BMW K1200RS - Possible supercharger conversion
Turbo Mini Forums

the last gasket fitted pictured way up (BK450), I can see a tell tail mark on the gasket at the rear of the cylinder. Whether this is down to blow by I do not know, but I can see a difference in that section alone.

Drop the head onto the block with studs fitted without the gasket, and shine a light while looking at where the two meet to see how well the head sits on the block to begin with.

In my experience, drilling the studs direct into the block after plugging causes enough skew on the studs to make the head tight on the studs. It usually gets tighter as the head gets closer to the block.

I have also experienced replacement studs stretch significantly, in fact under normal torque settings I managed to put one into its plastic region. They all went in the bin! Now Those studs you are using, judging by their finish are either standard replacements (if they are, bin them now), Minispares uprated (not much better in my opinion) or ARP (probably the best option). I sought out Genuine OEM studs from a few scrap 998's (next best thing to the ARP's in my opinion)

The BMW torqueing sequence is freely available in the BMW workshop manuals, seek and ye shall find

also, it might just be the picture, but is there evidence that the inlet valves have been catching the pistons on the very edge of the valve cuts? difficult to see in the pictures but there is a glimmer of silver with what looks like a shallow ridge. could just be a shadow and reflection though

Hi guys,

Well ive been having another look at this and the only conclusion i can come up with is the overlap of the gasket is causing the issue. I'm not sure why its out of alignment or how but i think this may have been my problem all along. The original bimetallic gasket was a better fit, higher grade and the NA didnt push it hard enough to fail.

The conversion to turbo has upped the pressures and temperatures and the misalignment eventually gave up after the rolling road session and 5mins of track abuse.

Two solutions that may or may not work...

1. i elongate the stud holes in the gasket so that the gasket has a chance to line up with the bores, but ive got concerns about how i keep this central until the head is bolted down.

2. spend £200 on the "very high performance" gasket http://twinkam.co.uk/epages/191f6b26-60bf-.../Products/SC273 that has monster fire rings that will go a long way to stop any gas leakage, even if there is some misalignment but its £200 down the drain if this isnt my issue and it fails again.

Overlap:



Test drilling previous gasket:


Anyone have any ideas why it would be so out of alignment? Bores or studs out of alignment? Do the water holes etc usually line up perfectly with head and gasket, this seems miles away.

cheers,
Nick

Edited by nky_84 on 2nd Apr, 2015.

It's overbored right? It's probably just been done badly and not offset correctly

Number 1 imo.
Tack it to the block with superglue to keep it where it should be till torqued up

Yes. 1380. Specialist components did it or at least sourced the block and did the machine work so would of thought it would have been done correctly.

For the sake of a tenner I'd be temped to tweek the gasket holes and do as Joe's suggested.

Small update. I realigned the gasket and still got low compression. moved onto valves and discovered that one of the inlet valves was leaking air into the plenum. Head off again and lapped it in with grinding paste. Seemed to do the trick and is now not leaking. Compression test again and still 50psi..

Carried out a wet test by dropping some oil in the cylinder and I got good compression albeit briefly. So looks like I'll be stripping the engine down again to inspect bores, rings and pistons a little closer than last time...

If you have a valve leaking enough air to notice it ain't because it needed lapping, it's because it's bent or it ain't machined right. If it worked once, then it's bent...

You can check yourself by putting engineers blue on the seat and the valve, then some super-fine lapping paste. If all the blue is wiped off the seat but a small amount left on the valve, it will tell you the way forwards...



As regards the gaskets - what Joe said - or use some masking tape in each corner, then lift the corners (one at a time) and peel away the tape.

Hmm, knowing my luck with this build you are probably right. I pencil marked the seat before and after the lapping and the difference in the markings was pretty clear and it does seem to have made a big difference to the sealing. I'll revisit again after the block investigation

First off, you need to put the compression tester away and buy a leakdown tester. The beauty of these, is that they let you "hear" where the issue is....


Here is a crazy idea...

