Cam Followers

[andyhodg]

Hi

Is there a way to asertain the wear between the cam follower bucket and the steel guide insert in the head? Preferably without removing the cams. I get and occasionnal "tappet" sound when the engine is idling. The valve clearances are fine. What sort of clearance should there be?

Regards

Andy

[TeeJay]

Andy.

The +2 Workshop Manual states that the Follower to Head clearance: - =0.0005/0.0014in, (0.013/0.036mm)

So if you have a narrow feeler blade = 0.0015in and you can push it down between the bucket & guide then its getting close to oversize. Use larger sizes to check how much oversize. Using round wires of the correct diameter is better still.

I had to replace one of my Buckets & Inserts as the insert was partially scored ? way down and on the odd occasion it would pick up, so giving an additional ?tappet? sound.
My concern was at some point it may stick and then damage the valve/piston etc.

Hoping that yours are OK.

[rgh0]

The buckets wear in a barrel shape and the liners wear in an hourglass shape resulting in the buckets rocking in the liner and you get the resultant tapping.

Possible to measure in situ as described but hard to get a good measurement due to the wear shape without removing the buckets and measuring wear along their length with a micrometer and similarly measuring wear along the length of the sl;eeve with a bore guage.

cheers
Rohan[quote][/quote]

[andyhodg]

Thanks for the response guys. I've just measured the buckets with a 1.5 thou feeler gauge, as TeeJay suggested and the feeler enters down the side of the exhaust followers only by about 7 mm. This is expalined by Rohan's explanation of the wear pattern but is it excessive? Does this mean I need to get the pockets re-sleeved or is there another remedy?

Regards

Andy

[rgh0]

Sounds like you have wear past the specification limits and this is producing the noise. Lots of engines run for many years with tapping buckets but if they wear bad enough they can seize in the head by cocking sideways and jamming and give problems if that happens. But if you can only just get a 1.5 thou feel 7 mm down you are a way away from them jamming I would think.

I would remove the buckets and measure it up properly and see how much wear in buckets and sleeves. If your trying to save money you may be able to get away with just a bucket replacement. Oversize buckets used to be avaialble and if you can still get them you can hone the sleeves and replace the buckets, but needs a head off to do this so not a small amount of work. The ultimate fix is new sleeves and buckets, get the tolerances right and with modern synthetic oils,regularly changed and your good for another 200k miles.

regards
Rohan

[andyhodg]

Thanks Rohan

You have confirmed what I already thought but needed some support before going down the head removal route. I will investigate the availability of oversize buckets. However to compond the problem The head was re seated about 9 years ago (approx 15,000 miles)and due to problems in achieving sufficient valve clearnace lightweight "racing spec"? buckets were fitted. I would guess that I need to go down the resleeve route.

Thanks for your help.

Andy

[TeeJay]

Andy.

As Rohan has suggested, at this stage, measure the buckets and sleeves.
This can be done without removing the head.

The amount of wear appears low, but using a feeler gauge is indicative only.
By careful measurement you will know what the situation is across all buckets and sleeves. Hopefully it will confirm your first measurement.
If the wear is much worse, then the good news is that you have prevented major engine damage.

The difficulty with any advice is understanding what your knowledge/experience is and what workshop tools you have or can borrow.
I do have all the measuring equipment, which you are welcome to make use of at my location.

With the cam cover off, engine set to T.D.C., and the Timing Marks on the sprockets correctly lined up. The Timing Chain tension adjuster completely slacked off, you can remove the sprockets and then the cams.
NOTE: - Before removal ensure that the timing chain is secured to prevent it falling into the front cover.

Everything must be spotlessly clean and each item suitably identified to ensure correct replacement.

With the cams removed you can then carefully measure all the bucket dia?s. I suggest a minimum of 6 measurements per bucket. 1 each at the top, middle and bottom then rotate the bucket 90 degrees and repeat.
The same checks need to be made on the sleeves with a bore gauge.
All the data is recorded and the evaluated.

The comments you make regarding the replaced valve seats and the subsequent difficulty with valve clearances is of concern. Were new valves & valve guides fitted?

If you intend to do any work on the engine, then I would recommend that you obtain the book ?LOTUS Twin Cam Engine? by Miles Wilkins. It can be difficult to get.

[elj221c]

The amount of wear appears low, but using a feeler gauge is indicative only.

You really need to use a wire gauge. However, if you can get down with a feeler that far (about half the depth of the bucket?) I would say the wear is excessive. There again, as Rohan says, to get a proper evaluation, each individual needs to be looked at. Buckets out! It is probably only one that is the culprit.
QED honed the sleeves in my (very old and worn) head a thou over and supplied buckets/followers of the appropriate size, so it can be done.

Roy
'65S2

[elj221c]

If you intend to do any work on the engine, then I would recommend that you obtain the book ?LOTUS Twin Cam Engine? by Miles Wilkins. It can be difficult to get.

Unless you have ?95! http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT

Roy
'65S2

[Galwaylotus]

If you intend to do any work on the engine, then I would recommend that you obtain the book ?LOTUS Twin Cam Engine? by Miles Wilkins. It can be difficult to get.

I spoke with Miles recently and he thinks a reprint will be available by the end of the year. I'm making sure it's on my family's Christmas list for me!!

[andyhodg]

Trevor

I am not concerned over the issue with the clearances. A previous owener had the head ported and tuned by Vegantune bringing it close to big valve spec but not using big valve parts but their own with reground cams to their profile.

QED carried out the re seating together with new valves and guides. The issue was getting replacement vlaves that exctly matched the ones Vegantune fitted sometime in the 70's or 80's.

I have the equipment to measure outside diameters, do you think an electronic vernier would suffice to measure the ID of the sleeves? The vernier display shows a figure down to 1/10th of a thou.

Regards

Andy

[TeeJay]

Andy.

The bores need to be measured either by an internal micrometer or a Bore Gauge, both give a small point contact.
The vernier being a "blade" contact, will not measure correctly.

If you cannot borrow these from any of your contacts, you are very welcome to borrow mine.

Great to hear you have no other head complications.

[andyhodg]

Thanks Trevor

I'm not planning to start the work until after the NEC show. However you are not that far from me and I'm often up and down the M6 for work so I will probably take you up on your offer regarding the bore gauges in December. I will be able to bring the head up and carry our a quick measure.

I'll drop you a PM nearer the time.

Thanks

Andy

[TeeJay]

Andy.

I would suggest you first measure the cam follower sleeves with the head still assembled, that is unless you intend to carry out other work?
Also no problem if you do what to bring the head to my home for measurement.

I note that your car may be on the LDC at the NEC, so I assume that?s why the December start date.

There is a small possibility that I may go to the NEC, depends on the outcome of my visit to the Malvern Club Lotus Show this Saturday.
So if I do go to the NEC I could bring the Bore Gauges with me and we could meet up.

Or as above, I will await your PM

Regards.

[andyhodg]

Trevor

I thought that to use the bore guages I would need to remove the valves? I realise I could measure the topmost part of the bore but to do the job properly I imagine I would need to measure top, middle and bottom.

If you do go to the NEC then it would be good to meet. I will be there o the Friday and Sunday.

Regards

Andy