3TG valve problem - help/advice needed

[jb_22]

Hmmm... So I reshimmed my cams on the 3TG last weekend.

The weekend before I measured the valve clearances, pulled out the cams & measured the shims to order new ones through Precision shims. All went together okay with the new shims and I measured the valve clearance - all okay, little tighter than I estimated but nothing unusual...

Started her up and within a couple seconds there was a rattle in the top end, so took of the cam cover & checked the clearance again after less than a minute of running the motor. #2 exhaust clearance before starting the motor was 0.28mm, now it is out to 0.55mm... hmmm... compression test and there is absolutely no compression on #2 cyl - needle doesn't even move. Wondering how I bent the exhaust valve??

When I was measuring the valve clearance on the exhaust cam with the new shims, the intake cam was positioned with the notch just slightly forward of where it is at TDC to ensure the inlet & exhaust valves don't hit each other, and vice versa when measuring the intake cam - only with the notch in the exhaust cam slightly backward. The bottom end was ~30 degrees BTDC, but #2 piston would have been near the bottom of the bore so it can't have hit the piston. When turning the cams over by hand with a spanner on the hex shaft there was never any point that felt like interference either.

The cams were dialed in correctly - motor at TDC, the cam notches inline with the arrow on the cam bearing cap, timing chain tensioned, sprocket pins installed, cam bolts torqued & the motor turned over by hand to check it after a couple revs.

SO yeah, what you guys reckon caused the valve to bend?? Could it be something else?? i.e. it's a bit of crud on the seat that's stopping the valve sealing? Pretty devo cuz a bent valve means the head's gotta come off for a reco... Grrrr.. Probably use it as an excuse to go larger valves though.

Any help/advice is much appreciated before I jump in the deep end and take the head off

Cheers, Jess

[Celica RA45]

when doing shims, its easier to take both cams out drop all cylinders down to bdc or even across the block , then do exhaust
1st take all measurements plus or minus .

then take out ,do the same with inlet etc and always torque up cam caps as well
also another thing ,,inlet is normaly 9 to 13 thou .i set inlet up to 13 thou
on exhaust 11 to 15 do the same set to 15, as over time the shim clearence does close up

ok on your problem you would have hit valves together , quite easy as inlet gets very close to exhaust

[jb_22]

Even with the cams in the position I described? That's where the Brooklands OWM manual I have says to position them to make sure the valves don't hit. I would have felt the cams interfere when turning them over if that weren't the case?

Also, I rechecked the shims after timing the cams in & the clearance was good on #2 exhaust when turning the motor over by hand at least a half dozen times. If I bent a valve while shimming the cams surely I would have picked it up while rechecking the clearance with the cams dialed in? Only after I first started it then noticed the rattle then rechecked was the clearance out.

Cheap way out is I get a single replacement valve and lap it in with valve grinding paste & reuse the HG (done ~2000km).. Anybody gotten away with this before?

[J-M kujala]

taking one cam off , usually they rotate a little and hit to each other, or to piston/s... there is many way to do this, but always had to be so F*cking carefull... and keep the Cam / Cams in correct position somehow, or in position where they dont hit. i do not assemble or re-asseble engine in TDCC, just turn off pistons at tdcc and do work, when assebling, first cams to correct position, then turn the crank to a correct position. but that have be near, not far maybe like 30 degrees.

take timing chain off in "timing position" inlet or exhaust cam try to turn and hit to each other or pistons, they had to keep in place... if doing it in that position.

i have buy a lot 2TG engines where valves are bendt... and someone loose inspiration or burn nervous XD

everyone learn it in hard way...

[w810sc]

The only times I can see the exhaust valve being bent:

- during the exhaust stroke,
valve open for too long and piston makes contact with valve,
valve relief not deep enough and piston makes contact with valve,
valve relief different angle.

- TDC, end of the exhaust stroke and beginning of the intake stroke,
the overlap where both intake and exhaust valves are open, too much overlap and both valves hit.

what cams are you using?
how much lift do they have?
did you degree them?

I know it sucks man, I've been there. Best thing to do is remove the head and go from there.

[71TA22]

Just asking an obvious question but was the valve already bent when you re-shimmed?

Take the head off and rebuild on a bench. Support head so valves dont touch bench when turning cams - or you will bend more of them.

[jb_22]

The only times I can see the exhaust valve being bent:

- during the exhaust stroke,
valve open for too long and piston makes contact with valve,
valve relief not deep enough and piston makes contact with valve,
valve relief different angle.

- TDC, end of the exhaust stroke and beginning of the intake stroke,
the overlap where both intake and exhaust valves are open, too much overlap and both valves hit.

what cams are you using?
how much lift do they have?
did you degree them?

I know it sucks man, I've been there. Best thing to do is remove the head and go from there.

Yeap head's gotta come off - no two ways about that.

