theoUK

Anyone good with vacuum diagnosis? Am i just worrying about nothing?
Tested the manifold vacuum the other day - at idle the guage needle jumped around like hell. It bounces quickly ("too fast to see" quickly) around the 15 inches mark, but the oscillation is like +/- 10 inches. As you increase the speed, the bounce begins to flatten out, and it approaches a more steady reading.
Is this just a characteristic of a lumpy cam? I have a crane fireball 290 in there. Don't have the full specs to hand.
The only reason i worry is that the guage manual said a wildly oscillating needle suggests a broken or weak valve spring, which naturally i could do without.
I guess if i had a broken spring, i would have heard it? Never had any experience of this - what do they sound like? Also the guage manual is obviously pitched at stock motors. So am i just being paronoid?

Skeets

yes. :D

SAC

I think I would try a different vacuum guage. Mine bounces around about +/- 1.

BB2B

I am not totally familiar with your cam but I would expect to see a lot of bounce with a more radical cam. The bounce in your case is likely reflecting the valve overlap ground into the profile. If you had a broken spring the miss or backfire at rpm above idle would be noticable.

UKPaul

Measuring my manifold vacuum gave a small amount of needle "bounce", but nothing like you've described. Have you tried measuring the compression on each pot?
I know that cams with large overlap cause low vacuum at idle, but don't know how that would show up on a sensitive gauge :confused: Could you post up anything you find?
:cheers:

theoUK

I'll be doing a comp test tomorrow, so we'll see what that brings up. Not too much hopefully.
Incidentally, for anyone who has recently done a vacuum test with a similar cam to mine, the specs i have for it are

intake opens - 35 btdc closes - 75 abdc = advertised duration 290 deg

exhaust opens - 75 bbdc closes - 35 atdc = adv dur 290 deg
The spec sheet gives the lift (at valve, with 1.5: 1 rockers) as .454" exhaust and inlet.
So the question is, would that spec just cause a low steady vacuum, or the madly bouncing needle like i've seen

As a matter of fact, I read today that if the needle fluctuates at idle then steadies out at higher speeds, (like mine) it points towards worn valve guides. This could well be the case, as i've suspected this for a while - from the classic "puff of smoke at startup after a long rest, but no major oil consumption" symptoms.


:confused: :confused:

theoUK

OK, did a compression test this weekend. Thankfully that looked good. Bit of a pig of a job getting to all the plugs. My manual gives 150 psi as the "target", with no more than 20 psi cyl to cyl variation. I'm gettting 140 to 145 psi on all pots, and this is coming after no more than 2-3 strokes in each case. So didn't bother doing a "wet" test after that good result.

In the absence of anyone's advice to the contrary, I'm putting my bouncing vacuum gauge symptom down to worn valve guides - can anyone confirm that?
:confused:

Dalannex

Sounds like you probably do have a little wear on the vavle guides, I would chalk it up to that and enjoy the cruising season. :steering:

-Justin

UKPaul

Nice compression readings :yesnod:
I'd try measuring it with a different gauge before writing off the guides. I had strange readings with a dwell meter once (Hi Justin, remember that little episode? :D ) & another meter worked fine.
Could you have a leak at the carb base, vacuum lines, manifold gaskets? A simple check on stem/guide wear is to pull the covers off & then grab the spring cap of each valve & rock it. Any excessively worn ones will be easy to detect.
:cheers:

theoUK

Justin, I'm inclined to agree about just getting on with enjoying summer - it's gonna be a scorcher this week, trouble is my vette's in pieces in the garage, while i sort out a timing cover oil leak and wait to get hold of a harmonic balancer puller. :rolleyes: Back on the road next w/e though, when it will start to rain :lol: Still, although it's nice to "know" what's wrong with the motor, it's not like it's about to blow up, so I'll not get too worried until i can afford to have the heads off for a proper job.

