Lotus Elan and Lotus Elan Plus 2 Forums

I have seen rods and cranks break and blocks split but never seen a main cap of any type fail personally. My comment above that I beleive the original round main caps can fail around 8000rpm came from a comment I thought I recalled in the Vizard book which I dont have with me currently so I may be wrong as to the source.
cheers
Rohan

I have been trying to keep out of this as I don't race and I don't build race engines. I have taken apart my share of Kent based engines and I have only seen ONE round main cap broken into two pieces. I don't remember if it was the front or the rear but it was one of the end caps. It may have been a 1500 I don't recall, they all look the same to me. I don't have a number but I'd guess the total number of Kent blocks dissassembled is on the order of 15 to 20, not a big number and I have more experience with Coventry Climax fire pumps, at least on the disassembly side of things with 30 or so kills. I have the Vizard book and have a couple photos of the chapter on "Prepairing and Strengthened Bottom End"

To me it reads do a tuftrided crank and rods with steel main caps. This combo is safe to 7500 with short bursts to 7800

Please read and draw your own conclusions





Steel or 711 square caps is just cheap insurance when you are building a 1600 twin cam that will be on the north side of 165 hp and have some real money tide up in it. If it was just a beater road rat then maybe I wouldn't spend the money. But once you get past iron 125E Ford crank you are starting to get into serious money and you need to protect your investment. That goes for the oil and cooling system too.

Gary

Thanks Gary

the Vizard info IMHO puts a historical perspective on the justification for the bearing replacement - - steel caps are used to keep bearing distortion & crank whipping in check so as to minimize vibrations - no doubt a real concern for a surfaced hardened iron crank in combination with preped 125E rods.

There is camp here that tries to avoid the 15 thou boring - I like the logic there and so am leaning towards the 711M caps in the hopes of being able to use just a hone vs an all out bore

We might be looking at a case where people have been doing this for so long they forgot the reason why.

George

A good shop can line bore a new set of caps without removing any signficant amount of material from the block. The caps are machined on the faces and then assembled to the block and the line bore done to the original O/D by removing material from the cap and to only just remove the absolute minimum of material from the block side to get a straight bore. You end up only taking a thou or so off the block side in most cases.

cheers
Rohan

If the round caps were ok for a high performance engine then why on earth would Ford take the engineering time design new caps, make new patterens, cast new caps with more cast iron and fit them across the whole range of engines both low deck 1300 and tall deck 1600 along with the Lotus used 1500 height blocks. Ford must have had some real concerns, otherwise they could have used the same round caps until the end of production.
I don't believe this is a wives tale or whatever you want to call it. Ford would not have spent the money if the round caps were good enough for the job, thats just the way it is. If they could save a penny on each cap you can bet that they would have.

Gary

Hi Gary,

why on earth would Ford take the engineering time design new caps, make new patterns, cast new caps with more cast iron

While no one disagrees that Ford did this for a reason, I for one am not sure why, but if we use Vizard and your insight into Ford culture, I would offer up some more conjecture on why this course of action was followed .

1.) Redesigning the caps is cheaper than fixing (upgrading) the crank. rods, block etc
2.) The problem that was there in the 72mm config was even worse in the 76/77mm stroke config ( this is still a problem with the FF guys even with the big caps ) see number 1
3.) The wall thinkness on the block meant that stoking was the avenue for displaceent, see no 1.

So if we follow the logic that ford were cheap $#@&!&^* then the cap fix makes more sense ( for them anyways)

Its kind of a moot point for me as I have caved to conventional thinking and will now be looking into getting the right machine shop to look at the option of installing either the 711M or Billet steel. They just have to be able to meet the spec . To your point cheap insurance. More controversy to follow - oiling, induction, exhaust are topics to be queued up in the future.

G

cabc26b wrote:Hi Gary,

why on earth would Ford take the engineering time design new caps, make new patterns, cast new caps with more cast iron

While no one disagrees that Ford did this for a reason, I for one am not sure why, but if we use Vizard and your insight into Ford culture, I would offer up some more conjecture on why this course of action was followed .

