nick49

Good work and nice write up!

I'd mention the greatest area for a potential problem is in the wrist pin clips. After installing them all, measure the ID of the installed clip with a dial caliper. If any are smaller, that means it's not seated fully in the groove and may back out. This could be due to a wrist pin being a bit too long, insufficient depth of ring groove or just the clip not being fully seated.

Also from your earlier specs, bore of 3.8976 and piston size of 3.8945, this yields a clearance of .0031, your specified clearance is .0035. You're on the tight side of the spec. and I realize it's +- .0005. Being a bit tight is OK but break in will be more critical and you could develop a bit more heat in the process. For this reason I'd give a couple of more thou to your ring gaps. This will be a safety valve and eliminate a potential ring butt failure. The recommended gaps are generally the absolute minimum and I like to give a bit more, say .002-.004+ for both the top and 2nd. This is good insurance and gives you a cushion. I've seen many motors with collapsed pistons and scored cylinder bores just because a ring butted. A couple of extra thousanths of added ring gap would have prevented this.

Another couple of points, check the sharp edges of the machined piston pocket edges on the crown. If these are sharp, radius the edge very slightly with a stone or crocus cloth. The sharp edges can cause detonation from glowing heat.

I also started assembling pistons and rings dry about 35 years ago. Assembly lube on the pin and a spot on the thrust faces of the pistons, dry clean bores, dry rings and grooves. Many long time builders do this, many still oil everything up fully.

In building motors, more info is better. Make your decisions based on hearing opinions from those in the trade that build successful motors. Decide what is right for you. Not trying to tell you what you should or shouldn't do, just passing on a bit more info to chew on.

GL!

logray

Thanks for the tip!

This has been on the back my mind too. I am going off what LNE is instructing since they finished the cylinders and provided the piston specs to JE.

edit: the piston/wall clearance is to be set to .0035".

I'm still chewing on the numbers myself, but here is some more info to throw out.

There is a coating on the piston skirt where the measurement is taken which might add .0005 according to LNE.

The bore spec is 99mm, which is actually .0000378 larger than 3.8976.

JE recommends minimum end gap clearance of appx .0043-.0045 per bore inch for this product. Which works out to something slightly different than what LNE recommends.

Top .017"
2nd .018"
Oil .015"

I inquired whether to use those numbers since it was somewhat unclear based on some other instructions and was ultimately provided .015 top, .016 middle, and .015-.016 for oil. The oil rings were already within that range.

This isn't something I want to screw up, and I do appreciate the advice. It's easy to remove material but adding material back means ordering a whole new set of rings.

I gave them a once over after the machine shop checked/recommended the same thing. There was one piston that needed a little deburring. The rest are smooth as butta.

Interesting. I wonder if that is based on the application you were using (CI?), and Nikasil warrants oiling it up. Everything I've read for this specific product says to lube it up to promote ring seat/seal. These are recommendations from both LNE and JE.

JE:
"We recommend a light coat of non-detergent oil on the piston's skirt and cylinder walls for initial installation. DO NOT USE DETERGENT OIL, SYNTHETIC OIL, OR AN ADDITIVE until the rings have seated."

LNE:
"We recommend a light coat of non-synthetic oil motor on the cylinder walls for initial installation ... Do not install the rings and cylinders dry!"

Porsche factory manual recommends the same thing.

pterfloth

I attended the M96 101 Engine Building school at Flat 6 in Sept. Jake recommended grinding off the hook on the wrist pin clip flush with the clip. The potential for not lining up the hook with the hole is too great and if the wrist pin clip falls into the carrier during installation, the carrier will often need to be disassembled to find it. All the wrist pin clips we installed had the hook ground off.

For 99 mm bored engines Jake recommended 0.015 for the top, 0.016 for the second and 0.015-0.016 on the oil ring.

logray

Wow thanks. That really restores my confidence on the gaps.

