Race Engine Forum UK

Hi, I'm new to this forum, but not to Fiats & Lancias. My first I-car was a Fiat 124 Sport Coupe, then a couple of Fiat 850 Spiders, and in 1981 I bought a Lancia Scorpion that I still own. This car has slowly progressed from dead stock to a street car that is also fairly competent on the track. The car currently has a 16V Thema turbo engine with a lot of upgrades, and that is the subject of this post. I recently experienced my second rod #1 big end bearing failure, so that has prompted me to investigate what the cause might be. In each case, there was an overall lubrication problem, however the #1 big end and/or main bearing failed quickly and dramatically whereas the other bearings showed minimal wear.

I removed the oil galley plugs and saw immediately that the oil feed bore for main bearing #1 (which also feeds rod big end #1 via the crank) appears to be improperly drilled. It looks as though the drill drifted off course, and ended up breaking through into the adjacent cross feed bore that goes across the front of the block. This cross feed bore connects the oil input into the engine from the oil filter manifold across to the other side of the engine and into the main oil galley. Because the #1 bearing bore and cross feed bore are nearly parallel, the two now intersect at an acute angle and there is a razor edge where they come together and about 1/2" of length where the two bores are open to each other. My guess is that this creates a big problem with #1 oil feed, because the #1 oil flow direction is opposite the cross feed oil flow. I would expect a big pressure drop in the #1 feed as a result. To make matters worse, the intake cam oil supply is ported into that same #1 bearing feed bore, increasing the required flow through that bore.

I've tried to take a few snapshots to show the problem. These photos show the front intake side (remember this is a reversed flow version) of the engine, right side up, where the cross feed bore was drilled (later capped by a plug, which I've removed). On the left you can see the start of the main oil galley. You can see the #1 bore breaking through into the cross feed bore, and a dark circle at the top of the #1 bore which is the intake cam feed bore. The pictures are taken under different lighting conditions, including shining a flashlight down some of the bores.

I have a few questions:
1. I assume of course that this is a defect, and that normally the #1 feed bore would connect directly and only to the main oil galley at 90 degrees. That's what I'd expect, and that's what the factory manual shows (see picture). True? There are virtually none of these engines in the US so I have nothing to compare to.

2. Do others agree that this would cause a pressure drop and reduced flow through the #1 bore? A minor problem or serious?

3. Assuming it IS a problem, what can I do? My best solution to date is to remove the sharp edges with a dremel tool, drill & tap the port shown in the pictures, and use an external oil hose to feed oil from the intake side. This way, the flow in both intersecting bores is going in the same direction, which should eliminate a pressure drop in the #1 feed.

4. A related question - the factory manual (attached) shows 3 oil feeds for each cam, front/middle/rear. But, both my block and head are set up for oil feed only from a single feed per cam, at the front of the engine. Is this normal? I love my new C&B cams that I purchased from GC and would hate to see them damaged!

Sorry for the long-winded post. I welcome feedback from Guy or anyone else with insight on this problem.

Thanks,
Ken H

Hi Ken

sorry but I have had to take down the OE manual cutaway as publishing infringes copyright. Pity but there we are. No point upsetting Fiat.

Nonetheless you wrote a very good, detailed post on a thing which is not easy to describe. I have pulled out a block and compared against your notes and I can see exactly what you're referring to now.

Speaking as one who potentially might have to deal with something like that I would tackle it as follows:

1. The main journal housing oil feed (oblique drilling) misalignment into the longitudinal gallery and interference with the main input drilling will not per-se affect the delivery to crank. I judge that it would not affect delivery any more than if the drilling were in the right place, ie: separate and only into the longitudinal gallery.
2. The excess metal sticking out into the longitudinal gallery is definitely a bad thing and should be fettled out as you indicated. There may have been other associated loose metal bits breaking and coming off that region too which would go straight into the bearing. Whether it would interfere with delivery to no.1 crank journal I'm not so sure, my feeling is that it would give feed priority to no.1 and tend to starve the others. I would definitely not undertake any special oil feed piping/drilling work.
3. If I'm wrong about interference (as in 2 above) then it might be the cause of the bearing failure. If I'm right there must be another cause, so (and in any event ) check out these other issues too:

a) Strip and inspect the oil pump and strainer and rebuild thoroughly.
b) Strip completely (not easy) and clean the thermostatic oil filter housing
c) Junk the oil filter and pressure clean all the oil galleries, hoses and oil cooler
d) Clean out the sump (sorry, a bit obvious)
e) Unplug the crank oil drillings (4 off) and tap out at 7/16 UNC, I can supply plugs for this, there may be debris in there from bearing failure and this will carry over from one build to the next.
f) Check the crankpins and rod big-ends for size. I have the data if you need it, feel free to report back and I will tell you if the sizes are acceptable.

As far as other cause of failure is concerned it could also be attributable to:

i) Low grade oil or loss of viscosity due to over-fuelling (see ancillaries in GC V/W).
ii) Oil starvation in the sump - the most common cause of bearing damage on a powerful motor - go to decent baffling or oil pressure accumulator is recommended. From memory the sump on that motor is nothing special in terms of oil control.
iii) Overheating oil - I recommend an oil with 60 high temp viscosity rating, fully synthetic, maybe Millers or Redline if you can't get my favourite, Selenia Racing, and the oil temp must be sustained under 95degC at all load conditions. If the oil is too hot the bleed-down rate is simply too high for the pump to keep up and metal-metal contact will follow swiftly.