I've got the 88222 cams with ~10.3mm lift. I'm also using 3T pistons with exhaust valves milled bigger to suit the higher lift cams. When you ask if I degreed them, they are stock cams AFAIK & the procedure I followed was to align the notch on each cam to the arrow on the first bearing cap while the motor is at TDC, installed sprockets with sprocket bolts finger tight, retension the upper chain, check motor is still at TDC, installed the cam dowels into whichever hole lined up with the sprocket holes (with rags stuffed down the front of the head to save that little dowel from falling to the sump if I dropped it), then I torqued up the sprocket bolts & turned the motor over a couple times to check the cams are still aligned.


71TA22, I doubt the valve was bent before reshimming- #2 cyl had compression before I reshimmed and the valve clearance was ~0.40mm. Shim size was ~2.20mm, went to a 2.30mm shim & the new clearance was 0.28mm when I reinstalled the cam, all goood. Then I started her up after putting everything back together, noticed a top end rattle, killed the motor & when I rechecked the valve clearance #2 ex was 0.55mm. Did a compression test to check if the valve was bent as low-and-behond zero comp...

I did the exhaust cam first with the inlet cam out of the motor. Before I installed the inlet cam I positioned the exhaust cam with the notch just on the inside of the arrow on the bearing cap (where the cam naturally wants to sit when you lay it in place) This is how my Brooklands OWM says to position the cam so the valves don't interfere when checking valve clearance. In this position the #2 exhaust valve (the one that's bent) is just opening for the exhaust stroke, so I guess if they were to interfere then #2 ex would be the one to get bent :\ It just sucks that I was uber carfeful with positioning the cams and I still managed to bend a valve. Meh, you always learn these things the hard way...

& yes that advice is important! Last time the head was off I used a piece of 12mm pine wood at the back of the head and the two studs that bolt the front timing cover when I did the valve stem seals on my workbench..

Soo the debate is on... Is it worth going to OS valves and have the car off the road for a month or so while I source valves & get headwork done? OR counter argument get a single replacement OEM valve, lap it in & be done with it for a weekend worth of work...

[J-M kujala]

3T "stock" pistons need a lot work with valve pockets when used on twincam heads, wider and deeper to run without contact.

That drops CR down to ~ 8.5:1

Have you modify youre pistons enough?

Wiseco 3T pistons got big enough valve pockets.

[jb_22]

I had a set of 8.8:1 CR 2TG pistons (2TGR) to measure the valve reliefs, the 3T pistons needed only the exhaust valves milled. This is what they looked like before:


And after:


The exhaust valve relief is bigger than the 2TG pistons. The machinist measured the angle and distance to the relief on the top of the 2TG piston, and cut the reliefs on the 3T pistons the same, but didn't take into account the lower dome height - hence bigger reliefs.

Yes it drops the comp ratio, but the 2TG head is slightly smaller volume than 3T so that bumps it up again. I would have really like some high comp 3T pistons but couldn't afford them at the time.

[J-M kujala]

to my eyes exhaust pocket are big enough, maybe radius is a little to big but they should work. timing maybe have been incorrect, i think you will found places where it hit.

have check that valve end is not to deep in the retainer ? that wont bendt the valve but make moving lash.. so the adjusting shim press end of the valve, not only retainer a little and then a valve..

if you found bended valve, check valve guide also, they sometimes crack when valve bendt (if there is oem style iron guides)

[jb_22]

The shim sits above the height of the retainer if that's what you mean? the lifter has an embossing in the centre for the shim so the lifter won't hit the retainer. But that problem would mean the valve is still sealing & I would have comp on that cyl. At the moment the compression tester needle doesn't even move when cranking it over - says bent valve to me.

I will check the valve guide too, if it's shagged I'll probs be saving up for a head reco with all new valves and guides. Stewart Wilkins have a pretty good price for "competition" valves & bronze guides. Might have to give 'em a call and find out what size the valves are.

[J-M kujala]

mine SW valves was same than SI Valves (From US) ... intake or exhaust valve grooves was not deep enough, they had to modify . but that was like 4 years a go. they are a little bigger. (RG size)

Sleeka spares got oversize japan made Dokuro valves, i think they are near OEM quality, looks a really good and material feels like oem... but a little bigger also.

[jb_22]

Are you talking about the grooves at the top of the stem to seat the collets (what holds the retainer in place incase?

Sleeka Spares sounds like the go, I've dealt with David before and he's pretty switched on with Toyota stuff, and he often gives a discount for buying multiple parts

That's if I replace them all, if the guide is okay then I'll just replace the one valve with OEM to save some effort & money. That way I can do it at home and won't have to take the head to a workshop for machining.

[J-M kujala]

Yeap valve lock grooves what lock up the retainer in place, they had to machines deeper,

I dont know if they are correct now, or SW Modify them in Aus. But just want to tell that this had to check. Its basicly 5minit job to machine shop to fix this.

[71TA22]

jb-22,

Have a good hard look at the valve guide. I have had the factory ones cracked but you cant see the cracks when they are cold. Heat them up in oil and the cracks show up.

Have you checked the shim/lifter/upper spring seat on the no compression cylinder? If a shim shifts out of the upper spring seat pocket it vastly increases the chances of piston or valve interference. You will see a bright mark inside the lifter and probably on the shim itself if this has happened.

Is the lifter itself the correct diameter for its sleeve? These can rock in the sleeve if the diameter is to small increasing chances of the shim moving.