Lotus Elan

Faulty Con-rod bolts

PostPost by: Donels » Thu Jul 04, 2019 3:21 pm

I recently purchased 8 new con-rod bolts from Burton for my rebuild. Two of the bolts worried me as they seemed to stretch far more than the others before reaching the torque. I left them for a couple of weeks while sorting a water pump problem, but I was not happy with the issue.

I broke and re-toqued all 8 bolts today and these two stretched far more again. Check torqued and they stretched again. Removed and examined for necking and found both bolts had grooves in the shank which look to be over run from the thread rolling process. Removed all 8 and 4 had the grooves, see pics.

There are two issues here. The 4 bolts have stress raisers in the high stress area, which can lead to cracking and failure and 2 bolts appear to be heat treated incorrectly and do not have the required strength.

I have contacted Burton and they are clearly concerned and investigating. So if you have purchased any con-rod bolts recently be warned and check.

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PostPost by: rgh0 » Thu Jul 04, 2019 9:16 pm

What markings are on the heads of the bolts. The steel and / or heat treatment is clearly faulty as you have told Burtons to get the elongation shown. I am surprised the bolt on the right did not fail completely with that much plastic deformation it must be a very soft bolt.

A good pickup thats prevented a very expensive failure

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PostPost by: promotor » Thu Jul 04, 2019 9:51 pm

That is absolutely frightening, and is the reason to stay with original equipment or big brand names.

Have you tried a standard original bolt back in the con rod threads to see what condition they are in?
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PostPost by: 2cams70 » Fri Jul 05, 2019 12:42 am

What lubricant did you use on the threads to assemble them with? What torque specs. did you use?
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PostPost by: Lyn7 » Fri Jul 05, 2019 6:56 am

Thanks for posting this. It is of great concern when such a critical part cannot be trusted. I look forward to hearing how Burton deal with this.!
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PostPost by: Donels » Fri Jul 05, 2019 10:50 am

Markings on the bolt head are FFM 12.9, see pic.

Thread were lubricated with engine oil hence no torque reduction required. Torque figure is interesting. All Lotus manuals and references I can find quote 45 ft lbs however the Burton web site quotes 35 ft lbs for their 'heavy duty' bolts and 45 ft lbs for their ARP bolts for competition bolts. But they say the heavy duty bolts are for twin cams. A Ford Escort manual I checked also quotes 35 ft lbs. Confusion!

I used 45 ft lbs and six of eight bolts were fine but two stretched. I currently have used 4 of the old bolts (not ARP) and they are fine at 45 ft lbs.

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PostPost by: rgh0 » Fri Jul 05, 2019 10:53 am

There is no way a real 12.9 bolt will stretch that much without failure. Burtons are buying cheap counterfeit bolts which unfortunately are common.

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PostPost by: rgh0 » Fri Jul 05, 2019 11:01 am

I cant find any recognised ffm bolt maker. It is also unusual to use a metric bolt rating code like 12.9 on an imperial UNF threaded bolt. Definitely very dodgy.

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PostPost by: Donels » Fri Jul 05, 2019 11:15 am

To be fair to Burton's my guess is they purchase them from a bolt and fastener supplier who gets them from the cheapest supplier, probably China. But I agree with you somethings not right. I think the answer is to buy a known quality like ARP.
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PostPost by: rgh0 » Fri Jul 05, 2019 11:25 am

You just need be careful the ARP bolts you get are real. You can get cheap con rods completed with rod bolts claimed to be supplied with ARP bolts ( and the bolts have all the right markings) for a total cost that is not that much more than the cost of real set of ARP bolts themselves. !!! if it looks to good to be true it probably is.

Burtons may have been scammed but the same applies to them. Their buyers should know enough to know when the price is to good to be true

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PostPost by: 2cams70 » Fri Jul 05, 2019 2:06 pm

Donels wrote:Markings on the bolt head are FFM 12.9, see pic.

Thread were lubricated with engine oil hence no torque reduction required. Torque figure is interesting. All Lotus manuals and references I can find quote 45 ft lbs however the Burton web site quotes 35 ft lbs for their 'heavy duty' bolts and 45 ft lbs for their ARP bolts for competition bolts. But they say the heavy duty bolts are for twin cams. A Ford Escort manual I checked also quotes 35 ft lbs. Confusion!

I used 45 ft lbs and six of eight bolts were fine but two stretched. I currently have used 4 of the old bolts (not ARP) and they are fine at 45 ft lbs.

The attachment 06C45C2C-F46D-4824-A4FE-6E663C88E09A.jpeg is no longer available


All very interesting. The Escort manual quotes 35 ft/lb for the regular crossflow engine and 45 ft/lb for the Escort Twin Cam.

Below I have taken pictures of OEM crossflow and Twin Cam bolts side by side. On the left is the crossflow bolt and on the right is the Twin Cam. Both bolts are interchangeable physically but the metallurgical properties are quite different.
Cross flow bolt is GKN brand (UK manufacture) and grade V. Twin Cam bolt is Kamax brand (German manufacture) and grade 12.9.
Tensile strength = 65-75 ton/in2 (grade V) and 77-88 ton/in2 for grade 12.9. The difference in tensile strength explains the difference in torque specs. Kamax is a German manufacturer which probably explains the metric 12.9 grading system in combination with imperial threads.

Interesting to note too that the Kamax bolt has a dimple at the end for accommodating a stretch gauge. This means the Twin Cam bolts were probably originally torqued using a stretch gauge in production rather than a torque wrench (unless my engine has some previous history I don't know about).

Burtons or whoever sourced the bolts directly from the manufacturer obviously gave an original bolt as a sample to the manufacturer and said "Here you go - make one like this!" They have copied the physical appearance quite well even down to the "12.9" stamping. To quote from the Chinese boffins: "12.9??? - what does that mean?? Oh well the sample has it so we had had better make it like that too!! I'm actually quite surprised it has FFH stamped on it. I would normally have expected something more like CAMAX, KAMA or maybe even XAMAK!!

Note from memory ARP have some good information on their website about spotting fakes.
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1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
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2015 Honda City 5spd.
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PostPost by: Elan45 » Fri Jul 05, 2019 3:44 pm

There must not be a single metallurgist in all of china!!! I'e not had a problem w/ ARP bolts in USA. Most ARP rod bolts are reduced size 12 point heads, not hex and certainly not w/ metric strength codes.

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PostPost by: Donels » Fri Jul 05, 2019 4:52 pm

The ones I removed were kamax, so probably original bolts. I am tempted to refit them.

Latest update from Burton's are they think it?s a recent batch problem but are going back down the supply chain to make certain. They are sending me a new set.

But I do have to question Burton on what they?re selling. Their standard bolts for twin cams are for 35 ft lbs torque loading, according to the web site, where Lotus quote 45 ft lbs. Either they are not suitable for twin cams or they are Ok for 45 ft lbs.
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PostPost by: el-saturn » Fri Jul 05, 2019 5:08 pm

just following this topic and worry with you fellas!! ... such a vital part!! i hope and have faith that my arp's are sooo good, that they easily take the loads and can be tightened/used a bunch of times - in my case actual fatigue is not a criteria (mileage) - but burton is stretching pretty far, if they have to sell such important bits and know nothing of their properties -- scary! Sandy i otherwise like burton
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PostPost by: Elan45 » Fri Jul 05, 2019 10:09 pm

This is a bit scary for me as I have a 1300 BDH motor to build and I had considered buying springs from Burton, as well as other critical components. Maybe I don't want to trust their quality control. A broken valve spring in a 16 valve BD engine is usually disastrous.

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