1.) Redesigning the caps is cheaper than fixing (upgrading) the crank. rods, block etc
2.) The problem that was there in the 72mm config was even worse in the 76/77mm stroke config ( this is still a problem with the FF guys even with the big caps ) see number 1
3.) The wall thinkness on the block meant that stoking was the avenue for displaceent, see no 1.

So if we follow the logic that ford were cheap $#@&!&^* then the cap fix makes more sense ( for them anyways)

Its kind of a moot point for me as I have caved to conventional thinking and will now be looking into getting the right machine shop to look at the option of installing either the 711M or Billet steel. They just have to be able to meet the spec . To your point cheap insurance. More controversy to follow - oiling, induction, exhaust are topics to be queued up in the future.

G

Hi George

Once the ball gets rolling its hard to stop.

The 1600 had new rods that are pretty good, they had a heavy piston with the combustion chamber (part at first and later all) in the piston. There was a new crank at the time too they could have done what was needed but you may be close to the mark that it was cheaper to make 3 new patterns for the caps. I am uncertain if the 1300 had the square caps but I believe that I have read that they were on the 711m6015aa blocks. Probably just cheaper to make all one style.

A lot of the FF guys problems are to do with the flywheel that was required (rules) to be stock and was large in diameter and heavy (13.16Kg Flywheel and Clutch assy including all mounting bolts), thats over 29 pounds. When engines were cheap and readilly available this wasn't much of a problem but the powers the were in charge kept the problem there until just recently when the SCCA alowed a weight reduction of 2 to 4 pounds (some minor amount). At that weight, that is still a lot of mass to spinn at 7300 and that doesn't account for the diameter of the flywheel. When the engine is run as low as it is in FF it is fairly easy to get the flywheel to strike the pavement, its not usually long after that the end is met with Catastrophic results. Yes, life in engineering often involves bandaid fixes that live on for a long time until folks forget why there was a bandaid in the first place, I think that is where we are at this moment. I don't want this question to pop up again as to "why do I need to change the caps?" so I will beat it to ugly death right now.

Gary

I found this Escort twin cam add on Glenn Wallace's web page dated 1968

http://glenn.drizzlehosting.com/twink/ads.htm

and one of the options at the time were Steel mail caps that were to eliminate crankshaft whip part number CD/6000/1

May I add a couple of pictures to the debate on early maincaps? These show,with the aid of red dye penetrant, a failing centre main cap from a 120E block 1500GT motor fitted with a 4-bolt crank and 116E(IIRC) connecting rods that use the smaller diameter cap retaining bolts. The car it was removed from had covered in excess of 100000 miles, and the engine still had the original carb,manifolds and camshaft. The block is bored +0.060", the crank ground 10 thou under on both mains and big ends.

Cheers, Brian.

I'm overdue on an update

The good news is we are getting close to having an engine. While the process has taken much longer than anticipated, I am satisfied with how the build is coming along. that said , looking iffy on getting this off the dyno and in the car in time for October's LOG .

George

+1 with Rohan... find a set of the cast 711M caps, machine some off the joint face and hone to standard size... The cast 711M caps are much easier to machine than the steel caps... the steel cap tends to push the cutter into the softer iron of the block.. should not be a problem for a good machine shop but most would prefere to machine like materials.
Have taken one twincam apart with round caps to have the center cap fall into two pieces.. this was an early 4-bolt engine. I race season... perhaps the driver liked to rev it... or missed a few gear changes..will never know.

Hi,

When I stripped my stromberg road engine one of the main caps fell in half - its hard to believe they would survive in a racing engine.

Regards
Steve

I took the engine off the dyno yesterday and started the prep for installation into the car - The readings from the last session were within 10% of a full race fia motor ( to the low side - we are running lower CR, alternator and tested with the exhaust/muffler in place) , I did not see the point in tweaking it more as it is not a track only car. The decision was taken to run it for awhile and see how it does before looking for more power.
Finished product -

George,
I see you have one of the oil pumps that John McCoy has been developing. Where are you feeding oil back into the galleries? Are you going into the port on the short gallery on the carb side of the block where the pressure sensor normally is fitted? I noticed that the new blocks from Ford Racing have a boss on the exhaust side for feeding the long gallery allowing the cross drilling to be bypassed.
Russ

Hi George
What are the torque and power curves?
Cheers
Dave Hughes
26-R-9

How's this motor going George?