Race Engine Forum UK

Hi Guy,

I am still working on the same engine that had the scored main bearings 3-4 months ago.
Well, actually it is not the same, as we ended up using a different block, crankshaft, and oil pump
for this buildup.
However, the results were the same: after break-in, about a dozen dyno runs and 3000 miles of
driving both the main and rod bearings are scored.
The engine is still running rich under certain conditions, but it runs in closed loop in normal
driving, so the ECU adjusts for close to stoichiometric (sp?) mixture. It was rich under full
throttle, where is would belch black smoke at a certain rpm. I now have it adjusted where
the AFR is 13:1 at full throttle throughout the rpm range, however there is still some black
smoke at WOT, which puzzles me.
It's hard to believe that over richness in some conditions would dilute the oil enough to cause
bearing scoring. Both the crank and rod bearings are standard size, and I checked clearance
with plastigage for each bearing.
I am running out of ideas on what to do. We will change to smaller injectors, which are
supposed to be easier to tune, but we were able to make the engine run lean with the
present ones, so I am not convinced that it will give us the needed solution.
Any ideas would be appreciated.
Thanks,

Csaba

Is the cause debris in the oilways? Have you unplugged the crank and cleaned it out? Have you unplugged the crankcase too?

This is a long shot, but 'magnetic' crank or rods (or even main bearing caps) can do this. If you use Magnaflux crack testing you have to demagnetise ('demag') the parts afterwards, otherwise they will attract ferrous debris.

Scoring is caused by debris (dirty build), poor execution of oilway mods, damaged journals, overfuelling and the above, and it can be caused by oil starvation too, for example where the sump has been 'bashed' and the oil pump pickup is being starved.

'Off the top of my head' I can't think of many other plausible causes.

G

Guy,

I have not unplugged the crank, just spayed carburetor cleaner through the passages. The last time I cut threads in the crank I broke 3 taps! And after all that I found the passages clean. I believe you use 3 different taps, a starter, a medium and a finisher? For the home mechanic this may be something better left to a machine shop.
Also have not unplugged the crankcase, just blew it out with compressed air. I need to find the appropriate size plugs. Years ago I had to cut threads in several customer's blocks for threaded inserts, as they had incorrectly inserted the oilway plugs, they blew out, and the proper sized one was not readily available.

Of course we had changed oil about a dozen times now, one would think that any debris would have come out...

I will check the crank and rods for magnetism, I assume they would attract ferrous objects?

Buying your DVD is on my to-do list :-)
Thanks,

Csaba

I have all the plugs direct from stock, the removal and fit/sealing procedure is documented with photos in my new book.

Don't try and tap the crank too deep - that's how you snap the tools. There is a step some distance down the oil gallery in the 4 webs and when the tap reaches it you stop! The no.1 tap does little more than generate a bit of thread for the no.2 to 'bite'. The no.2 needs to go much deeper. The parallel (no.3) generates the full-form thread. Again, this is explained in the above reference! The crank plugs need to be SHORT! I have them specially made for me.

Magnetic parts are the perfect trap for particles and I have seen this cause bearing failure.

GC

Guy,

I have ordered the block plugs here in the US, sorry, but shipping form the UK would be more than they are worth :-)

What do you think about refitting new standard cup style plugs into the crank? Is there too great a chance that they will fall out?

What brand are the taps you use? I have never seen such a 'three piece' set available locally. I assume they are available from an industrial supply company.
Thanks,

Csaba

Not entirely true "but shipping form the UK would be more than they are worth"

I figure it would cost £5 to mail a set.

No there is absolutely insufficient material to fit any other plug without extensive machining.

The taps are DORMER. 7/16 - 14 UNC. Can't get a set of 3? I can't believe you are so under-resourced for stuff like that in a manufacturing nation like the USA.

If you so thread out - you will definitely need the grub screws from me - unless you can buy very short grub screws Stateside.

I have never experimented with other thread sizes, the crank bore diameter is a bit of an 'oddball' size but perfect for 7/16 UNC.

I have just briefed Jon Logan in detail on this FWIW if you guys want to talk tooling..

G

Don't forget I run a tool and die shop among other things so these things are in stock continuously in my shop.

These tools and parts are absolutely available here. Hand tap styles sold commomly in the 3 piece set, 1 each of the 3 basic tap styles Taper, Plug and Bottoming finishing with the bottoming tap and after you create the proper tap drill hole size the taping is a snap.

Buy HSS (high speed steel) ground thread taps not the rolled thread/broached junk sold at a home improvement center or hardware store. The junk is typically marketed under Ridged or Vermont ETC so stay away from them unless you are taping wood (joke).

McMaster Carr will have all you need. If you need the plug part number I would be happy to post the number but since Guy sells them I will wait for an OK

Tap set $29.00 # 2521A774

Including the images for referance tap set ( note the leading threads are tapered differently) and plugs I used these can be shortened with a grinder if required but I did not need to.

Nice one, Robert!

I should be very happy to buy those plugs from you. Could you drop me a line at guy.croft@btconnect.com please? I'm having to have mine made for me which is a 'bugbear' to be honest and costly too.

Let me know price on 100 off?

Thanks,

G

Email sent!

Robert

CSABA!

FOLLOW UP!!

GC

Hi Guys,

Sorry for 'disappearing', sometime life gets in the way...

I still have not gotten the engine running, as we decided to go to a different, custom fabricated intake manifold,
and the manifold had to be re-made 2 times before they got it right. To their credit they fixed it both times for
free, but it took 2-3 weeks each time.

I took out the oil galley plugs from the block and cleaned it out with a gun cleaning brush. The galley appeared
to be clean. I took the crank to the machine shop and had them remove the factory plugs, clean the passages, and
insert threaded plugs.

The engine is assembled and installed into the car, I need to bolt on the ancillaries and get it running, however
I have the holiday family happenings starting this weekend, so it will be January before it is all finished.

I will let you guys know once it's running!
Thanks,

Csaba

Hi Csaba!

Did Ramzi get to you??!!

G

Hi Guy,

Yes, he let me know I have some unfinished posts here :-)

bye,

Csaba