There are only 2 oil feeds from the block to the head on your motor, these 2 vertical drillings at the front L & R of the block feed the pipes on the cam journal housings. Nothing wrong with your engine there! The factory dwg is wrong, or maybe some early projected setup that I have never seen.

I hope this is helpful at this time.


GC

Hi Guy,

Thanks for your detailed feedback and suggestions. Apologies for posting from the manual - as you say, we don't want to upset Fiat. Based on your comments, let me provide a bit more information on my situation:
1. Interesting - I had thought the geometry resulting from the break-out would affect the flow. Of course if the oil velocity is low, it won't make a bit of difference. Has anyone measured actual oil volume flow on a TC engine? I've bench tested the pump's static flow but of course much of this is diverted by the pressure regulator valve.
2. It's hard to tell from the pictures, but there is little or no projection of metal into any of the bores, so no worries there. I'll do some clean-up work on the sharp edges.
3. a) Yes, I will go over the pump and strainer in detail. Since the strainer is a sealed item, not much I can do other than a visual check and a solvent flush.
b,c,d) Yes
e,f) In my case, it's not a crank problem, as I'll explain. I had cleaned and plugged the original crank as you suggest when I first built the engine. After the first episode (a dry sump pump failure, which affected both #1 main and #1 rod journals, but nothing else), I elected to purchase a new crank from Fiat. The second episode was with only 2K miles on a brand new crank and bearings. I checked clearance during build and found it within spec; however (and I'm kicking myself now) I did not check ALL the bearings, so it's possible #1 rod clearance was incorrect.

so that leaves us with:

i) I was running 10W-40 Castrol on its second oil/filter change since the rebuild, and about to switch to synthetic @ 2K miles. Over-fueling could be a possibility, although I don't smell any gas in the oil and it looks normal (except for the bits of bearing!).
ii) After giving up on dry sump after the pump failed, I modified my Thema pan to match the Montecarlo design, with similar baffling and trap doors and a windage tray (as permitted by clearance for the oil pickup). A 2 qt Accusump is installed and operational. The oil pressure has always been solid on this engine, 40-60 psi at cruise. I have a good quality DEFI gauge and a working oil pressure light that has never come on with the engine running.
iii) I'm running closer to 100-110C normal oil temperature, so maybe I need to relocate or improve my oil cooler.

The first bearing failure was on the track after my dry sump failed, so certainly a spun bearing wasn't a complete surprise. However, the second failure occured on a new-ish engine build while driving down the highway at 3000 rpm. That one is hard for me to explain, as the oil pressure was fine and the oil light was off. There is a major problem somewhere, and I'm still on the trail. I'll do some more checking based on your advice.

Thanks,
Ken H.

It's hard to tell from the pictures, but there is little or no projection of metal into any of the bores, so no worries there. I'll do some clean-up work on the sharp edges.

Sorry, Ken, yes, my error, just a trick of the light, looked like a piece of metal sticking into the gallery, and yes, I can focus on it as it truly is now.


You need to plumb the feed line to the accumulator into the filtered engine-feed gallery (maybe via a redundant oil pressure/temp sender port, using an in-line one instead) in the oil filter housing if using the OE item, are you sure you have it plumber in right. Get it wrong with a thermostatic unit and it might not be working. You would also probably need to use a non-return valve in that feed line. You're the expert on your own engine, you tell me it's OK and I'll believe you!

I don't consider the drilling to be contributory cause. I cannot think of anything just at present that I can usefully add. Thanks for embracing the advice from me, clearly you have a very well-constituted setup there.

GC

Hi Ken

I looked inside two of those blocks this week and they both have identical drilling features to yours, so that's not a defect for sure, just inherent in the design.

GC

Guy Croft wrote:Hi Ken

I looked inside two of those blocks this week and they both have identical drilling features to yours, so that's not a defect for sure, just inherent in the design.

GC

Guy,

Many thanks for the follow-up! I've made a quick sketch below just to make sure we're on the same page. I hope it helps.

I was expecting the oil feed hole for #1 main to be parallel to the oil feed hole going across the end of the engine, but instead it intersects at a very sharp angle of just a few degrees. The jagged edge of metal that was left was not cleaned up in any way, and even if this did not create flow problems it certainly would create a danger of a small piece breaking off and ending up in in one of the bearings. Is this similar to what you saw? I've cleaned up the sharp edges and am jost now in the process of putting the engine back together.

Regards,
Ken

Hi Ken.
Iam trying to get as much information on the 16v engine as possible on why this engine is losing its bottom end. Iam now up to 22 engines ive seen with scrapped bottom ends and just about all of them had Number One rod bent, and the bearing completely "cooked". The inlet cam was also severely worn. What i think is happening, is a piece of metal is blocking the galley way as per your pics and drawing. This is effecting both N/A and turbo applications.

Andy.

I said earlier - The excess metal sticking out into the longitudinal gallery is definitely a bad thing and should be fettled out as you indicated. There may have been other associated loose metal bits breaking and coming off that region too which would go straight into the bearing.

Having seen two like Ken's and revisited this thread I'd now be tempted to relieve that oil gallery region on every one I do from now on. Whether it is contributory cause I doubt we'll ever know but better safe than sorry.

GC