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Daimler 15: stripped thread

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captain bobo
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Location: Kimbolton, Cambs

Daimler 15: stripped thread

Post by captain bobo »

Putting the head back on the block yesterday I was progressively tightening the head bolts towards 41 foot pounds. At 30, the rearmost head stud (that is threaded into the block) stripped the thread in the block. All the others tightened up okay.

What is the solution? Is there an engineering fix (hopefully a home visit from a company because I don't want to take the engine out)?

Why do jobs like putting the head back on (a job I've done so many time on different classic cars) sometimes go wrong? Aaaargh!
Best wishes, Dave B

Simon Hyslop

Re: Daimler 15: stripped thread

Post by Simon Hyslop »

Belonging to a club for another make which suffers from this problem regularly, I hope the following may be of use. I have been down this road several times in the past decades and, in ascending order of severity, here goes:

1) Fill with JB Weld then drill and tap out to normal size. A large amount of prayer or incantations may be required with this but there are rare cases where it can work,
2) Heicoil the existing thread, or ReCoil or your chosen make, then replace with a standard sized thread.
3) Drill out to take an oversize based stud. This may have to be made but oversize base studs are available for some makes and may match what is needed.
3) Drill out to take a heicoil of the size to fit an oversize based stud. This may be hard to believe, but it is the recommended method for fixing this problem on a marque that is as old as the industry.

Which one you, or a company, decide to take will depend on the state of the deck. The problem with rearmost studs can be access. I had this recently with an Austin Heavy 12 and it was a real beggar to get into. It's a bit like quartering model locomotive wheels, you need to be at 90 degrees, not 89 or 91 but 90. Using the head as a guide to ensure the drill is at right angles helps but extra long drills are usually needed. Hope this is of use in at least formulating a plan.

Rolf B.
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Re: Daimler 15: stripped thread

Post by Rolf B. »

Hi Dave,
when fitting the Helicoil I recommend to use a thread sealing (not a thread glue) like from Loctite to seal the thread in the motor block to the Helicoil and then between the Helicoil and the thread of the stud. This is to prevent penetrating cooling liquid from the water jacket of the block into the cylinder head. We had this problem at the engine of the Daimler 15 after a full rebuild was done.
Between the thread of the block to the thread of the Helicoil and between the thread of the Helicoil to the thread of the stud are micro gaps which allows the water coming up because the header tank of the radiator is higher than the cylinder head. Even though there's no pressure in the cooling system this little hydrostatic pressure coming from the difference of hights allows the water running along the threads into the cylinderhead, exiting at the upper end of the stud at the thread where the washer and the nut is fitted.
Regards Rolf

Petelang
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Re: Daimler 15: stripped thread

Post by Petelang »

Totally agree Rolf, I had the same problem and it filled the sump overnight with coolant. I couldn't think where it was coming from but stood over the engine with rocker cover off and watched a tiny blob of antifreeze appear around two studs. Extremely slow, but stood for two days it produced a considerable amount.
Be very very careful with the two studs on the distributor side of the block as this is where the block face cracked on mine, neccsitating a total strip and block stitching.
Peter Langridge
Cloud Nine Classic Weddings, Nottingham.

Chris_R
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Re: Daimler 15: stripped thread

Post by Chris_R »

On another make of car I have used the helicoil solution to repair an exhaust manifold stud in the cylinder head. On this car the hole actually penetrates the water jacket and the stud usually seals that. I used a thread locker when inserting the helicoil which has worked very well, took the stud and there have been no leaks.

Stan Thomas
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Re: Daimler 15: stripped thread

Post by Stan Thomas »

Hi Captain BoBo,

Before you slash your wrists, check if the hole in the block actually goes into the water jacket - as normally they are specifically designed not to do so for the very purpose of coolant seapage which would otherwise occur.

By far Helicoil is the (only) answer. You cab buy a kit for the requisite size quite cheaply which comes with the correct tapping drill and tap. A good tip is to get someone with a "good eye" to ensure you hold the drill at right angles, or better still, see if the Helicoil tap will pass through the cylinder head stud hole. Iif it does, slip the head back on the block and use the relevant hole as a guide for the drill.

Let us know how you get on.

Stan.

P.S.
If you had a sleeve valve, you would not have to faff about with silly cylinder head bolts!

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captain bobo
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Joined: Tue Feb 09, 2016 7:32 pm
Location: Kimbolton, Cambs

Re: Daimler 15: stripped thread

Post by captain bobo »

Thank you all for your comments. As a novice researching "helicoil" I see that there are things called "externally threaded inserts" that also, of course, have internal threads for the stud.

Can anyone comment about the suitability or merits of the external threaded inserts as compared to the helicoil "coil spring" type of insert?

Ignorance, in this case, is not bliss!
Best wishes, Dave B

NickDeAth
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Re: Daimler 15: stripped thread

Post by NickDeAth »

As I read it "an externally threaded insert " would only be a generic name for the trade name "Helicoil". In the same way that a lot of people call worm drive hose clips "Jubilee" clips.

Nick
"Nick - do you think you will ever put that old car back together again?"

Rolf B.
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Location: 68309 Mannheim, Germany

Re: Daimler 15: stripped thread

Post by Rolf B. »

The threads in the blocks of Daimler 15 engines for the cylinderhead studs are ending in the water jacket of the block and are not threaded in blind holes as you can see at the attached photo.

Rolf
Attachments
engine block Daimler 15.pdf
(1.53 MiB) Downloaded 55 times

Chris_R
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Re: Daimler 15: stripped thread

Post by Chris_R »

First, as has been said, Helicoil is a brand name. It's actually Helicoil® Sav-a-Thread®, the product name. I think it was the original thread repair product and others have copied the idea and sell their own versions. What the difference is in quality I don't know. One of things I have noticed is that the Helicoil brand does have different length thread inserts whereas most of the other that I have seen don't. I would think for this application that thread length is important so getting the right length insert will be needed.
Second, you can buy drill attachments that ensure you drill at exactly 90 degrees, provided that is of course that there is space above hole to allow you to drill directly. If not you will need to look at buying a right angle drill attachment. Not sure if you can use the drill attachment to ensure correct drilling on a 90 degree attachment or not.

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