RE: Piston orientation after rebuild

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highlandmurf
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RE: Piston orientation after rebuild

Post by highlandmurf » Thu Mar 25, 2021 10:56 am

Hi All,
So I had my bottom end rebuilt last year, by a shop that I have lost all faith in.
He did not due his due diligence in several ways, and I am not feeling confident that I have a reliable engine.

All grumbling aside, now that I have this thing broken in- Stock 2.0 solid lifters. The engine is very loud at cruising speeds.

Details:
1) I did a top end rebuild about 1000 miles prior.
2) Dropped off a short block. with the pistons and jugs attached, as I wanted him to inspect the wrist pin fitting.
3) I think the new wrist pins did not like the existing rod bushings leading to noises, prompting me to have the case rebuilt.
4) Pins were found to be rocking in the rod bushings.
5) Rods and crank were sent out to 3rd party/s for grinding, polishing, pressing balancing.


As I said, the engine is loud. I think if it was out of balance, this would be evident at idle.

It has an extractor exhaust, which is louder that I would prefer, but I believe it is much louder than I remember.

I am confident that I checked the piston arrows to flywheel carefully. I believe the heads are properly tightened
(Engine was in and out 3 times troubleshooting leaks. Heads off twice. Was just as loud on both test runs)

Question:
Is it geometrically possible that the rebuilder flipped the pistons side to side- i.e. #2 is # 3 and #4 is #1 piston?


In this scenario, the wrong piston would still point to the flywheel.
'76 Westy Marino Yellow

cjacaruso
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Re: RE: Piston orientation after rebuild

Post by cjacaruso » Sun Apr 11, 2021 7:38 pm

Hmmm. I'm rebuilding my 2.0 right now. I just put new pistons on. There is no designation as to which piston goes to which location with new. With used, 1000 miles it sounds like, it is best to put the pistons back in their original location. Why, I don't know. With new, as long as the arrow is pointed towards the flywheel you are good. So to answer your question, I don't think even if pistons where repositioned it would matter a whole bunch. As to the noisy engine, it could be the bearings are not fit correctly. I had a professional builder machine my case and give me the "correct" bearings for cam, crank, and rods. When I assembled the engine case and checked things I found I had the wrong rod bearings and they were one size too big. That would have caused a lot of noise! Another possible issue would be the wrong cam gear. There are a bunch of sizes of these, -4, -3, .... 0, +1, .....etc. 9 different sizes. If your builder was not careful and you have a misfit cam gear that would also possibly cause a bunch of noise. It would work though and eventually wear itself in. The cam gear is either aluminum or magnesium (soft) while the matching crank gear is steel (hard). You did not mention end play. Is that OK? That too could cause noise. These are all bottom end issues.

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highlandmurf
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Re: RE: Piston orientation after rebuild

Post by highlandmurf » Mon Apr 12, 2021 6:29 am

Just to follow up,

Had the bus out for it's first local drive, some highway, some county/local roads.
Engine is at it's loudest, at 38-48mph in 3rd, quiets down at highway speeds in 4th.

The extractor exhaust is loud. Perhaps, I forgot how loud. Planning on going back to a stock exhaust, as soon as I can find a good crossover pipe.

In summary, I am thinking everything is ok, as I can't see the engine only having an issue at that rpm.

Thinking my lack of faith in the rebuilder has got me a little paranoid, and the engine was louder than I recall.

Will have some more spring driving in soon. we'll see.
'76 Westy Marino Yellow

cjacaruso
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Re: RE: Piston orientation after rebuild

Post by cjacaruso » Mon Apr 12, 2021 8:19 pm

Good news! They are noisy beasts. Get a good sound system and all will be well!

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Amskeptic
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Re: RE: Piston orientation after rebuild

Post by Amskeptic » Sat Apr 17, 2021 7:01 pm

cjacaruso wrote:
Mon Apr 12, 2021 8:19 pm
Good news! They are noisy beasts. Get a good sound system and all will be well!

A good balancing job helps. To make sure that your engine is not horribly out-of-balance, just kneel back there with one hand on the fan housing and the other on the throttle lever. Easily bring engine off idle to about timing speed (3,400 rpm) and let it come down.
*Bad balance is noticeable on the decel side right around 1,200 rpm.
*Roughness on the way up can be cylinder power deviations.

Sorry about your troubles!
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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