Parilla Swift top end rebuild (JICA)

Kirk Deason · Last edited by Kirk Deason on Thu Mar 22, 2012 4:32 pm, edited 1 time in total

I was clogging up my previous topic of WB32 settings with my slow realization that the problem was not with the twisty bits on the carb. After testing the compression and finding *only* 55 or 60psi, I took the head off and found a stuck ring. I may have been able to simply clean the groove and put it back together but I went with a safer option and decided that a new piston and ring would be a better solution.

I measured the bore and came up with 52.39mm. After reading the Italian Motors' pdf and realizing that the bore came as a 52.40 from the factory i realized that my micrometer (or the operator) may be off a hair.

Claudio at IM helped me understand that a 52.40 red-dot was the piston I needed. It comes with a ring and circlips. I also purchased a new wrist pin bearing and all new gaskets.

Here are the goodies that arrived yesterday. Sorry about the glare:

Kirk Deason · Posted: Thu Mar 22, 2012 2:06 pm Post subject:

I measured the base gaskets when I removed them. The second picture is hard to see but there was a paper thin base gasket that measured at .25mm and a thicker one at .50mm.

and

(I fixed the giant size pics)

Kirk Deason · Posted: Thu Mar 22, 2012 2:08 pm Post subject:

The cylinder was unmarked and does not appear to need much attention.

and the bottom:

Kirk Deason · Posted: Thu Mar 22, 2012 2:10 pm Post subject:

My finger is pointing to the spot on the groove where the ring was stuck

Kirk Deason · Posted: Thu Mar 22, 2012 2:13 pm Post subject:

Pics of the head and combustion chamber.

Kirk Deason · Posted: Thu Mar 22, 2012 2:19 pm Post subject:

Circlip before removal--but here is where I got stuck and stopped last night. After the circlips were removed, I expected the wristpin to slide out with just finger pressure. I was wrong. It didn't budge. I tried pushing on it with a plastic pen but that didn't move it. I did NOT hammer on it or tap it with anything as I did not want to damage the rod.

I thought about adding some heat to the outside of the piston and then pressing on it again from the other side.

Does anyone have experience with this? Previous tricks or tips for wristpin removal?

Jim McMahon · Posted: Thu Mar 22, 2012 6:10 pm Post subject:

Sounds like the ring got gummed up alright, common enough with the nice smelling castor oils that get used in these motors. Looks like the piston is toast anyway with the dish in the center of it.

Like you said, if you heat the piston (I used to use a hairdryer) the wrist pin will push out. How is your main bearing axial and radial play? Did IM tell you what the squish clearance should be?
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João Costa · Posted: Fri Mar 23, 2012 1:39 am Post subject:

if you need some infos, i can tell you.

i have rebuild some engines like that and the last one i have made:
http://www.facebook.com/media/set/?set=a.296442357086232.69949.134690499928086&type=3

and if you make "like" on the Diabolicus page, you can follow many "threads" on karting themes

Wink

al nunley · Joined: 13 Nov 2006 Posts: 3030

Not being an expert on that engine, I can only guess, but that piston looks to be a mess.
What are all those markings around the outside edge? Is it detonation? Is the piston hitting the head? If it is hittin, that can be cause by too little deck height or a loose bottom end. What oil do you use? I’ve seen that stuck ring problem when using synthetics, but if the piston is hitting the head, that could also cause a stuck ring. Have you checked the main bearings? Any up and down movement? More than .001” is a lot! You’ll need a dial indicator and a holder to check that. It’s real important to know. Main bearings do wear out.
How are you checking the bore? Not with the calipers I hope. A bore gauge is best, but expensive. Expanding manderails and a good micrometer, (.0001“) will do the job.
If you’re not an engine builder, I would let one take a look at that engine.
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If the data does not support the theory, get a new theory. (Al Nunley)
All else being equal; Compression is the Holy Grail.
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Walt Gifford · Posted: Fri Mar 23, 2012 8:27 am Post subject:

Sometimes the wrist pin can move back and forth and push on the cir clip that raises a burr on the clip groove. You can try to remove the burr with a grinder but clean it good before pushing the pin. Try pushing it out by hand with a drift punch try both directions or very light taps with a hammer holding the piston by hand.

Put the piston a BDC. Put a piece of wood or metal between the piston skirt and the cylinder studs so the rod bearings are neutral then tap the pin out with a drift punch and hammer. If you think it's taking too much force then you need a wrist pin puller.

Don't forget to put the new ring in the bore and check for .012" end gap minimum.

Gif Cool

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Kirk Deason · Posted: Fri Mar 23, 2012 9:22 am Post subject:

Jim McMahon · Posted: Fri Mar 23, 2012 6:03 pm Post subject:

My question was about the crank though, not the rod. Grab the crank at each side and see if you can move it up and down. If you can you may need to replace the main bearings. Some axial play (endfloat) is desirable, something around .008" (.2mm). To test this grab the crank and try to pull it side to side.

Al has a point about the missing carbon on the periphery of teh piston, sounds like it may have been just contacting the head at times. Some would argue that for racing its almost desireable if small, however for testing practice you dont want this. Squish clearance along with good bearings, including main bearings is what will influence this. You can make small adjustments to the squish with either base gasket thickness or head gaskets.
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GPI Racing | WildKart | Maxter | Hoosier
Karting Festival @ Blackhawk Farms June 1st-2nd.

al nunley · Joined: 13 Nov 2006 Posts: 3030

Jim Russell, Jr. · Advertiser Joined: 03 Oct 2001 Posts: 1535

Looking at the pictures I agree that piston has been making head contact. This is not good at all. It will cause the stuck ring.
Causes-
improper machining
Improper assembly
too much wear on one or more parts in the rotating assembly

To push the pin out we use this tool
http://storefront.russellkarting.com:8080/storefrontCommerce/itemDetail.do?itm_id=3866&itm_index=0&orderQty=1

Our store can also help you with the parts that are needed. We can also do the engine work. Having been an IAME importer since its inception we can help you get the most out the engine within your desired results.

Jim jr.
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Kirk Deason · Posted: Thu Mar 29, 2012 8:19 pm Post subject:

The lower rod bearing is hosed. The rod play is more than excessive and it does not rotate smoothly around its complete stroke.

I think Jim Jr. nailed it when he said "too much wear in one or more parts of the rotating assembly"

I heated the piston with a hair dryer and with a few light taps with a drift and a very light touch with a hammer, the wristpin came out. Once the piston was removed and the wristpin bearing was out, I could get a good look and feel of the rod and main bearing. Verdict? Hosed. The movement that I was misinterpreting as the piston just being 'loose' was a toasted main bearing.

I took close ups of the piston which I will post tomorrow.