floatingkiwi

Hi All

My 944 S2 race car is breaking valve springs. It has done it before and seems to have done so again. Last time it had a full set of lindsey racing springs put in. The engine has standard cams, and no chip so a standard rev limiter as well. The engine is standard S2.

I've checked the balance shafts and they are OK, haven't skipped a tooth.

Any ideas?

V2Rocket

Is the same spring(s) breaking repeatedly or different ones each time?

928motorsports sells a high-performance replacement single spring "beehive" set you could use.

floatingkiwi

I'm not sure which have broken before, but I have learnt that it was fitted with a full set of 2 piece springs from Lindsey racing when rebuilt 4 years ago. Those springs were not Porsche, and Lindsey are not doing that type any more.
So my options are Porsche springs or yes, maybe those beehive ones. The only thing is that with 2 piece springs if you break one you wont drop a valve but what happens if one of the beehive ones breaks? I don't know.

951and944S

Do you have a picture of one complete set of broken parts from just one cylinder..?

From the keeper down to the shim, let me see what was installed.

T

V2Rocket

thinking too many shims or wrong bottom cup, T?

the 944S/S2 springs are not very "stiff" spring rate and they aren't working super hard with the mild stock cams. so breaking would make me think they are binding at some point.

951and944S

Could be bind, but the spring data sheet on the Lindsey supplied springs (from memory) lists an allowable lift before coil bind and the stock cams are nowhere near max.

That's assuming, as you say, that they are shimmed correctly.

If I had to guess, the hardened lower spring support was deleted.

Controversial maybe, but springs and valves rotate at high rpm (track tach range) through frictional transfer of torque when the valve is unseated. If the spring doesn't have a hardened surface to break friction with a knurled or soft shim or bare aluminum spring pocket, depending on direction of coil winding, the spring can either coil or uncoil itself, shrinking (interference with inner) or growing (unlimited stress that causes failure) of it's static diameter.

If a picture were presented that showed proper hardware, I'd have to say defective batches of springs are possible.....it happens.

T

951and944S

T

(If videos won't show, will delete)

michaelmount123

The stock Porsche valve springs are very high quality; far better than any of the aftermarket springs. If you replace what you have with S2 springs and make sure they are installed at the correct height spec, your problems will be history.

floatingkiwi

Thanks guys - I wont be pulling them out until I get the new lot, and I probably will be going stock S2.


michaelmout123 - height spec??

951and944S

+16...

Went down this road on an 8V race engine, lost two cylinder heads and whatever partial travel and expenses from Baton Rouge to Sebring, plus a predicted enduro win for my son.

Went back to stock springs, never had another problem.

T

951and944S

You may need some items that have been discarded so you won't know unless an inventory is taken in teardown.

Also possible that the springs beat up the cylinder head to the point where it may be unusable or at least damaged the guides.

If you have aluminum damage, pieces of valve stem seals or parts of the broken springs that can't be accounted for, at a minimum, I'd drop and clean the pan, check the bearings and replace the oil cooler.

Shop run engine on less expensive oil with a new filter at 2000 rpms for 15-20 minutes then drain hot, replace filter again and add your track oil brand.

T

floatingkiwi

I have 2 options for springs, from design911. "OEM" springs and the proper Porsche springs at almost twice the price. http://www.design911.co.uk/fu/prod42...7-94410590703/

floatingkiwi

For the correct height spec, my guy says he puts compressed air in the cylinders and changes the springs like that and so can't adjust the height?

400hp944

Had the same issue with my 944 Spec race car. Bought Porsche springs direct from Germany a couple of years ago and no more problems.