Jump to content
SAU Community

Recommended Posts

So....what is wrong with my RB26?

Recently rebuilt by a engine builder with very suspect abilities. Completed 2000klm since rebuild including 4 oil changes. Running standard computer and standard boost. Rev limit is 8500.

Last 1000klm since running in finished have been a practice day at Wakefiled Park, a race meet at Oran Park and a race meet at Wakefield. In the last race at wakefeild I heard a knock on the last lap, finished the cool down lap and parked it.

The problem - there is a knock/tap in the motor. rises with revs

Oil pressure is normal (great)

Compression test results:

# - Dry test - wet test

1 - 10.5 kg/cm2 - 12.5 kg/cm2

2 - 12 kg/cm2 - 14 kg/cm2

3 - 12 kg/cm2 - 14 kg/cm2

4 - 12 kg/cm2 - 14 kg/cm2

5 - 12 kg/cm2 - 14 kg/cm2

6 - 11.5 kg/cm2 - 13.5 kg/cm2

Battery was boosted by a running car, engine was dead cold. No leakdown test

The noise sounds like it is coming from the top of the motor, maybe at the front or maybe I am imagining it. I put a screwdriver on the head next to my ear, and looked like a person with a screwdriver in my ear.

Anyway....lets have some educated guesses about what is wrong...answers to come sometime in the next few weeks when I get around to pulling it out.

Link to comment
https://www.sau.com.au/forums/topic/89720-what-is-wrong-with-my-rb26/
Share on other sites

  • Replies 59
  • Created
  • Last Reply

Top Posters In This Topic

Duncan ,

It doesn't sound good mate , at a guess ( wild one at that ) i would say its a big and bearing , usualy one at the rear ( number 6 ) but you have a built engine so who knows if they checked clearances or not when they assembled it .

Compression on number one is very suss for a built engine as well as number 6 .

when you say wet test ai would assume you mean you put oil in the cil and heaps of it by the look of the resaults .

The comp test shoul be done on a warm engine and the throttle fully open .

Do a leakdown test it will give you a bit more info ( more reliable ) .

Does the knock get louder as it warms up ? Is it there when you first start it cold ?It could be a lifter or even an injector but my money is on a big end , but i hope i'm wrong .

yeah I wasn't shy with the oil....

Will actually get hold of a leak down tester at some stage but it wont help decide if I have a head or ring problem will it?

The knock is there from cold, not noticably noisier when warm. But I didn't run it up to temp today I dont want to do any further damage.

Bearing clearances were checked at the rebuild and they suggested standard size bearings which i was a bit surprised about I thought an older crank that had been machined might need oversize bearings. Unfortunately I didn't measure the clearances myself :)

Injector is interesting....when can an injector get noisey? I might throw another one in and see if there is any difference to the noise.

What can fail in a lifter? got any pics to edumacate me?

yeah I wasn't shy with the oil....

Will actually get hold of a leak down tester at some stage but it wont help decide if I have a head or ring problem will it?

The knock is there from cold, not noticably noisier when warm.  But I didn't run it up to temp today I dont want to do any further damage.

Bearing clearances were checked at the rebuild and they suggested standard size bearings which i was a bit surprised about I thought an older crank that had been machined might need oversize bearings.  Unfortunately I didn't measure the clearances myself :)

Injector is interesting....when can an injector get noisey? I might throw another one in and see if there is any difference to the noise.

What can fail in a lifter? got any pics to edumacate me?

I have a leakdown tester but you will need a compressor to do the test , i can do for you if you like and i maybe able to give you a more educated guess as to whats wrong with it .

If its a bearing you will do more damage to the crank by running it but if you pulle it out you should change the crank with a new one anyway , if you spin the bearing then conrod through the block is possible .

If the crank was machined they would have used undersize bearings .

Injector can be noisy warm or cold .

A lifter can be come noisy when the clearances grow , there nothing wrong with the lifter , just bigger clearance . you can check with a filler gauge but you need to take the rocker covers off .

The lower comp on the 2 cil maybe because they had the valve clearances to tight ( to have a quiet engine ) and the valves are starting to burn a little .

Did you check comp before ?

You are correct in saying a leakdown test wont tell you if it leaks for valves or rings but it will still tell you more than a comp test .

