Lotus Elan

Faulty Con-rod bolts

PostPost by: StressCraxx » Sat Jul 06, 2019 12:40 am

Donels wrote: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.


The difference in bolt stretch between 35 and 45ft/lbs is pretty significant. The tension(stretch) must be significantly greater than the cyclic loads of rod reversal. Not enough margin between cyclic load and stretch will eventually cause the bolt to loosen and fail from fatigue.

A bolt stretch gauge is more precise than a torque wrench. I have found with ARP rod bolts (they recommend 50-55ft/lbs) are very consistent with torque on oiled threads vs a stretch gauge. The ARP rod bolts are 8740 alloy which has a much higher tensile and yield strength than the OE bolts, hence the higher recommended torque.

I would not re-use OE rod bolts that have been used in a running engine. YMMV.

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Dan Wise
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PostPost by: 2cams70 » Sat Jul 06, 2019 3:55 am

rgh0 wrote: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.

cheers
Rohan


I think I've identified the manufacturer as the Fu-King bolts company in China! :lol:

I disagree on not considering re-using the original bolts if they are in good condition and you have fair idea of the history. Of course it's best to replace with ARP bolts but really the more you play around with these engines the more you come to realize how clever the original designers of the Kent series engines were. OE is very often best despite the claims of the aftermarket especially if the intention for the engine is just to be in a normal road state of tune and not a race engine. There's lots of little subtle differences in design of parts across the series which makes you come to realize that Ford's engine designers were definitely A grade back in those days.
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PostPost by: JonB » Sat Jul 06, 2019 7:37 am

2cams70 wrote:I think I've identified the manufacturer as the Fu-King bolts company in China! :lol:


More like The "Fu-K U" Bolt Co., China if you ask me. Still, when you buy from Burton your contract is with them, not the maker, so it's at least encouraging that they are prepared to investigate the supply chain. On the other hand, their reputation is at stake here..
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PostPost by: 2cams70 » Sat Jul 06, 2019 10:24 am

JonB wrote:
2cams70 wrote:I think I've identified the manufacturer as the Fu-King bolts company in China! :lol:


More like The "Fu-K U" Bolt Co., China if you ask me. Still, when you buy from Burton your contract is with them, not the maker, so it's at least encouraging that they are prepared to investigate the supply chain. On the other hand, their reputation is at stake here..


Ha ha! Well Fu-K U2 :lol: Burtons probably placed an order on April 1st for these. I'll bet there were lots of Chinese whispers happening when they did!
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PostPost by: nmauduit » Sat Jul 06, 2019 11:55 am

it's not as easy as it seems to keep an up-to-date reliable supplier list.

I avoid getting any critical parts from B... I consider them as a supermarket, not always bad but the attention to detail I need for my pride and joy: for engine parts I usually go to QED; TTR is also a good source for high specs parts, race proven in many instances (no affiliations with either).
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PostPost by: el-saturn » Sat Jul 06, 2019 1:25 pm

i could also easily resist getting a waterpump assembly off of them - they have all the accralite sizes on stock and (ef) the thicker thrust washers thad qed doesnt have! sandy
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PostPost by: 2cams70 » Sat Jul 06, 2019 1:41 pm

nmauduit wrote:I avoid getting any critical parts from B... I consider them as a supermarket, not always bad but the attention to detail I need for my pride and joy: for engine parts I usually go to QED; TTR is also a good source for high specs parts, race proven in many instances (no affiliations with either).


I agree with what's been said that it's difficult for Burtons, QED et al to have full control over all of their suppliers. The test for me is always how they react to the situation when there is an issue. The bad ones will try and fob you off even though they know their customer base is quite knowledgeable as you generally have to be to be able to do work on engines.

As has already been said also it always pays to stick with brand names and you can generally be assured that when brand names are stocked by Burtons, QED et. al they aren't counterfeit.

I would not in my right mind ever purchase the QED branded cylinder head bolts for example when you can purchase ARP from other sources (ARP head bolts aren't stocked by either Burtons or QED)

I once bought a new shortened jackshaft from QED. It wasn't in a branded box but I saw "KC" stamped on the front face and assumed "Kent Cams" and quality. Well on the first one I bought the front journal had not had a final linish after the oil groove had been cut. This left it with very, very small raised burr around the groove. Not knowing this of course when I tried to install the shaft it dug big score marks in the front bearing. Bugger.
I explained this to QED sent the old one back and they sent a replacement no problem. When the replacement arrived I promptly linished the front journal learning from last time and installed it having had another set of cam bearings installed in the meantime. Great I thought.
I then decided to check the end float. I'd installed a new steel thrust plate (they are a couple of thou thicker than the standard item to reduce the end float for better ignition timing control) and lo and behold I find the shaft having a slight bind against the plate in one position. Measuring with feeler gauges I discovered with this jack shaft that the front mounting flange had a .002" wobble hence the binding (The steel thrust plate reduces the end float to around .002" from the around .006" with the standard sintered item) Bugger again!
At this point I told QED I wanted a refund and I was just going to obtain a secondhand OE jackshaft and shorten it. QED were very apologetic about things and gave me a full refund no problem. I have no issues with QED.

