Interesting Outcome - No more blow-by after fitting the reconditioned head

It has been a quite an unexpected surprise for me to find out my RB30 engine
practically show no signs of excessive blow-by after fitting the home reconditioned
cylinder head.
The only reason I can come up with to explain it is the excessive machining the old cylinder head had gone through(1mm beyond the limit set by Nissan for RB30 engine).
The reconditioned head is still within the factory specs.
I'm guessing if the excess compression caused the previous excessive blow-by, then it is logical for me to expect low compression and probably reduced power from the new cylinder head, but that's not the case either.
I think the cam timing was also way out before which must have affected the power out in a negative way. Now the cam timing is back to factory settings has offset any loss of power from drop of compression.

I am pretty impressed.

If you guys have any theories for the disappearance of the annoying excessive blow-by issue I had before, I would love to hear it.

Blow-by was so bad before, I had to basically glue the rocker cover to the head using Permatex Ultragrey and leave it for good twenty four hours to harden the stick. Oil was seeping from the back of the head between rocker cover and head(rocker cover gasket), it only stopped after I used Permatex Ultrgrey.

Now I only have the rocker cover fitted lightly with the rocker cover bolts with the old gasket(no Permatex Ultragrey)

Its about time you started hosting your own home repair youtube channel DOM!!!! Congrats.

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Originally Posted by PeeBee

Its about time you started hosting your own home repair youtube channel DOM!!!! Congrats.

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Thanx Phil. I have a long way to get over my camera shyness. :D
Cheers
Dom

if blowby is reduced after reconditioning the head , i think it would most likely been worn valve guides and valve guide seals that was the culprit and possibly even a leak thru the head gasket to a oil gally (which would normally be self evident when you removed the head). with excessive blowby , this means that effectively power is leaking out of the compression chamber and into the oil chamber and out thru the blowby hose instead of being used to push the piston down to turn the crank shaft ' Ie; reduceing efficiancy if there is little blowby now it would suggest the rings are in good condition. i'm not sure what you mean by "excessive machining" but would take it that the head was machined because it was either slightly warped or slightly damaged. machining it will ensure it will seal better when it is refitted to the block. depending on how much it is machined, it can increase compression to the point the engine will noticeably perform better. t don't now much about rb30's but with carburetted and timed motors (non computer/efi motors) they can often benifit from adjusting fuel mixtures and timing from the standard settings when the compression is raised . so i would suggest doing a compression test to see how much it differs from standard and go from there . but it seems your deffinetely on the right track. if the compression is raised to much you may need to use a higher spec fuel to prevent pinging. Eg; ron-95/98 instead of ron91 .

just in case it was not clear . i think you possibly have higher compression than when the engine was new and certianly more than before you reconditioned the head .

Quote:

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Originally Posted by nipagu7

if blowby is reduced after reconditioning the head , i think it would most likely been worn valve guides and valve guide seals that was the culprit and possibly even a leak thru the head gasket to a oil gally (which would normally be self evident when you removed the head). with excessive blowby , this means that effectively power is leaking out of the compression chamber and into the oil chamber and out thru the blowby hose instead of being used to push the piston down to turn the crank shaft ' Ie; reduceing efficiancy if there is little blowby now it would suggest the rings are in good condition. i'm not sure what you mean by "excessive machining" but would take it that the head was machined because it was either slightly warped or slightly damaged. machining it will ensure it will seal better when it is refitted to the block. depending on how much it is machined, it can increase compression to the point the engine will noticeably perform better. t don't now much about rb30's but with carburetted and timed motors (non computer/efi motors) they can often benifit from adjusting fuel mixtures and timing from the standard settings when the compression is raised . so i would suggest doing a compression test to see how much it differs from standard and go from there . but it seems your deffinetely on the right track. if the compression is raised to much you may need to use a higher spec fuel to prevent pinging. Eg; ron-95/98 instead of ron91 .

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What happened was back in 2012 when I did the cylinder head reconditioning the head guy had it rebuilt to fix the badly corroded water galleries. I didn't know much about the need to do my own homework regarding the head thickness, so I put my faith in the head guy. The same head five years later(this year) started giving me trouble I decided to do the whole thing DIY. I had a cylinder head given to me by a guy who blew the bottom end of his turbo Skyline RB30. I did the basic measurements of that head and it was good. No warpage, minimum corrosion and thickness was good(RB30 minimum head thickness specs). So, I rebuilt that head in my garage, including pressure testing(my own gear), machining(my own simple gear of sanding table) and valve seats. Then I pulled the old head out of the engine and measured it. Flatness was still good. No corrosion(not much of it) on around the cylinder head water galleries. Then I measured the thickness which gave me a heart attack. It was machined way beyond RB30 recommended maximum machining limit, 1mm to be exact. That would've put cam timing way out, to 'remedy' the bad cam timing issue with ignition timing and the choice of fuel I reckon. So, it would've been running poorly for years. The vehicle is dual fuel & carby. I ran mostly on LPG, so that would've helped with the timing issue a bit 'cos LPG being high octane like 98RON. I posted the details about the "excessive machining" in my other thread. Basically, the head guy machined it way beyond recommended maximum without doing any measurements of sort, effectively boosting the compression to an unhealthy level for a 300k+ bottom end & not to mention throwing the cam timing out as well.

