924Board.org

Dutch924-racer · Joined: 23 Jul 2007 Posts: 1081 Location: The Netherlands

I have had a lot troubles with my last (no.4) connecting rod bearing.

For the second time now (after grinding the crankshaft and new bearings) my last connecting rod bearing has gone. It has spin in the connecting rod and melted.

Is this a common problem ? What could be wrong ? I also replace the oilpump.
_________________
937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

924RACR · Posted: Tue Oct 16, 2007 12:15 am Post subject:

I haven't yet had a failure of that bearing (knock on wood)...

Are you using an oil accumulator (Accusump)? Anything else inside the engine to control oil flow? What bearing clearance are you using?
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

Dutch924-racer · Joined: 23 Jul 2007 Posts: 1081 Location: The Netherlands

No I am not using a oil accumulator or anything else to control the oil flow. do you use that ?

The oil I use is 20W50 Valvoline racing oil.

I don't know about bearing clearance. They use the sizes in the Haney manual.
_________________
937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

924RACR · Posted: Tue Oct 16, 2007 9:52 am Post subject:

I do, yes, I use an accusump and a crank scraper (from www.crank-scrapers.com). I've been using the straight 40W Valvoline race oil, but you should be fine with the 20W50 too - it's good stuff.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

924RACR · Posted: Tue Oct 16, 2007 9:48 pm Post subject:

How long are the bearings lasting for you? How high of an engine speed do you shift at?
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

RC · Joined: 25 Mar 2007 Posts: 2637 Location: Australia

Sounds like your rod`s big end bore is elongated and not providing sufficient crush to retain the bearing. Suggest having all your rods resized or at least replacing that one and having the tolerances checked by a good machine shop.

Roger

Dutch924-racer · Joined: 23 Jul 2007 Posts: 1081 Location: The Netherlands

Bearings last about 30 minutes of racing. I shift just before red.

Can you tell me more about oil accumulator (Accusump) pictures ?
_________________
937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

924RACR · Posted: Thu Oct 18, 2007 9:59 pm Post subject:

Oh, my, yeah, OK, that's definitely got to be an assembly/dimensional problem, not the oiling problems that would be helped by an accusump or crank scraper, etc.

If you haven't replaced that one rod, it definitely won't last - it's got to be bad. I'd never re-use a rod that spun a bearing, at least not without having it re-sized, like Roger said.

Shift points - I always shift at 6000rpm, unless I'm mid-pass going to the checkered flag! There's no more torque above that point, and it really adds to the strain, especially seems to hurt the valve stem seals. So I'd recommend easing back your shift point, it should help engine longevity noticeably.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

Dutch924-racer · Joined: 23 Jul 2007 Posts: 1081 Location: The Netherlands

I brought the crankshaft to the grinding shop.

What can I change about the carter so I don't have this problem twice ?
_________________
937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

PORSCHEV · Posted: Mon Oct 22, 2007 8:04 pm Post subject:

If you only took the crank to be checked ..make sure you also have the connecting rod checked as well. Thats more likely what is out of round.
_________________
1976 924
5 lug conversion, 17'C2 wheels,custom body work,327 vette engine.

1978-#53 "D" track racer.

Dutch924-racer · Joined: 23 Jul 2007 Posts: 1081 Location: The Netherlands

Crank has been machined to 0.50.
I am now looking for replacement connecting rod, the old one can not be used anymore as the bearing spun in it.

old bearing, that spun around in de connecting rod.

New old stock bearings (hard to find in the Netherlands)

_________________
937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

924RACR · Posted: Sat Oct 27, 2007 7:16 am Post subject:

Ah, fun... yeah, that's what mine looked like when I spun bearings. Had to replace the crank and rod both.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

PORSCHEV · Posted: Sat Oct 27, 2007 10:01 pm Post subject:

Did they machine all the rod journals down by .50? It might have been easier to find another crank then over sized rod bearings

_________________
1976 924
5 lug conversion, 17'C2 wheels,custom body work,327 vette engine.

1978-#53 "D" track racer.

Dutch924-racer · Joined: 23 Jul 2007 Posts: 1081 Location: The Netherlands

Engine rebuilt is almost finished, I will post some picture tomorrow. I have the next race 3 november.

Hope it will last, if not I will sell the car

_________________
937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

Nobbi · Joined: 24 Aug 2006 Posts: 1396 Location: Germany

Hello,

where is that race takeing place? i like to take a look!

Nobbi