Advice on choice of valve springs, retainers and rockers

Litle brother · 02:34 PM

Hi all.

I have a 911 3.2 short stroke engine with 290hp and 247ft lbf. Max power is at approx. 6900rpm. Rev limiter set at 7200rpm.
It was built in 2016 and has the following spec:
- 3.0 SC 204hp engine case, crank and cam towers
- 3.0 SC 180hp heads with 39mm intake ports.
- 3.2 Mahle RSR piston and cylinder.
- Webcam 120/104 "RSR" spec cams.
- Aasco race springs.
- Aasco titan retainers.
- Twin plug.
- PMO 46mm throttle bodies.
- Full sequential ecu.
- Eisenmann exhaust with 39mm primaries and modified muffler.

Engine always driven on good quality oil.

So to the case:
I have issues with wear on some of the rockers and cams I have to address. Other rockers and cam lobes are very good. See this thread:

https://forums.pelicanparts.com/911-engine-rebuilding-forum/1032992-colour-camshaft.html

I know I have to change to new cams and I have been thinking that the Aasco valve springs might be too tough on the cam lobes and thus one of the reasons for the wear I have found. So before I start buying parts I thought I would discuss this with you here on Pelican.

Should I change back to original valve springs and retainers? Can they handle the lift and profile my cams has?

Should I buy new billet cams or hardweld my old ones?

Should I hard weld my old rockers or buy factory new ones, and should the hard weld ones be coated with hard chrome and why(the technical reason)?

What combo of the above or other combos will be the best solution for my engine? And this time it must be durable for many years, obviously.
I do NOT track the car, it is only street driven, though quite inspirated at times.

Perhaps Webcam, Camgrinder, Steve Weiner, other reputable engine builders or you guys can give my good input

Here's the cam and valve spring specs and the wear problems:

Sent from my iPad using Tapatalk

Neil Harvey · 06-26-2019, 04:59 PM

I'll jump in here as this sort of damage is one of my pet peeves.

No complaint about the parts themselves, but in my opinion you have too much spring for your engine. But I do not think the damage was caused by over springing. I think it was probably caused on the initial start up. It looks like there is some scuffing going on but to be fair, it is hard to see in the photos.

These rockers are cast and the material is not the cleanest. The steel has impurities (inclusions). All steel does, but cast often has a lot more. As soon as you put a lot of contact stress on the rocker pad, and do not remove the heat caused by friction, you damage the surface. If under the surface there are inclusions, the surface fractures and without good support beneath, pitting happens.

For a street engine, you should not be using Titanium Retainers. Unless you want to go into the engine and inspect them regularly. Use the stock ones, have then crack checked or use some tool steel types.

I'm not a fan of hard welding cams. Rocker arms can be repaired with hard chrome, but be sure you use a good company that knows what they are doing. Both surfaces cannot be as hard as one another.

Without know the cam details, but just figuring on the engine spec and RPM, with stock valve train components, you should be running about 72- 80 lbs on the seat. The springs you have probably give north of 100 lbs. If all else was good, the seat pressure will hurt the engines performance more than cause this damage. But heavy pressure will wear out parts sooner than lower pressure.

Often the cam design is bad and the over springing is required to control the harmonics the cam design induces into the valve train. Buy decent cams, have the rockers rebuilt and fit springs and retainers suitable for your engine and its use.

Mark Henry · 06-26-2019, 06:01 PM

I have the same cam on my 3.0 with TP and RSR style mahle pistons.
I'm using Eibach sport springs and stock retainers.

Trakrat · 06-27-2019, 06:38 AM

just my 2 cents... I'm going from a 3.2 to a 3.4. I went with Aasco titanium retainers and springs as well with 964 cams and just had my rockers machined at Ollie's.

I talked with the guys at Ollie's about this topic (should I go with titanium retainers and higher strength springs?) and also talked with Aasco and a few others on here.

I too was concerned about added wear from the springs... but, the reason I am rebuilding my engine is because of a minor over-rev that caused my valves to smack my pistons. Lost compression after that.
Everyone I spoke to said that the Aasco solution would have prevented this from happening and that the reliability of higher revs will far outweigh any additional wear and tear on the lobes.

While my car is a 'street' car... I redline it every chance I get on the street and highway, and will probably take my car to a few driving events if I can.

If you are putzin around the city, barely going over 4k rpms, then sure... stick with stock. But if you are planning on having fun and scream through traffic at 7k rpms... then best to go with the Aasco springs and retainers.

Trackrash · Trackrash's Garage

Just to confirm what others have said. With that cam, I believe stock valve springs would be marginal at best. I am guessing Web cam recommends stronger valve springs, like you have.

I can confirm that John D. recommended stronger springs for the high lift cams he provided for me.

In fact he specified 80 pounds seat pressure.

Point is, in your case find out what seat pressure Web cams specifies for those cams. Then measure and install your springs to that spec.

If your rockers had been refinished to the point that the hard surface was compromised it could have contributed to your failure.

BTW, I had my throttle stick wide open at 6K + RPM at an autocross. Only damage was to my front tires.

Neil Harvey · 06-27-2019, 08:55 AM

So would a 400 lbs spring, but would you use that? I guess its a one spring fits all type of thing.

Springs and their characteristics should be selected by what they have to control. Valve train weights, cam profile and for sure, the engines use.

We consider performance like currency. You have to earn it and once we have it, we don't like giving it away.

911pcars · 06-27-2019, 09:30 AM

Neil just mentioned it - valve train weight.
Ti retainers help reduce the weight, but recognize the potential trade off.
Other valve train parts can be addressed as well (valves, rocker arms), but require more investment in time and $$ to achieve that objective.

Contact the cam manufacturer and ask. I recall Webcam recommended new or their rebuilt/treated rocker arms with their products. Something like that.

Sherwood

LukasM · 04-02-2024, 02:32 PM

@Litle brother and all,

What is the current thinking on the AASCO HP springs and ti retainers? Are the stiffer springs really a problem with new cams and/or refinished rockers for a street car?

I don't think many of us are going to put another 100k miles on these cars any more given their increase in value, I know mine is seeing a few thousand miles a year. I'd love to have the overrev protection especially with a hotter cam in a 3.2 to 3.4 or 3.6 to 3.8 build.