The head in these has equal spacing, and the stud holes are symetrical about the chamber...
This means any chamber in the head can locate over any bore by just using the four studs. If you have low compression in #2 but are good on the others, simply spin the head around 180 deg and re-clamp it down, or move it along one bore.
This way, if the "issue" stays with cylinder #2 you know it is the piston/ring, but if it now is a different cylinder, you know it's the head, and you know it is almost guaranteed to be one of the four valves...

if you spin the head around, how you going to turn the cams? ok with a leak down tester though

Team www.sheepspeed.com Racing

An old Vauxhall BTCC trick, turn the head 180 degrees and have the inlet at the front and exhaust at the rear :)

I had that crazy idea too.. when I flipped 180 I got some odd and very low results across all cylinders so I had assumed that things weren't quite symetrical. Didn't fancy shifting one bore over and leaving one end unsupported

You have some weird stuff going on then...

Just to be sure: With the leakdown test, you need to rotate both cams so the valves are totally closed for each cylinder.

There is no reason a 180 spun head should not work for a leakdown...

Today's 'progress'

Attachments:

1.58mb

Pistons removed and bores inspected. Nothing obvious so think I'll have to take it to a machine shop for advice/proper inspection.

Well I'd have put money on a set of ring lands missing with those compression figures. Hope you get it sorted soon.

get the lands checked for any tapering,

Guess it will be worth checking piston/cylinders are still round too.

Out of interest what did the revs peak at on your rolling road video? looks like it lost traction.

which video are you referring to? Think it went to about 7.5k on a power run. On the runs it lost traction, it hit the limiter which i cant remember what its set to, less than 8k though.

I still think its the valves. If a valve was definitely leaking air into the plenum, then it means a valve is likely bent.

Leakdown testers are about 40 quid, and would have pointed directly to the problem. I always reach for the compression tester first to identify problems, but once the problem cylinder is identified, the leakdown tester is used to identify the problem inside the cylinder. Bubbling coolant, air out of adjacent plug holes or the gasket line = gasket. Air out of the crankcase = ring / bore issues; rotating the crank about the compression/ignition stroke allows you to see if the issue is isolated to any one part (which would suggest a bore issue). You can then further isolate the piston / bore issue by pouring a small amount of 20/50 into the bore; enough to cover the whole piston crown, which will all but isolate the air moving down between the piston/bore/ring.
If the bore/piston seems to check out ok, then you pull off the exhaust and inlet, and listen for air...

Yes, this one tool (and a compressor to drive it) can pretty much tell you the problem without even lifting the head.
Trying to identify bent valves, or damaged pistons / rings (in comparison, by full dissasembly) is a pain...

Edited by TurboDave16V on 27th Apr, 2015.

May well still be an issue with the valves but i the wet test results and crank case pressure were a pretty sure sign there is piston/ring/bore issues so needs a strip down anyway.

I dont own or have access to a compressor but i might look into one and a leak down tester i / when my troubles continue as it does sound like a required bit of kit!

Thanks for all your help and advice. Will update when i get booked into the machine shop and see what they have to say.

Took pistons to a machine shop and they couldnt find any wrong. I have now purchased a leak down tester and sourced a compressor.

All of the cylinders caused the gauge to go off the scale in terms of 0 leakage once i let more than 20psi into them. I could hear air escaping into the bores but i've read that this is to be expected.

When i came to cylinder 2 inlet valves the one that i thought i fixed is still leaking badly (even though it registered nothing on the leak down gauge) so it seems to still be a problem here.

I have previously swapped the inlet valves round and the issue remained on the same inlet, so i dont think its a bent valve but will get this checked. It appears to be an issue with the valve seat, which im going to take to machine shop for inspection. 2 other inlet valves were leaking very slightly when i cranked up the pressure so the whole inlet side may need some work.

Not got any experience of this process. Is it expensive? Anything particular to watch for in these heads? Do i then need to get new buckets to suit?

If you do need to drop the valves in the head a bit you could always machine a touch of the top of the valve stem, to suit the new clearance.