Yeah, I need to do a compression test now with the "new" cylinder head. But, blow-by is obviously not there or either reduced to a level that is not annoying the crap out of me anymore.

As for valve guides, yeah that is possible, except the other signs of valve guide wear wasn't there. For example the idling smoke wasn't there except the condensation smoke on idling when cold started. But, it is possible the valve guides were still bad and contributing towards the excess blow-by 'cos back in 2012 I didn't replace valve guides(I did it this time of course). So, the old valve guides would've contributed somewhat towards excessive blow-by.

I've been told, in RB30 engines, pinging or preignition can happen without producing the characteristic noise in milder cases.

Quote:

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Originally Posted by nipagu7

just in case it was not clear . i think you possibly have higher compression than when the engine was new and certianly more than before you reconditioned the head .

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Yes, that would've been the case from 2012 to couple of weeks ago.
I reckon it should've rectified now. I need to do a compression test shortly, but I'm confident it will show up good values. :)

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Originally Posted by nipagu7

just in case it was not clear . i think you possibly have higher compression than when the engine was new and certianly more than before you reconditioned the head .

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The difference of thickness between the old and "new" cylinder head is 1.6mm.
I'm sure you agree that is a fair bit and no way I can getaway without issues with a difference that much.
I think I'm pretty lucky the bottom end is not apparently stuffed from running the "super thin" cylinder head.
What probably saved the bottom end from total disaster was running LPG I reckon.

the blowby with the old head on may have effectively reduced the compression. if it did have high compression this might not nessicairly been a bad thing as the higher compression would help to cause more efficent combustion . the main thing is the bottom end still seems good. i would still do the compression test and go from there . it's along time since i've had to deal with valve timing issues and not sure how you would be able to effectively measure or adjust them. but i do know it pays to to get your fuel mixtures right and ignition timing right in terms of fuel efficiancy, power output and engine life. with dual fuel running mainly lpg, i would tune more fore lpg than petrol, which would give you even better fuel economy when running lpg . and only run higher ron petrol which will run better with a tune that favours lpg . also the longer the petrol is in your fuel tank the more it will deteriorate, so the better petrol you put in / the better condition it will be when you use it.

Quote:

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Originally Posted by nipagu7

the blowby with the old head on may have effectively reduced the compression. if it did have high compression this might not nessicairly been a bad thing as the higher compression would help to cause more efficent combustion . the main thing is the bottom end still seems good. i would still do the compression test and go from there . it's along time since i've had to deal with valve timing issues and not sure how you would be able to effectively measure or adjust them. but i do know it pays to to get your fuel mixtures right and ignition timing right in terms of fuel efficiancy, power output and engine life. with dual fuel running mainly lpg, i would tune more fore lpg than petrol, which would give you even better fuel economy when running lpg . and only run higher ron petrol which will run better with a tune that favours lpg . also the longer the petrol is in your fuel tank the more it will deteriorate, so the better petrol you put in / the better condition it will be when you use it.

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Yeah, I learnt the effect of old petrol the hard way. I bought a bike that hasn't been driven for good few years and with some old petrol in it. It started and ran, but was running like bastard with a noise like pre-ignition knock(pinging). It got better after I started filling with new petrol. I was scratching my head and was getting ready to do all kinda repair/tweak work on the engine, and luckily had to refill the tank before I started dismantling things. :)

RB30 bottom end is pretty solid I think. The guys usually end up with bottom end wear or blowup are usually the ones with turbo converted ones with improper tuning or improper turbo conversions.
I haven't touched the petrol side of it yet. I need to get into tuning the carby.
For dual fuel, I'm planning to get a dual curve ignition unit to address the issue of different ignition time and curves required for each fuel, or I can stick with 98RON, which is closer to LPG in terms of octane rating.
Fair bit of tuning work need to be done on it. I'll get it done soon. :)

Cam timing/valve timing check is a tough ask without having specific instruments like dial indicator, etc
http://www.enginebasics.com/Engine%2...%20Timing.html

or gizmos like below.
https://www.youtube.com/watch?v=gCffg22c50g

I expect no cam timing/valve timing issues now since I fitted a cylinder head with an acceptable head thickness, but I would love to measure it using instruments as above, so I can learn from it. :)
I did grind the valve seats, but I think the effect on valve timing from that is minimal(I believe).

This is a good article that explains the technical side behind cam timing.

http://www.maruhamotors.co.jp/miata/...lvetiming.html