Just too be clear this questain is not related too wood gas in any way, i am just a novice engine builder looking for ideas too produce a more sure product.
Are there any tools afordable too measure the smooth ness a of a crank shaft after turning the crank,A good cast crank shaft machine shop should be polishing the crank after turning too get the proper finish, it would be nice too have a scope of some kind too check the finish before a rebuild.??
1 Like
I gess my last questain was just too dumb too answere.what i am looking for is are there any electronic microscopes that would work too check crankshaft surface finish after machining.and i dont really know what ra 6 or ra 8 finish is.as this is the finish on like a jasper crank after they hookup there new crank shaft polisher type.Some sort of tape polishing machine that is equal too 600 grit emery cloth but is much more consistant, not relying on how hard or long the opetator could time out.
Hi Kevin,
Firstly, no questions are stupid, they are only inquiries. I have rebuilt 3 or 4 VW engines and had a machine shop do the crankshafts. Pick them up, take them home, they are ready to go. Their equipment centers them perfectly.There is no final smoothing that they do. The bushings (oversized to match the crankshaft grind) just slip in place and you are ready to go. Doing any thing by hand on the crankshaft will not reestablish the center of rotation, but only exaggerate the off center or wear pattern and probably increase the slop for a premature failure. Not recommended in any instance. This is the heart of the engine and requires expert handling and is well worth the cost. I did install a VW crankshaft and couldn’t turn the engine over by hand. Scratch my head. The VW guy whose shop I was using told me to take it apart and he’d show me my error. Improperly installed the bushings and ended up with visible flat spot on the insides of the bushings. The crankshaft being much harder showed no damage. He told me to try 600 grit emery cloth to take out the flats on the inserts. Hours later I reassembled the parts and it was free wheeling. Drove it for 100,000 miles after that with nary a knock. Hope this helps.
Pepe
2 Likes
Thanks for reply the Richard pepe, i have too admit i have hand polished a crank or two and not many success storys too brag on there, and i have put low compression pistons in the wrong block only too here a loud poping noise after starting. I have had nice turned cranks grind up a new set of bearings in few weeks,so i went on line checking crank shaft tech sites and i gess a better crank grind shop polishes each though a few seconds too take off the ferret burrs left behind from the carbin that is in the cast iron mix. If i could remember how too post the web link i would.I supose i could call more crank shaft shops and see what they use too check there machine finish,There may be some fly by nite crank machine owners.And the motor block can be a hard componet too get clean after a bearing fail, so i usually pull all the oil gallery plugs too rod them out while rinseing out all oil gallerys.I will not put another motor together with out at leaste plastigauge. As i have most all other rebuilds before. Even that is not a very acuret way too measure for the 1 too 3 thousans clearence needed for various motor specs. Some of the newer motors run tight as 1 too 1-1/2 thousans clearence. And require 5w20 or thin oil compared too the old 454 chevy race motors run over 3 thousans clearence and use 50 weight oil required.Any way maybe some engine techs will chime in with thoughts on the subject. Thanks.
3 Likes
By the way, remember there are two very different Ra measurements. In the US, we tend to think of Ra in micro-inches. My associates in Australia refer to Ra in micro-meters. Therefore, a 6 Ra in the US is a super fine polish, stated as .15 Ra in Oz. 6Ra in micro-meters is something like 250 Ra in micro-inches.
As for measuring surface profile, I use a “profilometer” though that’s actually a brand name of stylus type measuring device.for surface smoothness.
2 Likes
Thanks for the ra measurement definishen , i think that was the polish serface of a jasper engine crank after they installed there new polishing machine,or are in process of installing it.
1 Like
Engine ready too install, plasti gauge shows about 1.5 thousans oil clearance, see how my oil psi reads when hot.turned the crank 10/10 , the regrind looks ruff compared too the cam.??
2 Likes
Hi Kevin,
I’m not a machinist, but I’ve replaced a number of crank and cam shafts on rebuilds. I’d say if you can see “ruff”, then you should reject the piece on a quality assurance basis. Look what you stand to lose from a cranky crank. Hope it doesn’t get rough on you.
Pepe
1 Like
Thanks pete me too, the crank wasent really ruff, i was thinking why are they never as smoth and shinny as the cam sirface. I honed the bores,hopefully the rings will seal with out burning oil, the bore dident have much rig though i dident check the piston clearence, out of money out of time. Hope fully wood gas will help seat the rings, they say not too choke or flood the motor while seating rings.And i need the weight in the truck for winter ride sleding.
2 Likes
Well chevy cam bearing engineers are nuts. They had too make every cam bearing diferant in one measure or the other.The size of the block bores are all differnt.dont be fould by the simplicity of nock out old ones and slam in the new bearings. Every bearing is a differant measure in one aspect of the other fit. The box of bearings look simple. 26 one 27 b is 2 28 3 and 28. 4 and 27 5 is the other end. With 2 oil holes on the one end bearing.Th problem is mainly 28 3 and 28 4. As both bearings are stamped B 28 and if you cross them from moveing them around, you will have something like 6 or 12 000 off on the clearences.So i must pull my motor too replace the faulty bearings to prevent preamature engine failure. And those lousy bearing outfits may not mark the bearings properly as in my case from engine tech.And as i leared know the hard way the press fit should be about 3 thousands bearing pressed intoo the block casting or if not than likely need too use the other 3rd or forth bearing too fix the proper press fit clearence.What a joke on behalf of one of chevys lousy ideas.line bored cam bores are all one size no bs select.
1 Like
Got my cam Bearing press out and install tool for 35.00 too the door from karl performane on ebay. Works on small block chevys 1955 too 1999.
<img src="/uploads/default/original/3X/9/3/931410c857ba42847461a68f2c0d21
I am more confuzed and more enlightened. It looks like the cam bearing id seem to be the same though the od is quite different.so why wood the block bores for the cam bearings be diderent sizes on the old chevy v8 motors i dont have the foggyest idea.???$$$
Correction on the markings the two b_ 27 bearings are the same as close as my dial calupers can read. And the two b-28 bearings are same size bearings on my new set of cam bearings. The first set i installed had next too no markings and i should have requested a set of bearings with more proper stamp markings not just markings on the box locations.Rush Rush Rush, get that 5 star feed back.sent out wrong marked cam bearing.