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My reluctance to a procedure that hasn't been tested is opinion. It is not a personal or being critical. You may have a different opinion, be willing to to it and test it, and report results. Great, I will listen.
I bought stuff from Lindsey because it is tested and proven according to Dave. My homework backs up his thoughts about his products and applications. Given what has been spent on the motor, by the p.o., and myself, I choose not to pull the trigger on this modification. That is my choice, you are welcome to another, that is yours. Good luck.
Sarcasm and personal comments just don't make sense here.
So the timing belt finally thought it was time to test my conversion to a non-interference engine, by snapping about 10 miles from home.
I don’t think the belt had done more than 20k miles and maybe 2 years ago I re-tensioned it by letting the auto-tensioner set the tension. It may have been too tight, since there lately had been slight belt whining, which I deliberately ignored. I now wonder what the thermal expansion of the belt is relative to aluminum, since the tension may have been set on a hot day and the break happened on a cold morning.
The result: An inconvenient AAA tow home, $20 belt expense, some hours of belt installation time (slightly looser than before) and best of all, no change in performance.
In other words the conversion worked as intended.
I now wonder what the thermal expansion of the belt is relative to aluminum,
Check the belt tension with the engine cold and than do the same with the engine at working temp. Modern belts or waterpumps shouldn't fail below 40k/5 years. I use the waterpump pulley twist method to to tension the belt.
I am certain that the killer of belts on our motors is the non-compensating tensioner, which doesn't have allowance for belt stretch/contraction vs temperature. Even the "auto tensioner" is a locked, manual tensioner when tightened down.
On the 968 which has a dynamic tensioner Porsche raised the belt interval to 60k miles over the 944 30k/45k depending on year.
I think I've figured a way to make a hydraulic tensioner out of the standard 944 auto tensioner swing-arm but haven't had a chance to test it...whenever I get around to putting another engine together I'll try it out.
Would your jig be able to convert NA pistons? I have a set from my project engine sitting on the bench. I was thinking this, plus a Swaintech coating on the tops to insure against hotspots.
All you're hard work payed off and what are the odds of that actually happening to you?
I enhanced the odds, but ignoring the belt's audible "complaints".
Originally Posted by odonnell
Would your jig be able to convert NA pistons? I have a set from my project engine sitting on the bench. I was thinking this, plus a Swaintech coating on the tops to insure against hotspots.
I have only done the numbers, measurements and assessments for the standard turbo pistons and would think that too much material needs to be removed from the N/A pistons.
I'd have the same concern as adrial (hotspots) - the other would be cost. These things would be ungodly expensive to make and then have coated to be compatible with the alusil blocks. As an alternative that would possibly preserve compression would be to dome or "flat top" the piston with the cut-outs for the valves. One would partially offset the other.
I have been researching the possibility of converting an interference to non interference to prevent the broken timing belt valve destruction catastrophe. I came across this forum and realized that there was an 11 year gap between comments. Im glad the modification worked for you Laude Pederson. I had thought about doing this to a Volvo 5 cylinder turbo engine. I admire that you posted the results after more than a decade.
Bumped into this thread after reading through another looking for another topic (scope creep in reading is a b!tch).
Noted others have had success with flycutting the pistons that were used in a 2.5L 16V (Raceboy). Curious if anyone taken this road since then? Looking for your testimony.
I had Mike at Lindsey make me a set of custom JE pistons for my race engine ... we specifically decided to make the valve pockets deeper due to the Milledge
high lift cam i was using as well as the particular head ( ported and cut down .030 ) i was using for the first engine.The pistons are fairly high compression ... i won't get into details but they do have a 3cc dome and the engine made pretty good power.Anyhow , since i'm currently building another race engine , the pistons are out, i can post a side by side picture of my pistons and a stock one
if you wish.
The engine revs and makes power until 6900 rpms on the dyno, my cutoff is at 6700 , so valve relief was critical , will eventually be looking at better valve springs than the new turbo units
i have in the fresh head i'm using for this build.
02-23-2005, 01:42 PM
