Great tech thread on these engines. I am really enjoying this. I, as an old guy am way impressed with that .00175 clearance number. I had no idea you could do that. You would not believe the slop we used back in my youth ( 1960's ) on American engine builds. We thought we knew what we were doing.

 

Avoid Rennwerke Porsche in Elmsford, NY like the plague... and avoid buying any car that this shop worked on!

Cheech (the owner) will promise your car in a week, and deliver it YEARS later, and as a ticking time bomb that you will not be able to even make it home in without a tow truck... plus, with a bunch of scratches, parts stolen off your car, and probably parking tickets from him using your license plates to drive other cars around!

(I'm not even close to exaggerating or joking, he actually has had the ***** to do all of this).

And if anybody reading this does go to Rennwerke and thinks that he is doing their cars justice, trust me, unless you are famous (like Jerry Seinfeld or a basketball player), he is sabotaging your car, putting in used parts from his old cars and stealing your new parts to put in his cars.

 

Being unfamiliar with this forum - I am getting confused as to who some of the responses are directed towards?

I was just originally responding to the title "bore score which way to go" providing our experiences from the UK.

I hope for example that German 888 didn't include me in his "run a mile fast" list as my last post couldn't have made it more clear that different solutions can be equally or similarly effective.

Jake - we have never used any target times nor do we record production times on ANY WORK (so our work ethics seem to be the same) and I agree it is only the quality of the job that is important and they are all different. Target times lead to bad decisions and workmanship - but we do have a generous profit share scheme to encourage employees and longer holiday entitlement for long service - with many employees now with an extra weeks holiday/year having worked for us for over 15 years. Our management style encourages a management structure that seamlessly flows up and down with regular meetings and ideas.

We don't rush jobs (appreciate the implication from our time lapse video) but 1/day does not mean in and out in a day - just one finished and one starting every day. Usually around 3 to 4 weeks is the total build time with the decisions from the owner about the final build spec the greatest delay. This requires considerable storage and planning to accommodate so many crankcases, engines and cars at various stages of build.

Some are mentioning $20K typical costs. We have different rebuild options that range from car in to car out to just fitting cylinders to crankcases - but for a full job our usual costs range from around £8K to £12K (the former being with re-usable crankshaft, 6 alloy Nikasil cylinders, new bearings, recoated pistons, new rings etc) - the latter being with all new pistons, latest IMS shaft (or our modified earlier version fitted with the larger bearing) and usually a new flywheel, clutch, coolant pump or other work included. I guess this makes our price range $10K to $15K for a full rebuild although it can often be less.

We are not however pushing for US business - as I made clear in my last post we are busy enough and neither need or want any more work in the UK and our only expansion could be the provision of our range of parts under licence (which is currently being developed in Canada) although that has not been the purpose of my posts which I repeat are just to add information to the original question.

To answer another question - we use aerospace billet alloy and the expansion coefficient is a negligible difference to the crankcase cast material. You have to be careful working out expansion rates because piston crowns run hotter than the coolant and so does the alloy or steel in the cylinder - and further more dissimilar materials in the thermal flow increase the delta temperature as well. By all usual calculations steel needs around 1 thou (0.025mm) more cold clearance than aluminium.

Piston design is a complex subject. There is basic design, ovality, barrelling and taper to consider. There is also the basic and running clearance because the tighter the clearance the more ovality is need etc. There is an old saying among reconditioning shops that "if it's slack it won't come back but if it's tight - it might". We do not follow this and presently our test engines are running with different piston shape designs (none failing) but all to assess the wear rates, pressure points and support areas (in conjunction with a prominent F1 supplier with World titles under their belt).

While analysing all the alternative pistons available for these engines - we found most suppliers that traditionally supply the racing market using more ovality and taper than manufacturers of "road use based pistons" - and this will make them less likely to seize but more noisy. It may also increase start-up smoking in this engine layout when the horizontal cylinder layout prevents oil from draining away at rest and ring gap positions and cooling rates can allow a film to be washed by the next "rich" start-up.

I am sorry guys if by just informing the World market of our recent time laps video - and becoming involved in adding specific technical information to answer this original post - I seem to have invoked a defensive and competitive reaction.

