Patchy's Fawlty Towers risk management. Enter at own risk

[StanTheMan]

So this morning I
Took the cams out
Checked the lifters
Took q best guess on the cam tops
Tightened the head just a fraction
Cleaned the cam sprockets
And made sure they were correctly fittted
Checked the cam belt rollers all good
Put it all together again

She was blowing smoke in a big way




Beer time.


It seems to be reducing..... come back tomorrow. But the noise is still there

[93_Clubman]

Took a best guess on the cam tops

I'm assuming, given a 27 yo car, they were already mixed-up, ie not in the correct place according to their factory marking? See here: http://ww.w.mx5cartalk.com/forum/viewto ... 57&t=73204
Re the noise, given so much clatter, could the belt tensioner be rattling?
viewtopic.php?style=3&f=29&t=47234

[StanTheMan]

Belt tensioner are only about 18mnth old. Maybe 7 or 8 k km. Of course possible but so hard to tell. Checked for tightness & they seem fine. I mean I checked them by hand how they roll. High rpm could be another story. They were fine before I took the head off.

Just courious why it would start blowing smoke after 120km?

The cams were tightened in the correct sequence .

[93_Clubman]

Re smoke, when checking HLAs perhaps some oil got past.

Belt tensioner spring is what I was suggesting might be rattling.

Might have misunderstood your post, but thought there was uncertainty about cam caps being in the right location:

Here's an E2 exhaust cap. The top of the E points to the front of the engine. The arrow cast just above it is correct in this case but it's not always so. The 3-10 above that is meaningless unless you wrote down all those numbers beforehand.

[StanTheMan]

Yes I got that
Caps are numerically arranged I swapped direction on some of them as there seemed a visually better fit. As in better coverage of the cam. No cam surface visible when looking from top down. Didn't make any difference. When I put the caps on originally they were not in order. Some arrows facing different directions. But all intake caps & exit caps were on the correct side.

Mine have "I" & "E" stamped on them as well.

Currently they are numerically arranged but on the exit arrow is facing the opposite direction.

[StanTheMan]

Re smoke, when checking HLAs perhaps some oil got past.

Belt tensioner spring is what I was suggesting might be rattling.

Ohhhhhh the spring will check that.

[StanTheMan]

Not the spring

[StanTheMan]

Could it be the pistons hitting the head? But then it would have self distruckted by now I would assume. The pistons clear the head by & valves turning manual
Total reduction is
0.75 mm by shaving
0.60 mm with extra thin head gasket
Total 1.35mm

I keep getting paranoid but I would assume any interference the engine would havedestroyed itself by now.right?

[manga_blue]

Noise may be HLA oil starvation. It's a bit complicated but I'll try to explain.

There's a ring groove around each HLA. Its purpose is to form a pathway for pressurised oil to get from the oil gallery in the head into the inner workings of the HLA. When the HLA is at rest at the top of its stroke (i.e. when the valve is shut) this ring groove should sit adjacent to an oiling hole in the HLA bore in the head. This is the situation for most of the cam cycle since the valve is more often shut than open, giving the HLA the best opportunity to be replenished with oil. As an HLA becomes worn it tends to lose more oil on each stroke and so this replenishment becomes much more critical.

Sticking HLAs tend to tick or clatter mostly at low rpm and cold. Oil starved HLAs tend to make a thrashing sound mostly at high rpm and hot.

Aftermarket cams with higher lift tend to have a smaller base circle diameter (BCD) than standard cams. This raises the " at rest" position of the groove in the HLAs by the difference in the BCDs between stock and aftermarket. Anything more than a 1 mm decrease in BCD is likely to raise the "at rest" position of the groove to somewhere higher than oiling hole. In consequence the HLA is only re-oiled in the brief moments when the groove passes up and down over the hole, rather than getting a good drink of oil by resting over the hole. A few seconds of this may starve the HLA to the point where it no longer closes the gap between the top of the HLA and the cam and you get the thrashing noises and loss of power.

These pictures come from two old BP heads of mine. On the left is a standard oiling hole. On the right is one which has been enlarged and extended upwards to correct oiling problems above 6000rpm. Sorry about picture quality, I capsized in the Buckenbowra River yesterday with a phone in my pocket.

[StanTheMan]

Thanks Phil. you're a wealth of knowledge.

base circle is 33.02mm

on another note:
If Ive gone too aggressive on the CR I'll try to reduce the lift a bit see if that makes a difference.
Just so I don't forget
Retard intake
advance Exhaust



probably run like a dog but we'll see what happens.

[manga_blue]

Thanks Phil. you're a wealth of knowledge.

Not that it's helped you that much. TBH I'd rather not be so well informed on problems with Bx heads. It took so much pain to get my car to reliably carry sustained use over 7000rpm. In hindsight 90% of the problems were related somehow to HLAs. They should never have put the bloody things on a sports motor.

[StanTheMan]

far out. I can thank my lucky stars.

At lunch I changed the setting on the cams Retarded the intake to increase the clerance on the valves advanved the exaust to clear the valves on that.

She runs sweet. Ptroblem sorted.

It must have been touching the valves.....ever so gently. We'll definately see on the way home tonight


Crikey's.

talk about Faulty Tower Risk management.

Your all aloowed to laugh, swear & whatever you feel is required. I seriously deserve whatever is coming my way. I should get the tool award.

anyway this isn't ideal I'll need to get a new head gasket. a thicker one. unfortunately this will reduce the CR.

[93_Clubman]

Crikey indeed! Thought you were at the limit in terms of a head shave, but wasn't sure how much if any more could be allowed for a thinner head gasket. Important thing is you've identified the issue quickly.

[bruce]

I am too afraid to laugh.
All strength to you, as I'm not as brave as you to do such things.

[greenMachine]

Stan, time to bite the bullet.

Pull the head, change the valves.

There are some good pictures on here of a piston and head where the valve head came off the stem, and it has happened to me too. It gets very expensive, very quickly.

Not what you want to hear I know, but if you have diagnosed the noise correctly you really have little choice - it is just a matter of when, and in what circumstances, and how big the bill is