LOTs of US head bolts

[2cams70]

I doubt it has anything to do with the bolt metallurgy. The OP has two suppliers of bolt (QED and OEM Lotus) both of which have broken in service.

[alan.barker]

Correct me if i'm wrong but i don't think any original ?quipement bolts have broken . Only the alternative bolts.
Alan

[Quart Meg Miles]

In the 2007 rebuild the block, after relining, was measured flat (not sure if it been ground) and the head was skimmed after all its rework. I will check the head thickness to make sure it isn't bevelled and I need a longer stick to check the flatness of everything. I'm the only person ever to rebuild the engine so there's nothing but oil and Wellseal. I've cleaned the oil out of all the holes but will go round again with a solvent and wind a tap down too.

Thanks for all your help, chaps. I hadn't realised that water had mixed with the oil, didn't show on the dipstick, so I'm going to need all new bearings. Some of the main shells are worn by 0.001" or more and the conrod shells by nearly as much. Guess the cams will be gone too so it's all rather depressing and I haven't stripped the head yet.

[alan.barker]

Cheer up,
Look on the bright side the Engine will be on top form ready for the Summer and lots of driving
I've just changed the clutch on my Sprint and "Little Lo" is up and running again I even fitted a new starter ring and got the flywheel skimmed. Next time you see Miles Wilkins who knows my Sprint very well you can say it's still being driven. Lagoon Blue fhc that Mrs Best used to own (he changed the chassis).
Alan

[Quart Meg Miles]

Correct me if i'm wrong but i don't think any original ?quipement bolts have broken . Only the alternative bolts.
Alan

This is correct, all the broken bolts were the new ones of uncertain parentage and they are not the ultra thin type. I expect I changed the bolts at the two previous block borings so there won't be any originals around. This is a high mileage engine, only the major castings are original (except rods which are 125E)!

[2cams70]

In your earlier post when you said "Wilkins supplied S/H ones" I was assuming that meant second hand Lotus OEM ones and that these had broken also. If in fact the bolts that broke were all from the same source then yes that does point to there being an issue with the bolts themselves.

On rebuild I'd suggest sourcing the ARP bolts. The bolts don't require any enlargement of the holes in the head and in my opinion are better than the studs on a road engine at least. The bolts have the same torque figure as standard OEM bolts whereas the studs require a higher torque. Ford would have originally designed the threads in the block and deck reinforcement to suit the original torque figure. More "spring" in the bolts I believe would also help to maintain clamping force in a road engine subject to many cold/hot temperature cycles (just my theory at least)

The cost of a set of ARP bolts is about the same as a set of new bolts from other sources so they are an inexpensive investment.

[Quart Meg Miles]

Things are being confused by the terms being used; let me restate.

I have no "original" bolts. The earliest ones in my possession are the "suspect" ones from the 2007 rebuild and all four breakages were from this batch.

Wilkins s/h bolts were taken out of customer engines when he fitted new bolts in them, and they were just lying around. The first pair are different to the 2007 bolts and are nicely tapered at the shank step and have rolled threads; the second pair, provided this year, are of similar design and marked GKN. I don't have the original pair though but earlier photo shows they broke where the turning starts.

I have cleaned the threads in the block with a "plug" or No 2 tap (cost me ?1) and kept a rough note of the depth it went each time, between 3 and 5 threads from the top. Combined with the variation in bolt lengths and compared to the head thickness (see below) it is possible that one or more might have "bottomed", we are talking just a few millimeters clearance in all cases and I will, tomorrow, formally measure the depth available in each hole using a single bolt. The tap has a taper at the end of the thread so who knows what stops it.

I have, at last, received new QED bolts and washers and, as SteveH described on 27 Feb, they have small fillets under the head and also tapered shank changes but are turned threads (I believe; there is a hole in the end of the shank to support this operation). As Steve notes, the washers still have sharp edges and I believe that the underside of the bolt head is slightly tapered and also has a serious chamfer to the sides, so there isn't a huge amount of bearing surface.

s/h GKN, s/h not known, 2007 failure batch, 2017 QED

Difference between rolled threads (left two) and turned?

Some of the bolt length difference is an illusion as they are levelled at the top of the head flange, which varies in its thickness. There is a similar difference between individual bolts, in the 2007 set at least.

The head thickness, measured by vernier caliper as close to the corner bolt holes as possible, is 116.5 mm ? 0.1 mm. (?, whatever it comes up as on your screen is the maximum deviation). What is the original thickness of a head? Also does anyone know how much a bolt stretches after 65 ft-lb tightening?

I have just purchased a two foot rule to check out all the flatness and twist features of head and block which I will attempt soon.

Any comments on observations will be gratefully received, and any answers. I will investigate the ARP type and might have to discuss matters with QED, who only do studs.

[2cams70]

So for clarification "GKN" bolts are breaking too? Is that correct?

GKN are original Lotus bolts. GKN is the OE supplier.

