Lotus Elan

Lotus Twin Cam - Cam Bearing Inspection

PostPost by: dlb123 » Thu Jan 19, 2017 5:10 pm

Hi there. New and the forum and new to lotus. Inhereted my Dad's +2 and since Im a glutton for punishment, Ive decided to restore it to its former glory.

Currently dismantling the engine, and have got as far as disassembling the head. The engine was completely rebuilt by Mick Miller around 15 years ago, and has only done 11000 miles since that time. To my knowledge, has not been run without oil, or overheated (according to my rather mechanically unsympathetic father).

I am taking it apart because it leaked oil like a sieve, and I also want a good look at it before it goes back in the car.

I am relatively inexperienced when it comes do engine diagnosis. I have included two photos of the cam bearings. From what I can see, the majority of the wear is on the upper halves of the bearings (the ones that sit in the cam caps/retainers). Is this wear typical of such a young engine? Theres some deeper scoring as well if you look closely. Any input would be much apprecated. Could this be from overtightening, oil pressure loss, warped camshafts? I am lost .

Thanks a lot, Dave
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PostPost by: Davidb » Fri Jan 20, 2017 4:54 am

Dave, since no one else has offered an opinion I will. The scoring may have been caused by somebody, possibly the original builder, possibly not, over torquing the cam bearing bolts-I forget what the torque rating is but the caps are just aluminium and crush easily. I managed to do this on an Aston Martin engine some time ago...
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PostPost by: StressCraxx » Fri Jan 20, 2017 6:20 am

Hello Dave,

I think what you observe is not uncommon for a twincam. Most twincams sit for periods of time and the oil drains from the bearings. It takes multiple turns of the engine to build oil pressure after sitting a while and what you see is the result. The valve springs push the cams up into the caps and that is where you see the wear.

After re shimming my valves, I have reassembled bearings that looked like them and run the car for another 10,000 miles without worry. Then I checked clearance, reshimmed and ran for another 10,000 miles before I pulled the head to freshen all of it.

Oil leaks have several sources - The timing cover to block and head, the cam bore plugs at the back of the head, the oil breather tube between the block and the head, on the right side above the starter, and of course the valve cover gasket. Most of the gasket fits after 40+ years are in poor condition. Scrupulously clean and then check for flatness on a surface plate. Resurface the warped faces and reassemble with the specified torque in the manual.

Reassemble with a professional anaerobic sealant or Permatex "Right Stuff".

Since you have the cams out, remove the follower buckets and carefully inspect all of the valve springs, looking for any indications of broken springs, both inner and outer springs. Expect to rebuild the water pump since the car has sat so long. The coolant weeps from the mechanical seal face and causes the needle bearing to rust away.

With members' help such as Davidb and others, like Rohan I think you will do well.

Best regards,
Dan Wise
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PostPost by: RichC » Fri Jan 20, 2017 8:50 am

it is not uncommon for cam bearings to be left rather than be changed during rebuilds (!). Might these be the originals?
My engine was completely professionally rebuilt by PO in mid nineties and on inspecting all the receipts there was no mention of new cam bearings; virtually everything else was replaced but not these . I remember inspecting them on purchase back in '09 and they had similar marks to yours-which i put down to crap in the oil and long time being stood idle before engine was cranked over by me 13 years later.
I replaced the original cam bearings only this winter . I must say the oil pressure is much improved :D
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PostPost by: dlb123 » Fri Jan 20, 2017 9:02 am

Thanks to both of you for your responses. Stresscraxx, what you described certainly makes sense, given that the car was stored in a barn for 6 years and started once or twice a year by my father, albeit with much swearing and cranking of the engine.

Given that the engine is already apart, would it not be prudent to renew the cam bearing shells? Further to that, there is some very light scoring on the cam journals. I imagine some polishing and a check of trueness would be sensible at a local machinist, to ensure the camshafts are in good health? Forgive my ignorance. I spent some years rebuilding motorbike engines, but my remit was replacing knackered bottom ends that were obvious to a novice like myself.

Interestingly, re the flatness of the sealing surfaces, I have found the back plate of the timing cover to be a little warped. Is that something that could be faced? Or perhaps pressed flat again?

I have since pulled the bottom end and all seems remarkably healthy. The crank was reground, as per the receipt from mick (God rest him), and the bearings are all evenly worn. I still think I'll replace the shells. It's difficult to know what to do, in terms of crack testing, block pressure test etc, since I'm hoping this was all done when it was rebuilt some years ago. I have no reason to suspect anything untoward from the engine, other than a rather tappety sound from the top end.

I digress. This internal monologue is becoming tedious!

Any input appreciated greatly.

Dave
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PostPost by: nigelrbfurness » Fri Jan 20, 2017 9:28 am

I agree with Dan. I have stripped many TCs over the years and the appearance of the cam bearings is typical of a fairly reasonable, even low, mileage. Oversize cam bearings have never been available to my knowledge and most people simple replace them at a rebuild and use the camshafts again unless significant wear of the bearing journals or other wear is present. It is not one of the TC's weak areas, IMHO. Although the journals have a small diameter, they do not get the same punishment as mains and big ends and the shafts themselves are very stiff.

Regarding your warped backplate - again, this is quite common. Press it flat and have it checked on a surface plate, you can skim them but replacements are usually obtainable and a better option. I would not skim more than a couple of thou of one though.

