I took of the two bolts in the engine bay fixing the bodyshell to the turret of the chassie, included the two brackets for radiator and bonnet setting (how do you call this area?).

I found a surprise: the two bolts are different as shown in the pictures. On the left side there is a UNC and on the right side a UNF, both head are 9/16 in. but different lenght and bobbin clearance.

Thank you for any comments.

Umberto
Elan Sprint 7108000193K

Umberto

Who can say why there should be a difference?

I'm pretty sure my car had not been touched between manufacture and my present restoration and I have found a strange mix of fittings so guess the factory made do with what was to hand.

Maybe your car was repaired at the time (or since) by someone who had to complete the job without the correct fixings and made do!

The Lotus part number for the bolt is XUFB0620, meaning a 3/8"-24 bolt (fine thread), 1.25" long under the head, the same part for both sides. I suspect a DPO replaced one of the fine thread bolts with a coarse thread without paying attention to what was going on. The tapped hole in the frame where the coarse threaded bolt went in is now likely damaged pretty badly. You can restore the thread with a Helicoil insert or just drill a clearance hole all the way through and use a longer bolt and nut.

Hi Umberto,
Both course and fine thread bolts are used to secure body to chassis. UNF is used in the 6 locations where the bolts screw into the chassis - engine bay to front suspension towers, bottom of dashboard to top of chassis and rear cockpit to rear suspension towers. In all other locations where the bolts screw into bobbins in the body UNC is used.

The 3/8" x 1" UNC bolt which you have is normally used for the 6 fixings which go through the bottom flange of the chassis into the body floor so has been used in the wrong location. At 1" long it is only just long enough to pass through the bobbin and is probably therefore only just engaging in the thread in the chassis.

It could be that your chassis has been incorrectly tapped with a UNC thread. Try a longer UNC bolt - if it won't screw easily all the way through the chassis then the thread is either UNF or damaged (or both). If it does screw easily all the way in and you can torque it up it will probably be OK to leave it as it is but do use a bolt which is at least 1 1/4" long. If you aren't happy about it then use a helicoil or drill through and use a nut and bolt as already suggested.

Best regards,

First check if the threaded section in the chassis was cut UNC or if it is a maltreated UNF. In this case, you can try a thread restorer first - a non cutting, cold reshaping tool that looks like a mixture of bolt and cutter. I use these very often, for cleaning and reshaping tortured threads. (rescued 6 of my door window channel bobbins which were force fed with UNF bolts and are now back to UNC an don' let go!)

Anna

Russ, can you give us the info on how to decode the Lotus part # that tells what thread & length the bolt is?

The cross reference between fastener specification and part number is found in the Service Parts List, typically at page 9 or 10 depending on whether you are looking at the Elan or +2 list and which edition. I had intended to post the appropriate page here but, oddly, the PDF of the +2 Service Parts List on my laptop is missing this page. The topic has been discussed on this site as well and there has been reluctance to put Service Parts Lists and Workshop Manuals up here due to copyright concerns. The majority of standard bolts and screws used on the Elan and +2 can be deciphered as follows:

Example from my earlier post: "XUFB0620"
"X", the first character denotes the bolt or screw head configuration, "X" denotes a hex head, "R" denotes a round head, etc.
"UF" the second and third characters denote the thread type, "UF" denotes UNF (fine), "UC" denotes UNC (coarse) and MM denotes metric
"B", the fourth character denotes the fastener type, "B" denotes bolt, "S" denotes screw, "N" denotes nut, etc.
"06", the fifth and sixth characters denote fastener nominal diameter in sixteenths of an inch, "06" denotes 06/16", or 3/8" diameter
"20", the seventh and eighth characters denote fastener length in sixteenths of an inch, "20" denotes 20/16", or 1 1/4" long.

So the part number for coarse threaded both in Umberto's first post would be "XUCB0616" according to his measurements. Actually this second one is a confusing example as Lotus classified the coarse thread bolts going through the chassis into bobbins in the body shell as "screws" and they appear in the Service Parts List as "XUCS0616" although dimensionally exactly the same as a "XUCB0616" I don't know, perhaps there is a difference in the unthreaded shank length that distinguishes a bolt from a screw. I guess I made that example clear as mud. Any insight here Pelly, Esq?

This numbering system applies only to standard fasteners used in the body and chassis. Generally speaking the engine, gearbox and final drive fasteners do not follow this algorithm and Lotus used the ENFO part numbers carried over from the source. Keep in mind that many engine, gearbox and final drive fasteners are not standard hardware items. Other non-standard fasteners, such as the reduced-head-depth outboard bolts attaching the rear wishbone to the hub carrier, will have a conventional Lotus part number such as A036 D 0191.

Threads into bobbins are all coarse, threads into steel chassis fixings are fine. Coarse threads into the chassis are a mistake!

Mike

Russ:

I was curious about the bolt vs. screw thing as well. This link attempts to explain, but it is pretty confusing and standards apparently vary.

http://en.wikipedia.org/wiki/Screw#Diff ... _and_screw

The thing can apparently be considered a screw for any of the following:
1 - It is smaller than a bolt (common usage)
2 - Historically it had threads right up to the head, but article says this distinction is now obsolete
3 - It is inserted & tightened into a threaded hole (like a bobbin I guess)
4 - It is conical, like a wood screw or lag "bolt"

It appears Lotus is using number three. If the hex headed fastener is tightened with a free nut it is a bolt. If it is screwed into a captive nut, threaded hole, bobbin, etc. it is a screw? Seems inconsistent in my Plus 2 book though, as the fasteners that go through the frame to a nyloc nut front (by the steering rack) and back (by the boot floor) are called screws, and it looks like the fasteners going into tapped holes in the frame on the towers are called bolts?

Perhaps the colour blind guys from the wiring department were moved to drafting and parts identification for the summer.

Cheers!

[quote="stugilmour"
3 - It is inserted & tightened into a threaded hole (like a bobbin I guess)
It appears Lotus is using number three.[/quote]

Stu,
And of course the connecting rod, flywheel and crank pulley fasteners are listed as bolts. This is not a problem unique to Lotus, just one of those cases where engineers have agreed to be imprecise. I am waiting for Bill Gavin to set me straight on this one.