[alan.barker]

Well i hope you find the cause.
I have worked on Twin Cams since 1973 when i bought a 1968 Cortina Twin Cam and never seen this problem before. All the Twin Cams have been with the 6 bolt crank that i have worked on.
Do you think the Spot Faces on the head for the bolt heads need a light resurface to be 100%.
Serveral times Rohan has spoken about hardness of heads, perhaps the head on your car is soft.
Alan

[2cams70]

ARP bolts are available from Tony Ingram. See link below:

http://www.lotus7.com/ARP_fasteners.html

As to other causes of the bolts breaking:

Is it a 1500 or 1600 block? If it's a 1600 block it may have been decked to achieve 1500 block height and in doing so the depth of the head bolt threads reduced.

Were the threads only minimally lubricated prior to assembly? If over lubricated the bolt may have hydraulically locked in it's thread leading to an incorrect tightening torque.

Rapidly running out of other ideas now !

[rgh0]

The head shown in the photo looks good with little bolt recession so it is probably not soft. The bolts are relatively flexible and a small amount of misalignment between the blot thread in the block and the top surface should not be a problem. Original standard / SE head thickness is 4.640 inchs / 117.86 mm. Sprint Heads were originally 4.600 / 116.84 mm. I dont believe the bolts length ( or the cam timing marks for that matter) changed with the introduction of the sprint heads so with a head at 116.5mm you should still have clearance from bolts bottoming out unless the threads have been damaged at the bottom or the block has been skimmed signficantly also.

I would not use head bolts with turned threads as there is to much risk of a crack forming at the base of the threads. I would use good second hand ones if standard rolled thread bolts cannot be sourced but preferably I always use ARP bolts or studs now.

cheers
Rohan

[steveh]

If i had known ARP bolts were available i would have probably bought them , i avoided the ARP studs because of the stud to hole clearance issue.
Mine were replaced because they were the thin diameter shank ones , 2 had waisted through stretching.

Rolled threads are stronger but i would expect nowadays with CNC lathes and indexable insert tooling the thread form / root radius should be perfect with no flaws , i think some reassurance is needed from QED that their bolts are up to the job . From a quick research i see ARP bolts are tread rolled after hardening [ quoted as giving 10x the fatigue strength] , qed bolts i would expect to be machined soft then heat treated .

If anyone can quote them it would be good to know the ARP product codes for both the bolts and studs .

[el-saturn]

rolled threads are always MUCH better: its the uncut flowlines and the material compression during the production process which make the big differences. handcut threads are for static applications! sandy

[Quart Meg Miles]

Thanks again for responses!

2cams70: Pay attention, please. Only the new bolts in 2007 broke, the GKNs were offered by Wilkins after the most recent breakages. I am seriously considering ARPs and will check out your link, thankyou.

Mine's a 4-bolt serial LP2447 so no decking needed.
I'm going to try hydraulic'ing a bolt but I don't think it will as the oil can escape up the thread and then into the head passage round the bolt. Worth trying as I tend to be generous with oil.

Wilkins, who I spoke to today, has never had a bolt break, ever, and he's only ever used one set of QEDs and found that they wouldn't go through the head of a 4-bolt (mine do) but they did in a 6-bolt.

alan: It may have a soft head (me too) but Rohan thinks not. If anything it is a little "dished" round the holes where the washers have also dished and settled in. I'll have close look before cleaning up for assembly

Rohan: Thanks for data, I suspected I had Sprint compression! The GKN bolts were at least 2 mm shorter in shank than the QED and 2007 set, so the bolts seem to getting longer as the head gets thinner! Today I measured every bolt hole with a single bolt and there was 5 mm variation. The shortest hole (No 2) was nearly 3 mm shorter than average but the 2007 bolt which had been there theoretically still had 2 mm left for the washer and bolt stretch (and hadn't broken). Marginal, I would say.

I think I will return the QEDs and as they seem to be the only source of bearing shells now I can probably strike a deal. First I need to locate a s/h set of rolled thread bolts or new ARPs.

Thanks all.

[Quart Meg Miles]

The hydraulic bolt lock syndrome appears to be an urban myth, at least on my car (read below). Ironically the supplier of my s/h head bolts, ordered today, has also put it forward as one of the three failure mechanisms, the other two being a build up of rust down the hole causing bottoming and dishing of the head/washer system effectively lengthening the bolt,

I poured oil down hole no 6 (in which the thread had snapped on the recent breakage) leaving 25 mm (1 inch) of air above it to the deck, then screwed one of the 2007 bolts into it by hand. I felt it reach the oil but could still turn the bolt easily by hand and oil appeared out of the top of the hole, having travelled round the thread. Eventually the bolt bottomed at its measured depth of 28 mm. I have computed that the space around the narrow 88 mm of the bolt shank in the head is enough to absorb the entire 28 mm depth of the bolt hole which might be displaced if the hole was full of oil.

The s/h bolts, from ebay, are from a Lotus Cortina Mk II and I'm returning the QED bolts.