Has anyone documented the balancing process re. pistons,rods, etc.?

JonT · 11-10-2015, 07:58 AM

Thanks just looking for specific information regarding this process. Question: my pistons are still in their respective cylinders (this is how the mechanic took apart my engine and I rec'd it from him), should I remove them for balancing or will I create more problems doing this?

tocobill · 11-10-2015, 08:01 AM

Stamp the cylinders if not done and you can scribe the inside of the piston with the respective cylinder. IF moved to a different spot this can be removed to avoid confusion later.

Best is to ask your guy what he wants if he is going to get the parts back to rebuild.

JonT · 11-10-2015, 08:06 AM

I'm doing the rebuilding since it failed the first time he rebuilt it and couldn't identify the problem so I'm not paying him to fk it up again. I was just planning on using a permanent marker to label each part for identification.

tocobill · 11-10-2015, 08:09 AM

yeah that works too ... just be careful not to wipe it off. been there done that. Royal PITA.

JonT · 11-10-2015, 08:20 AM

lol I could see myself doing that! do you think Im ok removing the pistons from the cyliders or should I leave them? Im worried about the rings and how they are seated now and if that could screw things up. I suppose as long as I keep each piston with their current cylinder I'd be ok? no?

Spenny_b · Spenny_b's Garage

My 2p....if you're rebuilding an engine that hasn't gone too well thus far, you'll be wanting to go the whole hog and measure everything....bores (in X&Y) at the positions that are described in the various reference docs...you'll also want to measure your pistons.

If it were me, I'd be throwing a healthy amount of cynicism at it, and make the assumption that it wasn't put together with a thought-out plan of component weight matching (or even the correct pistons back into the correct bores, as they were taken apart..)

Inspect, inspect inspect....now is the perfect opportunity, unless you have good reason not to...

Just my humble...

tocobill · 11-10-2015, 08:33 AM

Eventually youll need to remove them. I would wait until you need to do that. Alot of guys get over excited and jump the gun ripping stuff apart. Later they forget what or where stuff belongs. When you removed them make a paper pocket out of some loose leaf paper. This will protect the ring and easily label them. Another point is if you are swapping the pistons that youll want to keep the sets together. Also rings are cheap so when in doubt ... start over. Have the cylinders measured for heights. They should be stamped for groupings but in the end when your machinists measures the rods for center to center lengths and weights its just one more thing for your blueprints. Your local machine shop should be good for questions or bouncing ideas off of. My local shop never had any issues with me picking their brains for knowledge. Buy and case of beer and drop by the shop. Youll prob get the best and cheapest advice ever ... plus a face/name for later.

JonT · 11-10-2015, 10:19 AM

Spenny_b- agree with you on measuring everything and healthy cynicism towards my rebuild. That's why up to this point Ive purchased a new (used std/std) crank and had Armundo at CCR do his magic on it (cross drilled, magnefluxed, new plugs, polished) and he also sized it for .0027-0028 oil clearances with the rods that were R&R'd by Ted Robinson at German Precision. New Clevite 77 rod bearings. Ted also R&R'd my heads, valves, valve guides, new springs, reground valve seats etc.

Why have the cylinders measured for height?

tocobill · 11-10-2015, 10:25 AM

Height affects CR in that a short cylinder vs tall cylinder. Rod length also comes into play. All these measurements give you your blueprint tolerances. My r&r rods were slightly off center to center when measured. I had one perfect rod that i couldnt use due to the others. My cylinders were also slightly off from the spec height group. I ended up shimming for CR. I had to shuffle all the parts around for balancing and then for my deck height. I wouldnt assume anything on your engine right now. Measure measure measure.

JonT · 11-10-2015, 11:02 AM

These are not new cyliders--they are the same ones that were on the engine. How would the height change? When Ted did the rods he centered the bores. Is this just standard duplication of effort to have them remeasured?

tocobill · 11:17 AM

I guess my feeling on this is the following ... and just my opinion. You had an engine that was rebuild and then failed shortly after rebuild for unknown reason. You got a bunch of parts back and have no measurements or specs on the parts or rebuild .... at least thats what I got out of your orig post in another thread. Have your rods been looked at since the orig rebuild by another builder and spec'd? If so then disregard. If you are going to have everything measured and spec'd then have it all done. Having the cylinders measured saves you from finding out issues later when you are assembling the engine and trying to get a specific deck height. It cost maybe $50 to have all this done and then you have known specs etc. As you know rebuilding these engines is not cheap and not worth rushing.

JonT · 11-10-2015, 11:25 AM

Thanks tocobill I appreciate your thoughts on this. All of the recent work I described above has been done since the first rebuild failed (spun rod bearing). I will get the cylinders measured so agree a baseline for all parts will be established.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by JonT

Thanks just looking for specific information regarding this process. Question: my pistons are still in their respective cylinders (this is how the mechanic took apart my engine and I rec'd it from him), should I remove them for balancing or will I create more problems doing this?

JonT,

Overcome your anxiety and relax. Since you are planning to do weight balancing of the components, you will ultimately disassemble them and check the weight. Use mark pen and zip lock bags to keep these parts sorted and identified. The first step is weighing individual parts or components and keep them labeled. Tabulate your data and you have all the information you need to mix and match a set. The trick is to be able to maintain your focus not to misidentify any component during the process. In spite all this prep, there would be a moment of confusion. As a second control, I placed marker on every parts and placed each in individual zip lock bag.

Use Excel and tabulate the weight. Then you could play around which combination of parts gives the best arrangement over all. Try to use one component at a time. For example, take out from the bag one (1) piston wrist pin at a time. Wrist pin should have some identifying marker on it to match the bag number. This was my technique and was less stressful getting the final setting. HTH.

Tony

fred cook · fred cook's Garage

If your pistons are from a matching weight range, they should be ok. Still, it is easy enough to weigh each one on a home scale that reads in grams. I bought a new set of Mahle pistons for my engine's rebuild and found them to be + or - 1 gram variation. Close enough for a street engine! The rods should be balanced for total weight as well as end for end. That is, all the small ends should weigh the same and all the big ends likewise. Someone with a crank balancing machine will have to check it as both static and dynamic balance will have to be checked. If you decide to go the whole route and balance the clutch and flywheel, do so separately. Balance the flywheel first and then the pressure plate. The clutch disk can also be done separately. That way, if you blow a clutch, all you will have to rebalance is the replacement for the damaged part. Good luck with your rebuild!

PS: If you don't already have it, get Wayne's 911 engine rebuild book.