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Timing Skipped Four Teeth. Valve Change Out Only?

Don Dada

By Don Dada,
in Engines & Forced Induction

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Don Dada Mentor

Don Dada

Posted
Posted (edited)

K guys....I'll try to make it as short as possible so here goes...

Car was in accident and after being down for a while decided to give it a go, so turned the engine(rb26) via the crank bolt and everything seemed fine. Tried to start and it constantly fouled plugs.Killed the fuel pump and barely got it goin(didnt really start) and heard tapping in the head so checked cam timing and both intake and exh cams skipped four teeth.

Set back timing as normal and did compression test. 1,2,5,6= 150-160psi, 3= 0psi, 4= 30psi.

So all intake valves kissed the pistons

post-42272-0-01677200-1392601981_thumb.jpg

Valves looked normal tho

Number 4

post-42272-0-32633000-1392601952_thumb.jpg

Number 3

post-42272-0-62684900-1392601924_thumb.jpg

Piston after cleaning the carbon off

post-42272-0-91316800-1392601894_thumb.jpg

post-42272-0-47717900-1392601852_thumb.jpg

The pistons dont look bad at all. From what i see it basically just smoothed out the rough finish on the piston top from the hit, but nothing I think a little rub with a piece of emery wouldnt fix.

Soooo....Im thinking the loss of compression is due to bent intake valves on number 3 and 4 even tho all of them look the same as the other cylinders???

My question is.....Can I get away with changing just the intake valves without touching anything else?

If so,I think I would change out all even though 1,2,5,6 read good compression.... and this leads me to another question.....How come only 3 and 4 lost compression? Shouldnt all the intake valves hit the piston to the same degree and cause the same damage across the board? as I did crank the engine like 20 times trying to get it to start!

What do you guys think

Edited by Don Dada
Blackkers Experienced

Blackkers

Posted
Posted

that is a weird result... before you pull the valves out I'd be doing the kerosene trick where you let it leak overnight to see which valves are actually sealing properly.

Also what kind of accident was it that caused the timing belt to jump 4 teeth on the crank pulley? sounds a bit strange

Shoota_77 Veteran

Shoota_77

Posted
Posted

Was comp definitely good before the crash? May have busted ring lands or something that is hard to see.

Make sure the valves aren't sticking in the head and just being pushed closed by the pistons. It only takes a tiny nudge to bend valves which can cause them to lock in the guides. With the head resting on timber so you don't further damage the valves, turn the cams around and see if the valves close of their own accord when the bucket comes off the lobe.

Don Dada Mentor

Don Dada

Posted
  • Author
Posted

Yea...Engine was perfectly healthy before. When I look off the head I was able to spin the intake cam by hand and watch the valves open and close. It was a little hard to turn in some spots but I guess thats normal depending on the position of the lobes against the buckets.

Will see if I get some time to do the kerosene test for now and I guess that would confirm leaky valves on 3&4....and if so then removal and inspection of the guides

r33_racer Grand Master

r33_racer

Posted
Posted

More like replacing valve guides, stem seals, new valves most likely unless their run out is not bad, then seats will need to be cut.

However if you pull the valves out and spin them in a lathe or drill press or even a hand drill and if somehow they aren't bent, you might get away with just a heavy lap in to make sure they are sealing and then all good.

  • 2 weeks later...
Don Dada Mentor

Don Dada

Posted
  • Author
Posted

Well got some time to scrap out the intake cam and manifold and pour kerosene in the ports and well it instantly emptied out no. 3&4 and it also leaked out all of the other cylinders but at varying rates, some just barely seeped through.

Is it supposed to seal 100% so that absolutely no kerosene should pass through? Remember 1,2,5,6 read basically perfect compression.

r33_racer Grand Master

r33_racer

Posted
Posted

Valve seal should be 100% when a head is brand new or reconditioned. In your case if they leak a little that's probably not too bad. If its leaking a lot then recondition time it is.

Hopefully 3 and 4 might need abit of machine work, but the others might just need a lap in with some fine paste and they will seal back up.

GTRPSI Mentor

GTRPSI

Posted
Posted

If you have the steel valve guides, take a close look at the tips entering the ports in case they are cracked after you remove the valves.

Looks not so bad on the piston front, id say 4 new intake valves, a bit of a lapping in and it may be good to go.

While your in that state, i may be wiser to just replace the 4 intake valves and get all the seats recut, valves resurfaced and lapped to ensure max compression.

Your there now, its not mega $.....

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