To much oil in the cil thats the reason comp went up so much ( you made the combustion chamber smaller ( like having higher comp ratio ) .

Edited by wrxhoon
Did you check for woodpeckers inside before u put the block back together? Hope it's not anything serious :)

BTW this was funny....but I didn't post it.....SAU stuffing up or have I been ha><0r3d?

Duncan ,

I just thought of another possibility , just make things abit more complex , could be a gudgeon pin as well , depending on what they used , pistons and circlips or spirolocks , one of them may have come off !!! Then the knock you hear could be the gudgeon pin hiting the bore , you said it sounds like coming from the front didnt you ? That will explain the lower comp on number one as well , the circlip could have scored the bore .

Hard to say without hearing it and knowing how / what they used in the build .

i can say with certainty that it's not a big end bearing... i would definately look into the woodpecker idea though. they can make a noise quite similar to bearing knock as their beaks aren't compatible with the cast iron RB block...

also, could be tinitis from standing around Niels race car or other hearing damage caused be the screwdriver in your ear (you did put the handle in you ear right?) or a combination of the two problems. and actually you have no problem at all. except for the permenantly damaged hearing which is preferable to another RB26 rebuild...

feel better duncan?

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Similar Content

  • Latest Posts

    • Have a look at that (shitty) pic I posted. You can see AN -4 braided line coming to a -4 to 1/8 BSPT adapter, into a 1/8 BSPT T piece. The Haltech pressure sender is screwed into the long arm of the sender and factory sender (pre your pic) into the T side. You can also see the cable tie holding the whole contraption in place. Is it better than mounting the sender direct to your engine fitting......yes because it removes that vibration as the engine revs out 50 times every lap and that factory sender is pretty big. Is it necessary for you......well I've got no idea, I just don't like something important failing twice so over-engineer it to the moon!
    • Yup. You can get creative and make a sort of "bracket" with cable ties. Put 2 around the sender with a third passing underneath them strapped down against the sender. Then that third one is able to be passed through some hole at right angles to the orientation of the sender. Or some variation on the theme. Yes.... ummm, with caveats? I mean, the sender is BSP and you would likely have AN stuff on the hose, so yes, there would be the adapter you mention. But the block end will either be 1/8 NPT if that thread is still OK in there, or you can drill and tap it out to 1/4 BSP or NPT and use appropriate adapter there. As it stands, your mention of 1/8 BSPT male seems... wrong for the 1/8 NPT female it has to go into. The hose will be better, because even with the bush, the mass of the sender will be "hanging" off a hard threaded connection and will add some stress/strain to that. It might fail in the future. The hose eliminates almost all such risk - but adds in several more threaded connections to leak from! It really should be tapered, but it looks very long in that photo with no taper visible. If you have it in hand you should be able to see if it tapered or not. There technically is no possibility of a mechanical seal with a parallel male in a parallel female, so it is hard to believe that it is parallel male, but weirder things have happened. Maybe it's meant to seat on some surface when screwed in on the original installation? Anyway, at that thread size, parallel in parallel, with tape and goop, will seal just fine.
    • How do you propose I cable tie this: To something securely? Is it really just a case of finding a couple of holes and ziptying it there so it never goes flying or starts dangling around, more or less? Then run a 1/8 BSP Female to [hose adapter of choice?/AN?] and then the opposing fitting at the bush-into-oil-block end? being the hose-into-realistically likely a 1/8 BSPT male) Is this going to provide any real benefit over using a stainless/steel 1/4 to 1/8 BSPT reducing bush? I am making the assumption the OEM sender is BSPT not BSPP/BSP
    • I fashioned a ramp out of a couple of pieces of 140x35 lumber, to get the bumper up slightly, and then one of these is what I use
    • I wouldn't worry about dissimilar metal corrosion, should you just buy/make a steel replacement. There will be thread tape and sealant compound between the metals. The few little spots where they touch each other will be deep inside the joint, unable to get wet. And the alloy block is much much larger than a small steel fitting, so there is plenty of "sacrificial" capacity there. Any bush you put in there will be dissimilar anyway. Either steel or brass. Maybe stainless. All of them are different to the other parts in the chain. But what I said above still applies.
×
×
  • Create New...