Rb26 Compression With Poncams Type-B

[Shoota_77]

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!

[XKLABA]

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]

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 June 11, 2014 by AngryRB

[GTSBoy]

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]

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]

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 June 12, 2014 by AngryRB

[andre_gtr]

Cool thanks guys will give it a bash

[Piggaz]

Has it had the mixtures and timing looked at after being screwed together?

[XKLABA]

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]

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.

[andre_gtr]

Timing has been set and afr are pretty close to what I want them on the map not too rich

it was a total rebuild with old pistons and new rings, honed bores

[andre_gtr]

still running on multigrade mineral oil delo400 should i bump it down to a monograde

[KiwiRS4T]

still running on multigrade mineral oil delo400 should i bump it down to a monograde

Should be fine.

[XKLABA]

What head gasket ?

[Piggaz]

What CR was the engine built to?

Have you checked with a second gauge to confirm the first gauge is accurate?

[andre_gtr]

not sure about these questions head gasket is tomei 1.2mm and stock pistons

[andre_gtr]

no havnt used a second gauge but the gauge reads about 10.5bar on my rb25det

[Sinista32]

Never mind first post. (now deleted and edited)

So your saying the same gauge reads 150psi on your RB25

ok

Edited June 13, 2014 by Sinista32

[andre_gtr]

Never mind first post. (now deleted and edited)

So your saying the same gauge reads 150psi on your RB25

ok

yes thats correct

[Sinista32]

Time to take it for a blat as per the earlier advice given to create pressure to push the rings on to the bore and bed them in

good luck

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