So you mean to say you ground the hooks on the clips completely off, so they are in a sense round, with no tang?

pterfloth

Yes, the hooks were ground off flush so that the clip is a perfect circle. That way, the hook can't get hung up and pop off if it isn't aligned perfectly. Lining up that hook would be tough.

Here's a picture from the course that shows a clip that has had the hook ground off. (sitting between the 2 wrist pins)

logray

Wow! What a marvelous idea! This will make the 4-6 insertion much less painful. I think I will still keep the hooks on for the other 9 clips I can see easily and do on the bench.

Thanks for sharing (and of course thanks to the brains behind it if you are lurking.)

Next week I'll order a new set of clips for the 1-3 pistons I'll be re-doing. Since I shouldn't be re-using clips that have already been installed.

Quadcammer I owe you one for bringing this subject up!

nick49

Another tip:

warming the piston with a heat gun/hair dryer will make it so you can drop the pins in place and push them through with a finger. If the pins are a light press or interference fit in the rods, warm them too. This will preclude the use of the driver and hammer. If after warming they are still a bit tight, chill the pins in the freezer for a few minutes.

Use a straight seal pick as a lever tool to install the clips. You'll get to where you can snap them in place in a second or two, first time every time effortlessly. I'd still verify the clips are fully seated by measuring the ID.

pterfloth

I'd also keep the hooks on the easy clips. Its the last 3 that I would grind off.

logray

Thanks again! I certainly will carry out those measurements (except for 3 of the clips that are done blindly a foot deep in the case where that would be nearly impossible).

The fit on the wrist pins is very tight, like .0005 to .001. The machining tolerances are impressive to say the least! A careful hand is all that is necessary.

As for installing the clips, I'm still not sure what the "best" method is. I've read that some can do it with brute finger strength, others with strange angles and twisting, and others still the use of tools. I'm pretty sure tools are the answer and I wouldn't disagree that a pick would be a good tool here. If you've seen the tool that inserts the clips over a foot deep into the 4-6 pistons after they are installed in the case, it might become more clear. So far, this appears to be the best method... the clips are not twisted, yet compressed in a similar fashion that is required to place them into the insertion tool (if that makes sense). If the tool is good for installing 3 of the clips, then it should be good for the rest.

Quadcammer

Installing wrist pin clips was my least favorite part of engine assembly. Those things are finnicky and a real pain on the finger.

With respect to ring gaps, I always tended to aim for the looser end of spec. With high oil temps and extended tracking, I like the additional gap, even with slightly higher oil consumption. A butted ring does some really ugly stuff.

rb101

If you leave the hooks on the other 9, is the difference between cut and uncut weight going to throw off your balance? Or is it to small an amount?

logray

Just guessing but the clips are probably worth a couple grams, and the hook might be worth 5-10% of that. I could do the same on the other bank to even it out.

Anyways, I'm contemplating keeping the hooks in place, since it's my car and my time if I have to crack the case open to fish for clips it's not the end of the world.

logray

Update:

Two steps backwards and one step forward.

I received 4 of the replacement 6 clips that I need, there was a slight mix up when I said I need three packs of 2 (and they charged me for three clips and sent 4 rings or two packs of 2). The other 2 clips are to arrive Tuesday, along with... tada!

(image courtesy F6I)

I was at a point in the rebuild where I had to make the decision which had been on the back of my mind since the get go. Yes I already dropped some pistons into the cylinders, but call it an anxious test fitting or what have you (I'm over it and thanks again) . I blew the budget and ordered a set of R&R rods from Charles to arrive next Tuesday. I couldn't bear buttoning this thing up and driving her around for 10 or 15 years with brand new everything pretty much but my same old tired rods.

During the idle time waiting for the clips and rods I also had a chance to mull over another potential issue while re-measuring everything for the 15th time. This issue did not come up during the initial test rig fitting.

