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Rb26 Compression With Poncams Type-B

andre_gtr

By andre_gtr,
in Engines & Forced Induction

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Shoota_77 Veteran

Shoota_77

Posted
Posted

Yep same as last few posts. Last step before pulling the engine back out again is mineral oil and provided everything is feeling half ok I'd give it heaps. Heaps of boost and heaps of load. You need to try and undo all the glazing of the bores that idling will have done. Hopefully there is enough cross hatch (you did hone the bores I'm hoping???) to bed the rings in a bit better. As per above you need to force the rings hard out against the bores hence why you want plenty of boost or load to achueve that.

Good luck, it's a bitch to have to pull the engine out again if it's no good!

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SiR_RB
SiR_RB

Idling for 30mins? I was told start up check for leaks then go for a drive with varying loads Minimize idling during run in

GTSBoy
GTSBoy

It's actually funny how the old and sensible instruction to avoid idling a newly built engine coupled with the old and sensible advice to run the engine through a variety of loads and speeds (but not

XKLABA Grand Master

XKLABA

Posted
Posted

This /\ /\

When I built my engine I comp tested at +/- 150psi before starting it, started it and let it run for 5mins, dumped oil refilled with mineral diesel oil, took it out to the M4 did some controlled loading till I got to the mountains then vaired from 3500rpm to 4500rpm as it climbed the hill came back down turned around and did a couple of 2nd gear hill starts at 4000-5500rpm, went home dumped oil and refilled then comp tested at +/- 170psi, a year later it comp tested at the same +/-170psi

AngryRB Grand Master

AngryRB

Posted
Posted (edited)

Which will increase overlap and drop compression.

Why are you worried?

I don't understand why the cams were adjusted, says on the RHDjapan website that they are a drop in cam which

don't need adjustment and if adjusted 1degree will dramatically impact idle and low end torque.

If it affects idle then that means compression test will be crap.

Maybe set the cams to normal position and retest?

Edited by AngryRB
GTSBoy Grand Master

GTSBoy

Posted
Posted

Desperate measures for bedding in rings on an engine that had been accidentally glazed up after a rebuild used to be to tip a tablespoonful of Bon Ami down the carby. I shit you not. Slightly harsh treatment to be sure, but given that it is either that or take it apart and re-hone with new rings......

You could rig the AFM up to a hose onto the TB to bypass the turbo if you were needing to do it to an RBDET.

Piggaz Grand Master

Piggaz

Posted
Posted

I don't understand why the cams were adjusted, says on the RHDjapan website that they are a drop in cam which

don't need adjustment and if adjusted 1degree will dramatically impact idle and low end torque.

If it affects idle then that means compression test will be crap.

drop in means they fit without head mod (shimming doesn't count here). How does Tomei know what the user wants out of his setup?
AngryRB Grand Master

AngryRB

Posted
Posted (edited)

My point was, the maker of the cams suggests that changing the timing of there cams will affect idle and low end

torque, extra duration creates poor combustion efficiency at low rpm, so at 200rpm it would loose a lot of compression on a test if OP has increased the Overlap.

http://www.rhdjapan.com/tomei-camshafts-poncam-rb26dett.html

Edited by AngryRB
XKLABA Grand Master

XKLABA

Posted
Posted

mine is currently +2 intake -4 exhaust

100 psi is very low, what exactly did you change when doing the rebuild, are the cams timed correctly

Those setting should actually increase the compression reading, even if it is only a little bit as they aren't that big of a change

GTRPSI Mentor

GTRPSI

Posted
Posted

You need to lean into the motor gradually and stay away from any synthetic oil for the first few thousand Km.

Load the engine, you need pressure to push the rings onto the bore to bed them, idling does nothing but take the peaks off the hone without bedding in the rings.

I recon go back to a mineral oil and lay into it a bit, hopefully most of the cross hatch should still be there.

Also check your mixtures, if your running rich, expect to see your oil contaminated with petrol, its not a good thing to wash the oil off with fuel on the bores, not a good start to the engines life.

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