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PostPost by: rgh0 » Fri Jan 20, 2017 11:45 am

Your cam bearings are excessively worn. They need to be replaced. Many twin cam engines suffer from rebuilds where the cam bearings were not replaced and are excessively worn, they are expensive so many people skip replacing them. As a result the oil floods the head and the level in the sump drops excessively leading to loss of oil pressure especially on right hand corners. The oil flooding in the head also leads to a smoky exhaust as the excess oil is sucked down the inlet guides

People then put restrictions in the oil passage to the head and starve the cam bearings and wear them even more :twisted:

cheers
Rohan
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PostPost by: Elan45 » Fri Jan 20, 2017 3:17 pm

You were mentioning scoring in the bearing shells. I cannot see it, but I have not tried to enlarge your photos.

But, I should caution you to not allow anyone to glass bead blast of other blast medium as there are places in the TC head where the beads can get lost, but they will come out under running conditions and do nasty things to an engine. Clean only with liquid solvents.

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PostPost by: StressCraxx » Sat Jan 21, 2017 3:11 am

rgh0 wrote:Your cam bearings are excessively worn. They need to be replaced. Many twin cam engines suffer from rebuilds where the cam bearings were not replaced and are excessively worn, they are expensive so many people skip replacing them. As a result the oil floods the head and the level in the sump drops excessively leading to loss of oil pressure especially on right hand corners. The oil flooding in the head also leads to a smoky exhaust as the excess oil is sucked down the inlet guides

People then put restrictions in the oil passage to the head and starve the cam bearings and wear them even more :twisted:

cheers
Rohan


Rohan,
I will defer to your experience. I did not see evidence of any babbitt wipe, just a polishing of the shells in the caps. I guess didn't have a close enough look at Dave's shells with my monitor last night. I miked my bearings the last time I checked and shimmed my valves. They were on spec or less than 0.001" for each (not a race motor, a stock street motor). I don't find the cam bearing shells that expensive. I think he paid $80 for the set when I helped my friend freshen his Twink head last year.
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PostPost by: rgh0 » Sun Jan 22, 2017 11:11 am

StressCraxx wrote:
rgh0 wrote:Your cam bearings are excessively worn. They need to be replaced. Many twin cam engines suffer from rebuilds where the cam bearings were not replaced and are excessively worn, they are expensive so many people skip replacing them. As a result the oil floods the head and the level in the sump drops excessively leading to loss of oil pressure especially on right hand corners. The oil flooding in the head also leads to a smoky exhaust as the excess oil is sucked down the inlet guides

People then put restrictions in the oil passage to the head and starve the cam bearings and wear them even more :twisted:

cheers
Rohan


Rohan,
I will defer to your experience. I did not see evidence of any babbitt wipe, just a polishing of the shells in the caps. I guess didn't have a close enough look at Dave's shells with my monitor last night. I miked my bearings the last time I checked and shimmed my valves. They were on spec or less than 0.001" for each (not a race motor, a stock street motor). I don't find the cam bearing shells that expensive. I think he paid $80 for the set when I helped my friend freshen his Twink head last year.


From the photos it looked like the top layer of the bearing shell had worn off. If it is just polishing not signficant wear then check the bearing clearances with plastigage and if within specification you don't need to change them.

cheers
Rohan
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PostPost by: Quart Meg Miles » Sun Jan 22, 2017 11:00 pm

Welcome Dave! What variant and/or year is your car?

I had a S130 which insisted in wearing out its front exhaust cam shells despite everything being in line. The engine ran fine and eventually I just ignored it; I notice one of your shells seems worn more than the others.
Meg

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PostPost by: wobblyweb » Sat Feb 11, 2017 6:34 pm

Your cam bearings are excessively worn. They need to be replaced. Many twin cam engines suffer from rebuilds where the cam bearings were not replaced and are excessively worn, they are expensive so many people skip replacing them. As a result the oil floods the head and the level in the sump drops excessively leading to loss of oil pressure especially on right hand corners. The oil flooding in the head also leads to a smoky exhaust as the excess oil is sucked down the inlet guides


Rohan, why would worn cam bearings cause excess oil in the head?
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PostPost by: rgh0 » Sat Feb 11, 2017 9:57 pm

Worn cam bearings lead to a much increased oil flow into the head through the bearings. This floods all the drain passages and a higher level of oil builds up in the head.

There are two impacts of this.

1. More oil gets sucked down the valve guides becasue the level can build up above them and you can have a smokey engine
2. The oil level drops in the sump because so much oil is in the head and you have greater loss of oil pressure problems in right hand corners

people often put restrictors in the oil passage to the head to prevent this especially on competition engines fitted with HP/ HV pumps when really they should be replacing the cam bearings

cheers
Rohan
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PostPost by: wobblyweb » Sun Feb 12, 2017 9:36 am

Thank you Rohan, as far as I know my cam bearings are the original ones. At least in the 37 years I've owned the car they have never been replaced.
I do get blue smoke on the over run but put that down the valve guides. I will replace the bearings now, will the tappets need re shimming? I guess at least checking would be wise.

Thank you
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PostPost by: RichC » Sun Feb 12, 2017 10:21 am

tappets shouldn't need reshimming ...
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