Surprise, surprise the end of the story is that I got my hands on an OE jackshaft shortened and it fitted perfectly no problem. No front end wobble whatsoever and perfect .002" end float.
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PostPost by: el-saturn » Sat Jul 06, 2019 9:37 pm

b4 we all have ta go ta bed: ARP seems to pass even the highest levels of scrutiny: we need U scrutineers, sandy
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PostPost by: Donels » Sun Jul 07, 2019 4:33 pm

Update on the bolts. I complained to Burton Thursday pm and they rang me back to confirm that they had found the issue on some stock. Friday they contacted me to say that a new set was on its way and they will keep me advised of their investigation. Saturday morning the bolts arrived, so they have been very proactive.

The bolts looked fine, so fitted and torqued to 45 ft lbs with no problem. Checked tightened this evening and no relaxation so I am happy they’re Ok. Why 45 ft lbs and not 35 ft lbs? Well the original bolts are 12.9 and these are marked 12.9 so they should be equivalent to original, and if they’re not I want to know about it.

I gave some thought to the torque tightening figure and I think I can explain it.

The Ford 1600 applications of the block are limited to 6,000 rpm whereas Lotus is 6,500 - 6,750.
The tensile loading in the bolts has to be greater than the cyclic loading from the piston being decelerated to zero, otherwise the bolts will fail from fatigue.
The cyclic loading stresses for Lotus applications is therefore much higher requiring a higher tensile load, hence 45 ft lbs and stronger bolts to avoid a fatigue failure, assuming similar weight pistons to Ford.
If you have used 35 ft lbs then you could have a failure if you use greater than 6,000 rpm as the bolts could fatigue.
How quickly this will occur depends upon how high you rev the engine, but as a guide I did the following calculation.

The cyclic stress threshold for steels is 10 to the eighth, ie 100 million cycles.
At 6500 rpm this will be reached in 15,000 minutes or 250 hours.

So you’re probably going to be Ok unless you do track days, sprints, etc.

Which comes to the reuse of original bolts. If you know they were tightened correctly and the engine has never been over reved then theoretically they are fine to reuse. The difficulty is knowing the above, hence fit new if you don’t know the history.

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PostPost by: 2cams70 » Mon Jul 08, 2019 12:16 am

Personally if it were me given the experience I'd just had I'd still ditch them. Maybe I'd consider using them for hanging posters on the wall but certainly not in an engine. From Burtons these bolts are 4.20 GBP each versus 9.42 GBP each for the ARPs. In the context of the cost of engine rebuild the incremental price is insignificant. It is interesting to note that the picture Burtons have on their website for this bolt is the original Kamax one. If in fact they are supplying something else this is really something to complain about.They even say these bolts are suitable for BDAs for goodness sake!!

It would be interesting to do a side by side stretch comparison with an original bolt - i.e Torque one up to a specific figure and measure the stretch with a stretch gauge and do the same with an original bolt and compare. Regardless of the result I'd still ditch them though!!

el-saturn wrote:b4 we all have ta go ta bed: ARP seems to pass even the highest levels of scrutiny: we need U scrutineers, sandy


Whilst ARP products themselves are excellent I do wonder sometimes about the torque specs they recommend. Sometimes even the stretch figures for conrod bolts seem a bit inconsistent across the different grades and sometimes what the connecting rod manufacturer recommends for ARP bolts conflicts with what ARP recommends.

As far as those Burtons bolts are concerned i still have visions in my head of those boffins in China mulling over the Kamax sample bolt. 12.9?? Aaah!! must be Englishman lucky number. We have 888 they have 12.9 - must put on bolt!! must put!! must put!! Sorry I do have a bit of Chinese heritage so I'm well able to take the piss without the political correctness brigade that exists these days trying to take me down!!
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PostPost by: el-saturn » Mon Jul 08, 2019 5:27 am

i can only get above 4000rpm if i'm out in the prarie, as the swiss hate the "sound of music" - this old english lady/teacher (next doors) called the police "on by behalf", asked her landlord about me (and my neighbor: TC seven) .......... he likes our cars ..................... so she moved to another location and we feel free again sandy
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PostPost by: 2cams70 » Mon Jul 08, 2019 5:39 am

el-saturn wrote:i can only get above 4000rpm if i'm out in the prarie, as the swiss hate the "sound of music" - this old english lady/teacher (next doors) called the police "on by behalf", asked her landlord about me (and my neighbor: TC seven) .......... he likes our cars ..................... so she moved to another location and we feel free again sandy


Sandy you should have swapped the sound of the TC with the sound of some full on Swiss yodeling. That way she would have welcomed back the sound of the TC no problem!!
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