Paul - yeah, I was pretty pleased with those comp test results, if nothing else, just for the consistency between cyls. Seemed very little point in doing them again wet, to see what the rings are like. So not all news is bad with my car at the moment! I'm having a bit of an oil leak-fest at the moment, so the rocker covers will be off, for new gaskets, very soon. Perfect time to have a look at the valves. I wonder how much they'll show up the wear with the tension of the spring still attached? I suppose if they're that buggered, they might give a bit of wobble. I'm not saying they won't - just never tried that test with the spring still on - perhaps you know something I don't? :)

Also, might be a bit messy, but I was thinking of testing the vacuum while i squirt a little oil directly through the springs, onto the stems. If the guage settles, I've got my culprit!
I'll keep you posted.
:cheers:

UKPaul

Theo,
Wobbling the valves when fitted can give a good indication of wear. I discovered this years ago on another pushrod operated engine. Wobbling it in line with the rocker arm shows up the wear & side to side (ie forwards & backwards in relation to the engine) should give none/very little. I compare the two amounts of movement to get a very approximate guide as to how much wear there is (this won't apply to engines that have had a major problem (ie lack of oil) as the guide/stem will have high wear all round). What I found was that most wear was caused by the rocking motion induced by the rocker arm if the pushrods were the wrong length eg head/deck skimed, different base circle on cam, etc & no checks made on pushrod lengths. I tried it on mine without the springs fitted & then tried it with them fitted & the results were consistant ie the guides with a bit more wear also showed up with the springs fitted. The springs just keep the valve closed, they don't really stop it from being moved side to side. Just use finger pressure to check it. It's hard to describe but after you've done it you'll see what I mean. You probably won't be able to pick up slight wear, but excessive wear (what you're interested in) will be obvious. In fact, the more wear there is then the easier it will be to wobble it.
Do you know what type of valve guide seals you've got fitted?
Good luck with the oil leaks. I used those rubber valve cover seals & some silicon RTV which works well.
:cheers:

theoUK

Paul,
That's interesting... I guess my first thought was that the tension in the spring would stop things from moving, since in order for the valve to wobble, the retainer would have to wobble with it, and this would be largely prevented by the spring. If you see what i mean!:lol: But I guess not - if things are really worn, then it would be all the more obvious.
Not sure what valve guide seals are fitted, I haven't been in there since i bought it a year ago. I'm concentrating on bottom end leaks at the moment. I've been lazy and left a front seal leak for too long really, just 'cos i knew the car would have to be off the road for a few days. Trouble is, it's got to the point now where oil slings off the balancer and blows back, when the speed permits, onto the downpipe. Smells nice, as you can imagine. It's all a bit wet down there. I read a post on another forum today about the troubles of getting that front crank seal to do its job. I'm hoping it hasn't worn a groove in the balancer shaft - seems that this is the reason that a) it starts leaking and b) it carries on doing so, even after a new seal goes on. Hopefully won't have to get the shaft built up and refaced, although my work could do it for me, it'd be a right pain in the ****!

UKPaul

Theo,
Nothing quite like the smell of oil on hot exhausts!
If the balancer shaft is worn (it's amazing how much wear a lipped seal can cause on a hardened steel shaft) it might be worth giving Corvette Kingdom a call. Ray keeps a lot of used stuff & his prices aren't bad. Not sure what a new one would cost.
It's been over a year since I had mine off, so I can't really remember what it all looked like. But it might be possible to turn a small amount off the end of the shaft so that the damper moves closer towards the timing cover. Then a new seal would be running on virgin shaft. The pulley could then be placed in the correct position with shims. Would that work? Just a thought.....
Where are you getting a puller from?
:cheers:

theoUK

I've dealt with Ray before, and found him to be a good bloke - I picked up a used cruise transducer and some other odds and ends recently. I think i'll go for keeping my old balancer if possible, I hope a bit of machining should see it right. There is some extra land on the balancer's shaft, so taking a bit off the end could work out to be a really good idea - hadn't thought of that yet, nice one! :D
My first idea was to measure the unworn shaft, then turn it down and sleeve it back to the right dimensions. We'll see what the best plan is when the thing's on a bench in front of me....
I'm actually not sure where i'm getting a puller from :D - sounds a bit dim, but it's true. I've asked a few of my work mates, and most have just got a standard hub puller which, of course, is no good. There's one more guy i'm banking on, and will ask him today. If not, then i could well be making one up. Seems strange that and university engines research group doesn't have a harmonic balancer puller - i used to work in a humble little country garage, and we had more than one. :confused:

UKPaul

Theo,
If you get stuck I've got a puller/installer you can borrow. It's heavy so postage could cost a bit (I ordered it from Summit & it came via air. The freight cost was frightening & then there was duty & VAT stuck on top of the total. So the postage costs, including tax on postage costs, was more than the actual tool! :cry ). Let me know if you need it.
:cheers:

theoUK

Paul,
Thanks very much mate, kind of you to offer. I'm hoping it won't have to come to that just yet, although I really appreciate the thought! :cheers:
I've not exhausted all my possible avenues yet, there's a few more people i have to ask today. I work with about 25 research engineers and about as many technicians, and as yet haven't found anyone with anything more than a regular hub/bearing puller - bloody academics, they're just not practical enough!
If all else fails, I'll get in the workshop and make one up - in fact the guys here would probably do it for me at the drop of a hat. I've got one chap making me a stainless dipstick tube ( he feels guilty 'cos he tack welded a mounting bracket on to my old one and blew a hole through it :lol: ) I'll not let him forget that for a long while.....

