apr 20, 2020 12:34 am

1owner69Elan wrote:What pressure plate are you using? Brand ? Rating? Vs your engine output?

I see either a white or gray paint dot.

Thanks


I use the AP racing pressure plate from Burtons SKU CP2246-71 with a locally supplied Exedy clutch plate. Works perfectly with my 180+ HP 1600 cc engine

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PostPost by: rgh0 » Mon Apr 20, 2020 10:15 am

2cams70 wrote:I'd be interested to know what kind of starter ring gear you are using with the pre-engage. Is it one with a lead in on both sides or did you just reverse the standard gear? From the photo yours looks a little unusual with teeth longer than normal and on a slight angle - could just be an optical illusion from the photo though.


Standard starter ring gear with lead in bevel both front and rear. The angle of the photo creates the impression of longer and angled teeth. I think. i have run the same Bosch prengage starter from 70's Fords on flywheels with no lead in on the engine side where the pinion comes in from without problems

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Last edited by rgh0 on Sun Apr 26, 2020 4:19 am, edited 1 time in total.
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PostPost by: Davidb » Mon Apr 20, 2020 5:45 pm

I just checked the Burton site-it says clutch pressure plate is NLA...
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PostPost by: 1owner69Elan » Mon Apr 20, 2020 9:22 pm

As noted, the AP CP2246-71 is NLA. Discontinued

However, when I get the engine pulled, I’m anticipating that I have the same, as supplied earlier by Dave Bean (2015). Ken Gray at Bean indicated it was the "highest rated Elan AP clutch". TBD

Seems that the recommended replacement for this discontinued AP clutch cover is the Helix 60-3331 (TTR supplies). Rated at 160 lbft torque. The AP seems to be rated at 165. Bean's old catalog says 170. In any case all within range for my 143 lbft.
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PostPost by: Davidb » Mon Apr 20, 2020 10:10 pm

Rohan: I googled that helix number and Demon Tweeks have it:
demon-tweeks.com/helix-standard-cover-assembly-hlx60-3331/
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PostPost by: 1owner69Elan » Mon Apr 20, 2020 10:34 pm

Also, the associated friction plate for the T9.

https://www.demon-tweeks.com/us/helix-7 ... lx70-2619/

Listed in the Helix Catalogue as for the MGB:
Helix.jpg and



Now, let's get off the sidetrack and let Rohan get back to his Twincam.
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PostPost by: rgh0 » Sat Apr 25, 2020 6:07 am

Continuing with the engine dismantling


Removing the cam chain adjuster bolt
IMG_8342 (1).jpg and


Removing the camshaft sprockets - note the long cam bolt to prevent cam breakages buy putting the front section of the cam from the sprocket to the first bearing under compression from the bolt.

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Thermostat housing off - note air bleed hole in thermostat

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Removing the cams. Take care to release the bearings evenly a little at a time to allow the cam to be pushed up by the valves that are still open without getting excessive bending stress in the cam by having one end clamped down with the other released and the valve springs pushing up on the free end. I use a tube spanner for quick removal and to reach over the long cam cover retaining studs.

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Some cam bearing damage from the metal through the engine but not catastrophic and no damage to cams or cam shaft journals

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I use a lot of these multi compartment plastic storage boxes. Easy to see whats in them to find parts and easy to keep parts in order so they go back in the same place.

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Using a valve grinding sucker stick to remove the cam followers. The shim generally comes out with the follower stuck to the follower shim pad with a film of oil.

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When I got to No4 inlet follower it was rocking in the sleeve bore. You can clearly see the wear in the sleeve at the top as the sleeve wall remaining gets thinner towards the cam sides where it carries sideways load from the cam turning. The wear appears limited to just the top section of the sleeve and the followers are undamaged . High lift cams ( I am using 0.46 inlet) with a small 1.010 base circle can give this problem as the longer follower comes out of the sleeve further than normal putting more load on the sleeve. It appears only one sleeve has suffered this failure but I will need to measure them all carefully once the valves are removed. I will need to think about ways to reduce the risk of this in the future. Another item of machine shop work to be done replacing the sleeves where needed

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to be continued .......

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PostPost by: rgh0 » Sat Apr 25, 2020 6:34 am

Continuing now with the head removal

First take of the front 3 bolts to the front timing chain cover

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Remove the nuts from the ARP head studs

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Remove head studs using the hex socket in their ends. With the studs in place it is extremely hard to remove or replace the head due to the tight hole fit and not perfect location and alignment.

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Head of the block and front cover cork gasket was sealing OK and not over compressed

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Bores and pistons all look Ok

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Head looks OK

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remove the chain adjusting sprocket and swing arm bolt

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Composite head gasket 85 mm fire ring bore for the 83.5 mm engine bore all looks like it was sealing well with no sign of damage apart from what the removal has caused.

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The head with the valves in it will be put aside for later dismantling and more careful inspection and measuring but apart from the damaged No4 inlet follower sleeve all the rest looks good so far.

The dismantling of the block follows in the next episode

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