I do notice however that it still appears that no one else machines the top of the M96/7 block (so it fits like ours to support the cylinder) like the GT3 and Turbo pictured block in the earlier Flat 6 pictures do. Having a top hat sitting in space does not make it a closed deck.

In my view there is going to be enough work fixing these engines for all of us wherever we are and there is never any harm in allowing the readership full knowledge of ALL ALTERNATIVE OPINIONS AND SOLUTIONS WHEN TRYING TO DECIDE WHAT TO DO AND WHERE TO GO!

Baz Hartech www.hartech.org

 

Baz,
Your final paragraph below illustrates the only issue I was trying shed light on. As someone who's facing this daunting decision with very little knowledge It's a challenge deciding which method to go with. In my personal discussions with 3 different builders each has had a very different process. Add yours and Flat 6 and the choices are becoming a bit overwhelming.

Thank you again for the informative response.

 

Very interesting and informative. Thanks for taking the time...

 

Instead of starting a new thread I will continue here:

- 2006 C4S with 106k miles / original owner / meticulous maintenance routines
- Car started to use about a quart of oil every 200 miles or so lately / knocking / smoke left side

Scope ravelled scoring 5 and 6 cylinder.

Currently looking for a rebuild, as much as I would like to go the LN 4.0 build... I don't think I can wait for a year to get the car back.

I'm now considering either a block from RND or a 4.2 build from Dwain at Vision. Any feedback would be appreciated!

 

I've talked to Dwain a few time and he seems like stand up guy. He also has a great reputation. Do you track the car? If not, RND would be a cheaper option that would be fine. If you do track or think you might, go with Flat 6 or Vision. There's a few others around but those seem to be the two I've heard the most about.

 

Turn around for Nickies is 6-8 weeks. I know we get backed up, but a year is a bit much :-)

RND Engines give you the Nickies, but stock displacement. Flip side is near instant gratification.

Vision used to do Nickies - they do steel sleeves now instead. Cheaper and quicker to install.

 

Im very sorry to hear that. That really sucks. C4S...is it a cold weather car? At what miles did you begin to notice? What oil did you use?

On the plus side sounds like you've got a killer rebuild in your future that will give you another 100k+ miles.

Keep us posted on your plan.

 

When I went down the list of stuff RND does in their process, my local shop kept telling me item after item was unncessary overkill--but they were going to charge me the same as RND. Needless to say I went with RND. One word of caution though, be really careful about the shop you use to do the swap, and stay on top of them and make certain they follow RND's directives to the letter as to what ancillary items to check/replace, and how to do the break-in.

 

Yes, cold weather driven in Canada. Motul 5w40.
Im really hoping to get another 200k miles from the rebuild to make it worthwhile!

 

Based on the posts ive seen C4S's seem to be the biggest victims of bore scoring, for the simple fact they typically live in colder places. Not sure why the Germans didn't pick up on this earlier.

Any other details you can share would be useful for posterity:

- Was the car stored outside?
- Was it used year round or stored during the winters?
- Was it a DD with shorter hop drives?
- What type of oil change schedule?
- Tracked?
- When were symptoms first spotted?
- What were the first symptoms: did oil use start to increase, sooty left tail pipe, etc?

Im excited to see the future threads on the rebuild and getting back on the road.

 

[QUOTE=TheBruce;14831856]Based on the posts ive seen C4S's seem to be the biggest victims of bore scoring, for the simple fact they typically live in colder places. Not sure why the Germans didn't pick up on this earlier.

Any other details you can share would be useful for posterity:

- Was the car stored outside?
The car was always garaged inside except for the last 3 months.
- Was it used year round or stored during the winters?
Year round use from day one. 106K MILES
- Was it a DD with shorter hop drives?
It's my second car but I use it on short drives A LOT
- What type of oil change schedule?
3000 miles or 6 months. MOTUL 5W40 / LN SPIN ON ADAPTER / MAGNETIC PLUG
- Tracked?
Never
- When were symptoms first spotted?
A month ago
- What were the first symptoms: did oil use start to increase, sooty left tail pipe, etc?
Smoking at start up and 5 litre of oil consumption in less than 1000km. Sooty tail pipes were always present (running x-pipe cats)

This car was over maintained; I have receipts to fill a library

 

Wow! Thats scary. Hartech's guide said it can progress quickly, but that is really fast!!

Anything you can think of that could have contributed?

 

Holy Oil Consumption!