BMW K1200RS - Possible supercharger conversion
Turbo Mini Forums

good point about taking a little off the valve stem. much cheaper solution that new buckets at 20quid each!!

Anyone able to confirm that valve clearances should be:

• Intake: 0.15 mm to 0.20 mm (0.006" to 0.008")
• Exhaust: 0.25 mm to 0.30 mm (0.010" to 0.012")

Sorry you had you had to go to the effort of finding out for yourself what several of us had told you, but hopefully now you understand why the leakdown tester up-front, would have saved the effort of disassembling the engine.

For the head itsef, just take it to a fgood machine shop outright. Tell them to re-cut each and every valve for good measure, and that you suspect one of the valves on #2 has a problem.

Tell them to also machine the stems down to retain the original height to avoid having to buy new buckets.

Ha . dont feel sorry for me. The engine was in bits and out the car before i'd even heard of a leak down tester! It was worthwhile having the pistons and bores inspected for belt and braces piece of mind before i was to trust that it was valve issues only.

The head is getting inlet seats and valves cut as i type this, so failing any hold ups, should be getting built back up in the next week or so. They vacuum tested the head and exhaust valves were perfect. Inlet valves were only just in the green on the gauge and nowhere near the exhaust readings. The suspect valve gave the poorest reading and miles from green, so more confirmation there.

They are going to machine the stems down and i've given them the above clearances so hopefully they are correct!!

Cheers,
Nick

I'd build it up with a little plasticine on the piston cut outs to verify you have enough radial clearance. Something made them bend. Maybe it was the donor engine? Maybe it's yours. I'd check it for sure.

The valves havent bent, i believe its been excess heat that has caused the seal between valve and seat to become ineffective. I also think that when its been dry decked, the heat from the welding has maybe caused one of the valve seats to shift alignment slightly.

Now ive got a much bigger radiator, much higher volume of water flow in the head via the dry deck and fully sealing valves.

NOt much more i can do, so we'll see if it delivers and takes some punishment on track in the next few weeks!

Any Updates?

Worn thurst faces on the crank put a stop to any fun earlier on in the year. Getting married and fitting the big end bearing caps the wrong way round also scuppered plans for end of season entries!!

Engine is finally going back in the car this weekend but I won't really know if I've solved the overheating and head gasket munching until I've given it some abuse on track. Might try and arrange some track time next month and if it survives then ill be happy to fettle with it over the winter months ready for spring.

Time will tell if thats the end of the issues then.

What head gasket did you resort to in the end? Been toying with going 73.5cc with one of these to reduce lag on the new engine.

http://minispares.com/product/Classic/Engi...k%20to%20search

Any updates?
Cheers,
Mark.

Edited by nky_84 on 27th Feb, 2016.

Oh bollocks.

In the 13's at last!.. Just

That doesn't look good

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Bloody hell, your not having much luck at the moment with this. Hope you get it back together soon. Best strip and clean everything.

You will have to do some measuring but it might clean up with a hone through the mains and a grind on the crank.

Looks like the thrust face might be dead too tho for that kind of damage on the cap?

That will need a line bore for sure!

Looking at number 1 bearing, the way it has failed, is because the crank has in effect sealed off that side of the bearing. This prevent oil flow out that side, and is likely why that side of the bearing has failed.

RTS..........

Just a hone through the mains would be ideal. The crank looks much than it is and might just get away with a polish but will let machine shop decide.

Thurst faces are all perfect but the cap is scrap. Not sure how easy this will be to source

@sprocket - any ideas why it's failed in this way?

The car does so few miles. That changing the thrusts once a season and keep ing on top of any symptoms doesn't warrant an rts build in my mind. Are they not limited to below a certain power and torque that this setup is capable of producing?

Firstly, what clutch are you using? And what do the thrusts look like? What was the installed end float?

As for bearing housing in the block..... I had to have mine line bored as the housing deformed with the heat. The new bearings would go in ok but measuring the roundness showed that it was so much oval that the crank journal wouldn't sit in tha bearing without pinching.

Thrust failure is the main reason this happens. When depressing the clutch the crank is pushed towards cylinder 1. If there is enough displacement in the thrusts, the crank web is allowed to run on the block and cap. As the crank has worn into the block and cap at number 1 bearing, its creating a restriction to oil flow leaving the bearing on that side. Since the oil is fed into the bearing from the top grooved half, more oil if not all of it, has to flow out the other side of the bearing. Since there is little or no oil flow in part of the bearing, it will tend to run hotter in that area, compounded by the heat generated by the crank munching the block and cap. The result is that the bearing grows, grabs the crank and spins in the housing.

This looks like a thrust issue, that some on here have experienced as a result of the preverto clutch and grey or double grey diaphragms, especially whin the diaphragm hasn't ben correctly set.

While the RTS isn't the lightest clutch in the world, it somewhat gets round the thrust issue. You might be able to get away with just using the uprated diaphragm rather than building an RTS depending on peak torque. That said you shouldn't really have a problem with a well set up preverto clutch on a normally aspirated engine.

Edited by Sprocket on 28th Feb, 2016.

if the caps scrap you'll almost certainly need to line bore it with the new one.

what were the bearing clearances like?

Thanks. Very helpful! !
Thrusts are brand new and look brand new. As I say. Clutch has only been depressed about 20times since new crank and thrusts installed. The old ones were in bits though!

Clutch is a grey preverto paddle setup. Also had a knackered clutch arm which wasn't helping which has now been replaced with the uprated version.
End float was 0.004 I think.

I've had big time thrust issues before but I think I've replaced everything apart from the bearing cap which I think has caused this issue. Now Im aware of it I don't think it's an issue for me as the setup should last a few 100 miles and that's all I need. Rts sounds great for a road car but if this all works then I need something that can cope with 250bhp and associated torque that is light and simple

for my money I would always go RTS, unless building a screamer track car, ultra light verto back plate will get you a setup roughly equal to a lightweight road preverto,

I'm wondering if the bearing cap was sitting pissed so one thrust was taking all the load.

If you are going to get it line bored, you may aswell get a cast 4 bolt centre main cap and and that fitted at the same time.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

^^ good point,

dont go for a cheap cap though as they dont bore that well,

Also swiftune cap dowels... well worth the money IMO

If there's nothing wrong with the thrusts I cannot see how the crank has worn into number one bearing housing like it has with only 0.004" clearance.

In that case, the bearing housing is deformed