grrrmonster

How often should a 997.1 GT3 motor be refreshed? At a tech session this morning they had several GT3 motors apart. Connecting rod issues with heavily tracked cars. Big und of the rod getting stretched and becoming oblong. Causes bearing to spin inside the rid, drops oil pressure. Discoloration on short end of rids and small cracks starting to show from stresses.

Freaked me out. Anyone have insights on longevity and expected life?

MC 968CS

There's a key question to ask re those rods. Had the engine been significantly over revved. Eg on downshift.

I'm suspecting yes. Therefore ...Stretched rods

grrrmonster

Three motors! One shop.

extanker

to-days safety tip.....do not stretch your rod .....it could hurt...........

Izzone

Rods time out, on all cars

LIS

What shop was this? I'm looking for a decent pcar shop in/near Pittsburgh.

grrrmonster

Depends what you looking for. If an indie shop- check out George Riggin Specialty Auto in Harmony, PA north of pittsburgh. If you want a dealer- SEWICKLEY Porsche (Duane Smith is service mgr)

LIS

Thanks, I'll check them both out. Been using an indie for most work that I can't do myself, but not opposed to the dealer if they're good.

Macster

Longevity and expected life is a roll of the dice. Some sources report engine rebuilds after 50 hours track time. Others after 100 hours. Others much longer intervals, not measured in track or running time but in tens of thousands of miles covered.


Because titanium rods can stretch, if one is using aftermarket rods the rod maker should offer some guidance as to when the rods should be replaced.

If there is no guidance then there is careful monitoring of the oil pressure at a known oil temperature. When one notices the oil pressure lower at a given temperature that is a sign of clearances opening up which is a sign it it time to open the engine up and do a refresh.

Oil analysis might also provide a clue if bearing metal PPM numbers go up. The analysis should be done in a consistent manner, after so much track time.

Spyerx

no need to worry guys.
my shop probably builds as many mezger motors as anyone (like several at a time in build), cup motors, street GT motors, turbo motors.
The TI rods stretch yes. The cup motors, 100 hours you start to see 'issues' but they can go longer if you're not up over the limiter every shift.
And yes bearings wear, etc.
When it's time to rebuild/refresh, replace the rods with steel, proper ones are lighter and stronger than the TI.
Do oil checks, change oil a lot, don't over-rev, etc. Your car will be fine, but mechanical parts do wear!

BTW, shop had a .2 GT3 in for a refresh, car had a mechanical over-rev (range 3 I think??), but the issue was it backed the bolts out on the cam adjuster, wore the case, got metal everywhere, etc. So the only "issue" from the rev was the actuator case problem, but that got metal into everything, and scored bearings. So this owner got new cam actuators, new bearings, and had to have the entire setup cleaned due to the metal. Not a cheap job. Not a lot of parts, bearings, but also some 'while int here' stuff they do on all motors they open, but a lot of labor.

m42racer

All rod BE's go out of round. The bolt gets stressed which causes the clamping on the bearing to change and causes the loss of oil clearance and the results you saw. Sure Ti rods need attention a little more than steel rods maybe, and this applies to the other end of the rod as well, but a steel rod needs attention too.

To imply that a same size steel rod would be better and lighter is not correct. Not sure what Ti rod that person had used but to think that any steel rod is lighter than the stock GT3 rod is wrong. Steel rods are fitted to these engines for one reason only. Cost of replacement Ti Rods.

Owners are duped into thinking that they are getting something better with a steel rod. Nothing could be further from the truth. The extra weight of a steel rod changes the dynamic of the engine. The rotating masses change along with all of the kinematics of the engine internals.

The cracking could be from the bearing losing its clamping and any pick up on the rod BE inner diameter would be from the steel backing of the bearing.

I have never seen a Ti rod fail due to its material in a GT3 engine. My guess would be that these engines were abused and a steel rod would probably look the same.

Another point that needs to be made is these crank twist from harmonics. This is well proven. Because of the stroke the overlap is a lot less and the Rod journal diameter is smaller too. These high frequency vibrations cause all sorts of damage. As the cranks twist back and forth the bearing oil clearances can change and the BE of the rods also get forced out of round. Remember we are talking about 0.0018- 0.0028" overall clearance so the rod pin doesn't have to change much to lose it clearance.

As the other person also stated about another engine that failed, the Cam actuators absorb all the same vibrations which is the case of the bolts backing out. Your cam timing is all over the place as well, and there goes performance.

m42racer

How often should a GT3 engine be rebuilt?

There is no time unless you want to work on the premise of engine risk management. Abuse and lack of servicing will shorten the engines life. A race engine that is respected for what it is will get regular service and probably rebuilt on a hour basis. This is dome to ensure that all internal parts are at their best condition always.

However, this typically is never the case in club racing or street engines used on the track. The engine is the ugly step child and usually is forgotten about until it screams "Im hurt". Cars get new tires, new paint and stickers and other appendages to make them look faster and the driver gets a new fancy helmet and patches on his driving suit.

If you look after your engine and drive within your capabilities, service the engine regularly, monitor the compression and or leak numbers you can run as long as all of these look acceptable. These engines have a couple of issues that will appear at some point in time. Valve guide wear which results in Valve seat sealing is problematic. You can monitor crank case pressure as well and as soon as this starts to go positive above an acceptable value then its time to rebuild. Then, all internal parts including the rods should be rebuilt to spec.

So its down to your ability to look after your engine and it will tell you when its time to rebuild.

MJSpeed

We've done three 4.15L builds recently and and none of them had any stretched rods. They're Ti and they will stretch when "abused."

Over a year ago we did one which did have stretched rods. However, that one had been used very harshly.

Those who look after their engines and maintain them methodically and meticulously, generally speaking fair much better.