pistons and valves contact

[Hawksfield]

John
Sorry to hear the bad news after all you have done.
Hope you get someone to help you diagnose the initial failure .
You really need to have assistance.

John

[billwill]

Sigh!

[rgh0]

Extremely frustrating when something like this happens and sorry that the build did not work out

Something went wrong to impose excessive chain load to break it. You need to understand that root cause. Unusual also to bend a cam as they are normally cast iron and break rather than bend unless you have a steel replacement cam ?

[2cams70]

Thanks for providing an update for some lessons learned unlike most people who when faced with a situation like this would rather choose to not say anything and bury their mistakes.

At least you can take some solace that your Greyhound is happy having received something positive from the experience.

[Phil.C60]

I too am sorry to hear that it's all gone wrong for you. I would gently suggest that you take a step back at this point and not just dive in and rip it apart. The engine is obviously going to have to come out and be completely stripped, but I can't emphasise strongly enough that that needs to be by, or with the assistance of, someone who knows exactly what they are doing and can examine everything as it comes apart, piece by piece. It's the only way to be absolutely sure that it doesn't happen again. I would suggest even more gently having followed this thread that I'm not sure you are able to do this yourself. By all means take the engine out, but after that please seek some assistance. From your description of the damage unfortunately there is likely to be considerable cost involved. Once again I'm really sorry that you find yourself in this position. Regards Phil

[checkrail]

Having had a closer look at the damage, the cam is not bent but has snapped in two leaving the sprocket end in the groove twisted out of line. This is what caused the locating corner of the head to break away.
The sprocket bolt was compleatly undone, the sprocket still attached to the broken chain, I presume that I hadn't tightened the bolt enough.
I just hope the head is repairable by a specialist. The cam is a QED 420

John

[Spyder fan]

Having had a closer look at the damage, the cam is not bent but has snapped in two leaving the sprocket end in the groove twisted out of line. This is what caused the locating corner of the head to break away.
The sprocket bolt was compleatly undone, the sprocket still attached to the broken chain, I presume that I hadn't tightened the bolt enough.
I just hope the head is repairable by a specialist. The cam is a QED 420

John

John,
Really sorry to hear about your woes with the engine, may I ask if the Q420 cams were already fitted to your head prior to your recent works or did you add them? I recently sold an engine with Q420 cams and the piston crowns required quite a bit of machining so that there was no contact between pistons and valves. They were new Accralite pistons, so not sure if standard pistons would need a bit of machining, but Rohan would know.

Tough luck whatever!

[checkrail]

yes Q420 cams were aiready fitted

John

[h20hamelan]

And did you use the associated 55 springs, or stock valve springs

[gjz30075]

Is it also possible that the chain is a 'two piece', ie, requiring one to fit a link which, I think, is
directional?

[512BB]

I am sorry now, that there just was not enough time John, when I was up your way, to pop in and see you, but it was to late in the day when you phoned, shame.

By coincidence, on that day, I was with a mate who had recently shown me a twincam head that he had had welded. He told me that it came from a car that had been in an accident, and the whole of the timing chest was smashed in. Well, I looked and looked, but I could see no evidence of ANY damage, or indeed, of any welding.

On seeing that, I took 5 ali diff covers to this guy, that needed a bit of a touch up. He did them while I waited !

If the head needs a bit of a touch up John, you have my number.

All the best,

Leslie

[alan.barker]

Hi John,
i feel sorry for you. Try to rest zen and the boys here on the forum will help you through this bad moment.
Most of us have learnt by our mistakes over the years.
You have a very nice offer from Leslie with his knowledge on Twinks.
Good luck
Alan

[checkrail]

Thanks for the symphathy, I have been contacted by Phil on the South Coast offering me loads of help and advice on all aspects of the rebuild.
Regarding the head damage I am taking it to the Cylinder Head Shop which luckily is not too far away, hopefully with a positive result

Regards John

[rgh0]

Hi John

I presume the cylinderhead shop will do the repair welding and machining and do a complete check of the head and replace any damaged components to bring it back to specification tolerances. You need to get them to hardness test the head to check that its worth spending the money on repairing

What are you planning to do on the block to check for potential damage?

I personally would do the following after this sort of incident by doing a total strip down and mesurement of all block components. While visual inspection will tell you a lot, precision measuring equipment and die pentrant cracking testing is really required. When dismantling items ensure they are properly labeled so they can go back precisely where they came from it reused

Key checks to make where damage is likely in this sort of incident below but every components needs close examination as unexpected things can happen.

1. Check the pistons for contact damage as impact with a valve can cause cracking or distortion. If uncertain replace the pistons
2. Check the rods for straightness and any distortion on the journals due to impact damage.
3. Check the crank for cracking and straightness. Check the crank sprocket for damage
4. Check the jackshaft and all its components for any damage suffered when the chain failed.
5. Check the tensioner sprocket for damage when the chain failed.
6. I would defintiely replace the big end bearings and potentially the main bearings also

Happy to provide advice on any issues found when doing all of this, but you really need to get up to speed on transferring photos from you camera so you can post them here.

cheers
Rohan

[checkrail]

Good news, The head is off again, there is no sign of any piston/valve contact.
Hopefully valve spring compressor will arrive tomorrow , looking at the PO receipts the correct Q55 valve springs are fitted.

John