And i feel your pain about international postage. I bought about 30 quids worth of really light stuff from Ecklers the other month (plastic interior trim etc, less than a kilo) and got stung nearly as much in postage for it. It looks so cheap in the catalogues.........

theoUK

By the way, you say yours is a puller/installer....
Do you need an installer? Will the pulley nut not just draw the balancer back on, if you have the flywheel ring gear locked?

UKPaul

Yup, had to work with a few myself (I think I'm meant to be one :lol: ). I remember getting really wound up once while 3 of them took an entire week discussing the best way to put a shelf up! They were almost at an atomic level, analysing the elastic properties & shear strengths of various rawl plugs, were the best screw to get the galvanised ones, or plain steel..... Come the weekend the shelf was fixed to the wall (I expect he spent ages measuring for the holes, calculating the wattage of the drill & the additional cost on his electricity bill!) & then (& this is no :bs ) it fell down when stuff was put on it. They hadn't allowed for anything but the weight of the shelf :lol:
I did. The balancer was so tight on the crank nose that it'd probably damage something trying to pull it on with the bolt. I guess it depends how tight yours is, but mine was so tight that I stopped twice & took the tool off just to check that I was doing it correctly ie. I was putting a LOT of torque on it, but the balancer wasn't moving at all - it felt like I had set the tool up wrong & was trying to rip the crank out of the front of the block!
Keep that guy feeling guilty about your dipstick tube (original part, rare as Hen's teeth, value of car is reduced, etc) & get some more stainless parts made! I love stainless, especially when it's mirror polished :D
:cheers:

theoUK

Yeah, I'm supposed to be one too! In fact, i'm the first to admit I can get too stressed out about the finer points.
I like the shelf story, sounds like a bar-room joke! There is a story that says the new library at my university is sinking into the lake (it's built in the middle of it, bridge going across, very nice) because the civil engineers forgot to design for the weight of the books. I so hope it's true, but suspect it could be bollox. Nevertheless, it kind of sums up the moral of your story.

One of our guys is going to have a look for a puller on the weekend - he has a famously vast arsenal of tools, so i'm hoping he'll come up with the goods. I'm a bit apprehensive about the "putting back on" process. How does yours anchor on, to push the balancer back on? Does it screw down into the pulley hole, or what? Maybe my workmate's is the same as yours - i imagine they are fairly generic. I know what one looks like, but can't picture how its used to actually re-install the damper, other than screwing into the pulley bolt hole....

The dipstick tube saga is a blessing in disguise - the old one is bent to buggery and a right pig to push the dipstick into. A smoothly curved, polished stainless one will look cool. Then i'm thinking sandblast the handle and paint it. I've just finished painting various bits of bracket and godknowswhat. I had it all out to get to the front cover, so spent a couple of hours sandblasting yesterday, and put some lo-gloss black on all the bits. Can't afford to chrome them, so it's a happy medium since it looks tidy, but doesn't draw too much attention to the general mess of brackets. Hoping to ceramic coat the headers before they go back on.... Money money money :rolleyes:


[Modified by theoUK, 1:39 PM 8/5/2003]

UKPaul

Theo,
My memory isn't very good, so (if I remember!) I'll take a look at the tool tonight. What I do remember is that a hardenend stud is screwed into the snout of the crank & the tool is tightened up on that to pull the damper on? If the pulley bolt is used then it could strip & cause damage. An engineer once told me that a bolt/stud/nut has to be engaged for 3 turns of thread for the maximum strength to be obtained (could you verify that with any of your guys?) so if the pulley bolt is used & only 1 thread is engaged when resistance is high then there's a good chance of it stripping.
The above is mainly guesswork based on a bad short term memory :) I'll get back to you tomorrow after I've had a look at the tool. If I remember :crazy:
:cheers: