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Bit of a 'Headache' - Knackered Cylinder Head Diagnosis/Advice Requested


leelbuk

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Well I suppose even I thought it was too good to be true that my DIY single build had been running without hitch for as long as this! Even so, I'm still feeling lucky this didn't happen at some silly RPM and cause more serious damage though I'm looking for advice on how serious the damage actually is as, truth is, I'm a tad unsure.

 

Brief account of events:

 

I go for a drive one pleasant afternoon with a friend having there been no previous problems, strange noises or behaviour from any part of the car, including engine. All went well except for hitting a slightly large pothole in the road (was doing only 20MPH, no damage though felt one hell of a thump!). All still fine after this so carry on driving, a few spirited runs here and there but nothing crazy as the roads I was on wouldn't allow for it (was up cheddar gorge for those who know it, twisty, windy and uphil).

 

Was on my way back down hill, on engine braking most of the time in 3rd gear behind someone when I put the clutch down to change to 2nd and the car stalls - no weird noises, nothing preluding to this point, just the engine stalling. Thought it was a little odd and pulled over to the side of the road to restart the engine. Upon turn over I heard a metallic clunk to which both me and my friend turned to each other and had the "Ohh, that didn't sound good" look on our faces.

 

Stepped out of the car, whipped open the bonnet and after checking around found this under the spark plug cover: :(

 

1-S632.jpg

 

Exhaust cam pulley sheared right off and the belt chewed up a little. Naturally I'm already thinking something has jammed the exhaust cam, either by something getting in the way (stuck valve, bucket, shim) or the cam has seized however I was too angry with myself, the car, the 5 hours it took to recover etc to be able to think straight so the car was put on my driveway and there it stayed for 6 months.

 

The weather has since perked up and I've had long enough to work up the motivation to start taking things apart again - in doing so I quite quickly found the problem - No 1 bearing on exhaust cam looks to have been starved of oil and seized (my thought at least). Looks to have become quite hot and friction welded some of the aluminium head material onto the cam.

 

2-S362.jpg

 

3-S362.jpg

 

Now the bit I need advice on:

  1. Although none of the other cam journals show any sign of oil starvation and all of the rest of the valve-train functions normally I'm pretty sure that the head is unsalvageable at this point unless someone corrects me? Would like confirmation that no kind of repair is possible.
  2. Does anyone have any theories as to the cause so I can try to prevent it happening again? Possibly too much FIPG when fitting the bearing cap? Blockage in oil feed though cam? If a general oil pressure issue I would expect to see signs of it on more than 1 journal?
  3. As the rest of the engine is still ok, can I simply stick a second hand head on, get a new exhaust cam and off I go? (assuming something else in the bottom end isn't the answer to question 2 as a possible cause!). Any prudent measures to take before reassembling again?
  4. How much should I expect to pay for a second hand head? Advice on where to look for one?

As always, your advice is more than appreciated. I built the single as a DIY project so I could learn and I knew full well it could go wrong and would be expensive to fix - just want to make sure I learn from the mistakes!

Edited by leelbuk
numbers weren't showing (see edit history)
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Where is the oil actually fed to the cam journal? I can't tell from that pic. Is it something to do with the dogleg shaped slot in the bottom of the pic that looks like its full of something?

 

Unfortunately I would say the head is fubar'ed. :(

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It's fed through the cams themselves. Unfortunately it looks like the head is scrap, and I would presume so is the camshaft. I would say replace with a good second hand head.

 

I would also want to pull the sump off and give everything a thorough clean inside the block. 1- To make sure there isn't an underlying problem/blocked oilway that caused this. 2- To make sure that your oil system is now not full of swarf, dissasemble and clean it all.(Oil filter housing, sump strainer, etc..) And 3-fit a new oil pump. When you have it down to that stage it's then a case of where do you stop! If you have the money rebuild it, if you dont clean and re-assemble. At the very least it's probably worth changing the bearings for some uprated items, and the bolts for some ARP's. Good Luck!

 

You might be able to get some more life out of the head, i.e. Metal sprayed and re line bored. Or get a camshaft manufacturer to make you a cam with custom sized journals after having it bored. However it's going to be much cheaper to replace it!

Edited by TheTurtleshead (see edit history)
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Think the journals are fed via the cam itself from what I have read on the net so far.

 

Agreed it's rather wishful thinking the head might be salvageable so am prepared to replace the head but worried that I'll fit it and end up with the same thing happening again if I don't figure out what went wrong this time round.

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It's fed through the cams themselves. Unfortunately it looks like the head is scrap, and I would presume so is the camshaft. I would say replace with a good second hand head.

 

...

 

Thanks for the advice - sounds beyond DIY then for me as I haven't got a garage that would allow me to pull the engine or work on it whilst it's out. Don't suppose you can get at the strainer etc without pulling the engine?

Even if I could it might be worth throwing in the DIY towel for now and let one of the experienced engine builders on here rather than risk doing it myself and something going wrong again.

 

Still puzzled as to whether I did something wrong when I reassembled or whether there was another reason for oil not reaching the bearing. Is the most likely cause then that the oil feed through the cam was blocked?

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