Broken camshaft

[GreekS1]

Hello all,

I was competing at the Historic Acropolis rally this weekend. All was going well and for three days we enjoyed the rally in magnificent scenery and around 800Kms, On Sunday we where returning to Athens via the main motorway to do our final regularity (no 40!!!) of the rally and finish under the Acropolis in Athens. Suddenly, while doing around 80mph, I heard a ping like metal breaking and lost all compresson!

After checking the fuel pump, electronic ignition and that nothing visually wrong with the engine I called for the recovery tuck. Yesterday we opened up the cam cover to discover a brocken inlet camshaft! It was sliced clean through towards the front of the engine. We have checked the vlaves and only one seems to be bent. We will now remove the head to check for further damage..

As I didnt rebuilt the engine I dont know what has been done to it so my question is where to get my parts form?
Im leaning towards QED. Should I uprate the cams or get standard ones? Also can anyone tell me if htese cams aree standard? Im attaching pictures.

I am really in the dark here so any recomendations and ideas are very welcome.

PS. to top off the bad luck, my bonnet flew off while on the recovery truck and has been pretty bashed up...Apperently the spring holding it down at the front also broke!

Thank you

Vassilis

[rgh0]

Not an unknown problem though its more usual on the exhaust side. Very rare in a standard engine and more common in one with modified valve train with higher lift cams and / or stiffer springs and running at higher revs.

The modification is to fit a long bolt that goes into the cam past the first bearing. The bolt is drilled down the centre to provide a feed to the bearings. Most people such as QED who provide modified cams can also do the required drilling and tapping and provide the specialised longer bolt.

An alternative is a steel cam which is stronger than the standard cast iron one but that introduces its own set of problems with galling between the cam and follower especially in a modified engine when you will also certainly be using steel followers.

You will have probably bent more than one valve but you will see how much damage when you pull the head.

QED are a good supplier of parts especially if building an uprated engine.

cheers
Rohan

[john.p.clegg]

"The modification is to fit a long bolt that goes into the cam past the first bearing. The bolt is drilled down the centre to provide a feed to the bearings. Most people such as QED who provide modified cams can also do the required drilling and tapping and provide the specialised longer bolt."

Does it have to be drilled at a radius also?

John

[rgh0]

Hi John

Yes a radius hole also from the centre hole to feed oil from the front bearing into the bolt and the cam that then feeds the rest of the cam bearings
Somewhere I have posted a photo of the bolt before

found it

cheers
Rohan

[john.p.clegg]

Ooooeeerr...that looks like it should be done in-situ?...and a once only job?...and be careful of the swarf?

John

[rgh0]

Hi John
If you look closely you will see the threads have been removed in the radius hole area so that the bolt radius hole does not need line up exactly with the hole in the cam as oil can feed around the outside of the bolt until it finds the oil hole

I have made them without doing this by grinding the washer on the cam end until the 2 holes line up when you torque the bolt.

cheers
Rohan

[john.p.clegg]

Nice.

John

[promotor]

That's a lot of thread tapping to do to get the long bolt in!

Rohan you mention that QED offer this service to modify cams have you had experience of this recently as when I asked them they almost seemed to be unaware of the process!

[rgh0]

I have not talked to QED for many years about it. Since they stopped building engines they may have forgotten about it! They really should not be selling high lift cams without doing this mod or at least recommending to customers they do it as a high lift cast iron cam is not really fit for purpose without it.

cheers
Rohan

[promotor]

Can I ask what dimension the shank of the bolt is? And is it best to use a fine or course thread?

Also, what strength bolts do you recommend? The strongest I can find? Or S,V,X?

Cheers.

[rgh0]

There is a photo above in this thread of a spare bolt I have posted. Same size and UNF thread as original bolt just longer to reach further into the cam to the rear of the first bearing. Normal Grade 5 ( 3 radial lines) high tensile bolts appear to be fine in the application. You cant really torque it to full grade 8 tension capability in an iron casting like the cam I think and I torque to the standard recommended torque by lotus for the original grade 5 cam bolt. I have also got a set of high tensile studs and nuts from John McCoy for a couple of the cams he supplied me at one time these would enable you to get some more tension as not trying to turn the thread in the cast iron under load. The aim of the long bolt is to keep the cast iron at the oil groove in the cam in compression so it does not crack you are not really relying much on the bending strength of the bolt itself.

cheers
Rohan

[promotor]

Excellent info as always Rohan - thank you very much.

[SJ Lambert]

Gonna do this on my old L1 cams shortly.

[Foxie]

I was interested in getting the "long bolt" mod on the new QED 450 cams I was fitting a few weeks back, and contacted QED. Here is their reply:

Hello Sean
Not something we have ever offered in the 25+ years i have been here, sorry.
Simon Lea
Sales Director
QED Motor Sport Ltd

[rgh0]

It really surprises me that QED don't do the long bolt mod on the high lift cams they sell and appear not to be aware of it. A high lift cam without it leaves you very vulnerable to a broken cam. My local cam grinder with 50 years experience doing twink cams (Clive Cams), Dave Bean and John McCoy certainly recommend it

Maybe its a USA originated thing ? I wonder how many racing twinks in the UK dont have it ? Maybe they all use steel cam blanks because their iron cams always broke ?

cheers
Rohan