On the other case half that I had not yet assembled, I test fitted all of the rings again. What I discovered was that the oil rings seem to be a few .001" too small. When I say "seem", it is REALLY difficult to get a precise measurement with a .015" feeler gauge. The gauge "fits", but not apparently without slightly distorting or moving the oil rings out of alignment. It is very very difficult to say this with certainty and a straight face though, as there is a small amount of oil in place while taking the measurement to help keep the oil rings from moving, perhaps that oil is throwing things off. The oil rings are extremely thin, and don't have much spring to them, so just resting in the cylinders there is a small amount of clearance between them and the walls. I can square them up fine, but as soon as I attempt to get a feeler gauge in the gap the rings move ever so slightly. The only ones I can fit in without them moving are the .013 and .014 gauges, but even then it takes more than a steady hand and my measurements are sometimes skewed if I barely touch one of the rings with the gauge.

Here's where it seems to get a little weirder. I tore down and cleaned the other cylinder half and re-measured those as well. Same thing! Every single oil ring in every single cylinder has the same problem. They all appear to be about .001 or .002 smaller than the recommended .015".

Now I'm not adverse to filing every single oil ring (as I have already done with the top and second rings), which will be difficult since they are so thin, even with a dab of oil the piston filer might chip the face so I might have to remove the .001 or .002 "by hand" with a wet stone or jewelry file. But it does strike me as odd that not even a single oil ring is correct. Perhaps JE messed up the machining or sent the wrong rings or LNE didn't finish the cylinders at 99mm???

I did measure the cylinders at .0001" smaller (3.8975") than LNE did (3.8976") during their quality check, and 99mm is .0000378" larger than 3.8976". End gap measurement does change by a factor of Pi, so perhaps the math does work out if my measurements are right.

If the oil rings were made to fit a 99mm bore based on a .015 gap, and the cylinders actually measure out to be .0001378" smaller than 99mm, that works out to .0004" less end gap. Which might explain why the .014 fits but the .015 does not appear to.

Even though I'm working at 68F (JE recommendation), I'm wondering if perhaps that is not right either, and it's supposed to be 72F as I read elsewhere and may account for a few .0000x" skew of the measurement as well.

All of the cylinders are extremely close though. I can pretty much interchange any of the rings I custom filed to the other cylinders and they are almost dead on (with the exception of a couple that are slightly larger).

Now obviously I don't want rings ends to butt, and I am guessing everyone will suggest to file them down and wider is better... however does anyone find it odd that not a single oil ring appears to be correct from the factory?

Comments and suggestions are much appreciated !!!!!!

Charles Navarro

With the slight temperature differences and typical measuremt errors that can occur when dealing with units this small, I would feel safe to just run the oil rings the way they are (unless you plan on starting up the car in the artic circle). We often run ring clearances much tighter than the published specs without issues, so don't loose any sleep over the oil controls being .001" small.

nick49

I'd actually be more concerned with where your compression rings are now. As stated before, I'd open up the top maybe .002" .003" more for good measure, and have the second at least 2-3 thou larger than the first. This additional amount will not cause any compression loss at all, just a huge safety valve if one cylinder or more happened to run a bit hot for any one of many reasons which they can. These include a partially clogged injector, slight blockage in water passage, blockage in oil cooling jet , air leak in intake and several others.

Very slightly tight oil rings are not nearly as serious as tight compression ones, that's because that portion of the the piston is much cooler than the crown that is in contact with the hot combustion gasses. Where the danger lies is if a compression ring gets a bit tight, friction dramatically increases, which in itself causes much more localized heat that makes the piston swell to the point of seizure. This ruins the piston and often the cylinder surface as well at the very least.

This is not a go kart motor that you can fix for $50 and 2 hours if something goes awry. I can see you're full of questions and certain amounts of uncertainty. Make it easy on yourself and clear all the doubt. Doing this stuff for a living since the '70s, I know that every motor will start instantly, sound terrific, and no noise or smoke before I attempt to start it for the first time. It's knowing about potential problem areas and addressing them and removing all doubt during the building process.

Drag the oil scraper rails on a stone a couple of times till you can push the .015" blade in there and if you're so inclined open up the compression ring too. I would, you'll sleep better.