Rebuild time (part 2)

[bruceb]

Well I finally got to survey the carnage caused by the cam chain tensioner failure. The motor is completely stripped at BW's

 

Here are some scary pictures of the failed piston, and another piston that has been hit by an inlet valve. Thats about it for gory piccies, the rest of the engine is in good nick which is a real relief.

 

The valve hitting piston is clearly down to the tensioner failure. The cause of the piston breaking up is not really clear. The only thing that could be determined for sure is that the chunk of piston below the oil control ring broke away suddenly as the fracture was clean and showed no sign of fatigue. My guess is that the oil ring end gap closed up for some reason and then the ring dragged on the cylinder and loaded up the wekest part of the pistion until it broke. So its six new pistons for piece of mind

 

amazingly all six cylinder barrels have zero measurable wear or scoring and are good to go with new pistons

 

The crank is showing no signs of wear and measures well within tolerance and only requires a slight polish to the journals

 

The cylinder heads show no visible damage from the one inlet valve hitting the piston.

 

At the moment I am waiting for BW to confirm some special pricing to put it all back together again. Until then, no firm ideas as to what to do next, however:

 

Rebuild (part 1) saw 235bhp at 6500rpm which made for a great trackday motor

 

Rebuild (part 2) has the ambition, it not necessarily the funds, for peak power around 6800-7000rpm to make an even greater track day motor, sure to keep up with any more 3.6 conversions

Edited September 28, 2007 by bruceb

[GaryH]

Ouch mate - hurts just to look at that piston !

 

Go on - higher rpms, you know you want to !!!

[pete917]

that looks really painful! Are you putting stock pistons back or something a bit special?

[bruceb]

Hey I just went overt to the PP engine rebuild forum an guess what, a thread full of pistons that look like mine

 

http://forums.pelicanparts.com/showthread.php?t=369157

 

So it looks like detonaton caused the piston to fail..........ho hum

[JezHill]

Chin up Bruce

 

You know you wanted more power, this is just God's way of making sure you got round to doing it

[johndglynn]

So it looks like detonaton caused the piston to fail..........ho hum

Are you sure about that? Henry's reply in the other linked thread seems to suggest it is poor fuel and too-high compression that caused it, saying he limits all CIS motors to 9:5 to 1.

 

OK I'm no expert but I never heard any pinging in your motor, maybe I wasn't driving it hard enough, but even when you were driving I couldn't hear it. How does det cause a skirt to collapse?

 

Glad my timing is stock if that is what happens.

[bruceb]

No I never heard any pinging either JG.

 

The engine had done 5000 miles and 9 trackdays since the rebuild so it would seem to be a problem that takes time to develope.

 

I found this on the Rennsportsystems site:

 

" Since engines are inherently noisy and air-cooled engines in particular, are somewhat noisy due to fan, valve gear and chain noise as well as having no water jackets to dampen engine sounds, it is very difficult to hear low levels of detonation in these cars. In addition, there exists a phenomenon known as sub-audible detonation. This condition can occur in any engine and is very dangerous since it is almost impossible to detect except by careful spark plug inspection. The engine can be detonating and you may never hear anything. Spark plug center insulators have been known to shatter and broken rings are found from this phenomenon without the driver being aware of any additional or unusual noises.

Sub-audible detonation can burn holes in pistons and destroy ring lands before anything is noticed."

 

If this is what caused the piston failure then at least its an explanation and there is stuff to be done to prevent it the rebuild.

[bruceb]

I'm close to getting the rebuild underway and need to start spending some dosh on some new parts.

 

As my pistons are kaput I need to replace them, or buy new Mahle P & C'c ( $$ ouch).

 

The two least expensive options for the rebuild using new parts appear to be either:-

 

3.0 JE Pistons and Twin plug ignition

 

or

 

3.2 SS using Andial CIS compatible pistons and single plug

 

 

Getting a reliable engine is the most important consideration, what to do?

[oliverjamesthomas]

For my two penneth, I'd vote for a 3.2SS and single plug. It'll be a screamer of an engine and you don't have the expense of the twin plug scenario to consider.

 

Get some weight off the flywheel, (if you haven't already) and you'll have one hell of a car

[bruceb]

At long last the engine rebuild has started

 

With a bit of luck it should be completed by the end of November, providing ACE stops bleedin queue jumping

 

After mucho pondering of all the options, I decided to keep the engine in 3.o form with the rebuild spec like this:-

 

Tuthill spec lightweight JE pistons

Clewett crankfire twin plug

approx 10.3:1 cr

Boatailed crankcase

DC20 cams (as before)

Bottom end balance

Running in on the rolling road

 

In this spec I am hoping to get about the same power as before which is approx 235 bhp 6500rpm with the CIS.

