Hepolite Pistons drain holes

[ivan.wood]

I have been watching the site for some time as I am rebuilding a 1965 Elan S2. History of the car is in short supply but was bought by a doctor in NJ I believe. It was bought by a friend of mine but due to medical problems was unable to restore it. I bought it from him but as I began to work on the car I found it had been in at least one major crash and although the body had been poorly repaired but not the frame which probably meant it never drove straight or cornered properly.

I am into year 3 of the restoration and am working on the engine which appeared to only have 46,000 miles according to the speedo so not a lot of wear. I managed to get a set of NOS original Hepolite pistons but I notice my old ones have 8 holes (4 either side) in the scrapper grove and the new ones only have 4 total. Does anyone know why this is, were the ones with 8 holes an later development to improve either oil clearance or better bore lubrication or may be to improve lubrication of the small end bearing? I can drill extra holes but would like to be sure it is the correct option?

Any thoughts on the reason.

[Craven]

As there are no other offerings.
Twin cam does suffer from bore oil clearance, some engine builder drill extra drain holes in the angled land below the oil control ring.
FWIW

[ivan.wood]

Thanks I was wondering if they were of a Series1 engine as I do not know how old they are. The other thing I noticed were all the old pistons are the some weight (511gms) but the new ones vary by up to 5 gms (525 to 530 gms) which does not appear to be very good quality control by Hepolite?

[Craven]

I think original pistons supplied to Lotus were Tin Plated, this give a greyish tint on the outside.
PowerMax was the preferred Hepolite piston for rebuild.

[types26/36]

I have a set of new standard lotus pistons which I have had for many years......they were dead stock from a lotus dealer.
They have 8 drain holes, the only markings on the inside are cast in AM 413.

[ivan.wood]

Thanks for the photos at least I know there should be 4 holes per side. I am still worried about the weight difference although the Lotus manual states 4 gms between piston and 6 gms for conrod and piston so I am within there 6 gms.

Has anyone more recent information on unbalanced weight of pistons etc on engine vibration?

Thanks

[denicholls2]

Thanks for the photos at least I know there should be 4 holes per side. I am still worried about the weight difference although the Lotus manual states 4 gms between piston and 6 gms for conrod and piston so I am within there 6 gms.

Has anyone more recent information on unbalanced weight of pistons etc on engine vibration?

Thanks

I can't speak to the variability expected in as-received machined pistons or whether you have sloppy ones, but tight tolerance from the factory is something the Japanese taught the automobile world (or the non-racing part of it at least) after the 1960's.

Standard practice of a performance engine builder/rebuilder would be to match all components for weight to a tight tolerance by filing a non-contact area of the heaviest parts down to the weight of the lightest one (pistons, connecting rods). Absent better information, I would assume this was done with your originals but not yet with your new ones. There is generally a recommended spot to do the matching that has a minimal effect on balance, etc. Careful examination of your originals may reveal where this was done.

[knockoffnut]

All of the twincam pistons I have seen have had the eight holes. I have seen other engines with oil holes only on one side of the piston, maybe crossflow pistons only had four?? Or maybe it was a running change early in twncam production. I would add the holes so that you have eight holes, four through each side as shown in the pictures. I always try to balance pistons within 1 gram of each other, and also balance each end of the rods to within 1 gm of each other. It makes a smoother running, sweeter engine.

[knockoffnut]

Being more out of balance will add extra vibrations that you may or may not notice, and vibrations do accelerate the wear of the moving parts, as well as creating small power losses (which may not be measurable). The beauty of being fussy about these kinds of things when you build your own engine, is that it doesn't cost any extra, the engine runs sweeter, and it may allow some extra revs at the top end, ie. it may stop your engine from granading on over-revving. While you are at it, it pays to soften the sharp edges on the piston top, and in the combustion chamber to delay the onset of pinging (pinking) and knock with currently available fuels.

[types26/36]

As I recall Ford XFlow pistons did not have oil drain holes, they had a long slot in the oil grove making them weak compared with TC pistons.
The OP has a set of Heplolite pistons and I dont think Lotus ever fitted Heplolite as standard, the Hepolites were non OE after market supplied, also Lotus only ever supplied +15 thou oversize TC pistons and as far as I know Hepolites came in standard and increments of +10 thou (I might be wrong there though so happy to be corrected)
Edit: XFlow piston picture added

[ivan.wood]

I am now thinking the new pistons may not be Lotus and possibly for the standard Ford 1600 engine, that used the same block, as the rings are FOMOCO which I believe is Ford Motor Company?

I will get my original pistons measured as they only have light scuffing on the skirt and seem to have about the same amount of play in the bore as the new ones. Unfortuately my micrometers only go to 3" so will have to find a machine shop to check them.

Thanks for the help everyone.

[types26/36]

I am now thinking the new pistons may not be Lotus and possibly for the standard Ford 1600 engine, that used the same block, as the rings are FOMOCO which I believe is Ford Motor Company?

You will immediately notice the difference between XF and TC, the XF has a "bowl in piston" combustion chamber while a TC has a slight dome and two cut outs for the valve clearance. Not only that the compression height (crown to gudgeon pin) is different.
Pic of XF piston added.
There is also the Pre-XF piston that has a flat top with no cut outs, I have seen them used in a TC with mods (valve cut-outs) as these pistons were used in the 1500 pre XF block the deck height is is almost identical to the TC.
Post a picture of your piston crowns.

[Craven]

If the oil drain behind the control ring is a SLOT then you have an early design that is known to fail,
Often people think new old stock is a good thing but not in the case of these pistons, it was a bum design and they changed to drilled holes behind the ring. Many a piston top has parted company with the skirt at this point.
FWIW.

[ivan.wood]

Mine must be Lotus pistons then because they have the valve cut outs so I am not sure where they are from, unless they came from China!!!!

I was going to upload a couple of photos but every time I try my Iphone says there is a problem and reloads the page.

[types26/36]

I was going to upload a couple of photos but every time I try my Iphone says there is a problem and reloads the page.

I think there is a restriction on the size of attachments, try resizing and have another go.