 

Later on when funds permit the engine wil get some really nice cams, such as GE60's, Jenvey ITB's and an ECU, for an estimated 270-280 bhp

 

I eventually gave up trying to wade through the Bob Watson after sales sevice and have now taken the car plus a completely stripped engine in about six cardboard boxes over to Harvey racing. They have offered a very competitive price to put it all back together, what a relief

[topcarrera]

Good news Bruce - I hear the Harveys build strong engines and that they RDKTO's.

 

Better luck this time and looking forward to more exciting pax laps soon!

[MrPerkles]

hope it all turns out ok Bruce and it goes like stink

[johndglynn]

Good job Brucie, shame things didn't work out with BW but I think you will come away with slightly more than you are hoping for.

[jevvy]

Progress at last thanks for the update.

 

Bruce + 270bhp = broken passenger door handle, you may need to upgrade that before the ITB's

[carlbon]

With a bit of luck it should be completed by the end of November, providing ACE stops bleedin queue jumping

Well done Bruce

IB are putting a lot of work the Harvey's way at the moment

They are building me a 3.2 engine, and another friend is having RS suspension & geometry fitted to his 964 by them

[bruceb]

Here a few piccies of the engine whilst apart and some top and bottom views of the new lightweight Tuts JE pistons.

 

Big end bearings looking good with 95k miles on them, but they wil be replaced anyway

 

Big end and main bearing journals all within specification

 

Underside of new piston looks nice and strong

 

 

piston crown has large valve pockets for a greater choice of camshafts

 

Edited November 4, 2007 by bruceb

[Sean_IRL]

Are you telling me you did those laps in silverstone on a dodgy engine

 

Happy too hear you're progressing on the new rebuild.....and look forard to seeing more shiny C & P's.

 

Wheres the default pic of your engine block at home....doesn't everybody do this??

 

[SP72]

Underside of new piston looks nice and strong

 

piston crown has large valve pockets for a greater choice of camshafts

Bruce

 

what is it about the JE pistons that make them 'Tuts'? Are they any better suited for long term use, which is often doubted on Pelican? eg Steve Weiner

 

Shirish

[johndglynn]

what is it about the JE pistons that make them 'Tuts'?

They are build to Tuts own spec. They're in 4 Tuts engines now so we'll see how they last.

[SP72]

They are build to Tuts own spec. They're in 4 Tuts engines now so we'll see how they last.

Cheers john, these road or race engines?

[johndglynn]

Cheers john, these road or race engines?

Engines that require reliability mate.

 

The JEs are pretty much half the price of their Cosworth pistons, and I just bought a load of 3.2 bits to build with - case, heads, pistons, cylinders, rods etc. Will prob go for the JEs also.

[bruceb]

There has been some questions raised on pelican with JE's. I did a truck load of searches and found a few instances of problems in high spec race engines from a few years back.

 

For the road there seemd to be some old concerns with increased noise until the engine is warm and that was about it.

 

I have had the pistons measured and compared them with the Mahles. The Mahles are the same diameter from piston crown to the bottom of the skirt.

 

Interestingly the JE's are exactly the same diameter, but the area above the top ring is relieved by 0.5mm and this explains how they have been able to reduce the overal running clearances and reduce noise on cold starts.

 

So my reckonong from the data is that these pistons will make no more noise than the mahles, we will soon see! They should also last better as they are forged compared with the cast mahles and of course they are lighter.

 

A few weeks back I compared the JE side by side with the Cosworth piston and there seemed little between them visually although structurally the cosworths looked to be a bit stronger still. So for my realtivly low stressed motor the JE's were the choice at half the price of cosworth pistons.

[strosek34]

Observations:-

 

The walls on the piston top to the right and left of the valve pocket cut-outs look quite thin to me,

aren't they liable to cause hot spots there,

 

I am also surprised they don't have more radii on the cut-outs for stress relief.

 

Going to be a great motor when its finished Bruce.

[johndglynn]

Have to say I am looking forward to this build very much. The last incarnation was good, this should be brilliant.

[Richard Bernau]

Observations:-

 

The walls on the piston top to the right and left of the valve pocket cut-outs look quite thin to me,

aren't they liable to cause hot spots there,

 

I am also surprised they don't have more radii on the cut-outs for stress relief.

 

Looks that way doesn't it. Does your engine builder deburr (or whatever the term is) the sharp edges?

 

You can certainly see why you need to twin plug with that shape of crown.