Christmas Build, 3.2 Short Stroke, 10.1 CR

[snbush67]

The engine is in.

[Old H2S]

Zoom zoom..

[snbush67]

Engine is running. Changing the jetting and fixing an oil leak. Missing a crush washer at the oil pressure sender between the block and the case.

[Old H2S]

FAIL..Tear it down and do it again.

[Joesmallwood]

Saweet!!

[snbush67]

Break-in is done, leaks have been eliminated. Butt dyno tuning begins.

Started with PMO 46 on normal height manifolds/42chokes/ F11 tubes/ 187 Fuel/ 187 Air/ 57 Idles.
13.6 at idle 950
12.7 through 2800
14.6 - 18.0 through 3500 (this isn’t good, small hesitation, bumpy, at light throttle)
13.6 - 11.4 through redline (7000)

Changed fuel jets to 200

12.8 at idle 950
12.5through 2800
13.6- 17.3 through 3600(this still isn’t good, still small bumpy blurps)
13.6 - 10.0 through redline (7000) (this is to fat)

Installed the 123 distributor with MAP connected and that smoothed things out a bit.

Still have a mid range lean flat spot 3200-4000 rpm.

I’m going to continue with the 42 chokes, but may go down to 40’s.
I’m thinking of trying F2 tubes and maybe bumping the idles up to 58.

The lean flat spot is during the progression between closed throttle and the main jet circuit. So I’ll add a bit more fuel to smooth out progression between closed throttle and acceleration and for part throttle driving. And probably go back down to 185 fuel jets

[Old H2S]

I had to jump up to a F7 E tube to get it rich enough for the transition.

[snbush67]

Originally Posted by Old H2S

I had to jump up to a F7 E tube to get it rich enough for the transition.

Thanks, I have F7’s, I’ll try them too.

[trond]

apart from getting the carburettion right, what are your impressions so far. I have same cams on order and similar engine configuration and am interested in how the combination works. Did you check cranking compression numbers ? I have a 9.5CR and also a 10.5CR piston set and need to make a decision on which to use.

[snbush67]

Originally Posted by trond

apart from getting the carburettion right, what are your impressions so far. I have same cams on order and similar engine configuration and am interested in how the combination works. Did you check cranking compression numbers ? I have a 9.5CR and also a 10.5CR piston set and need to make a decision on which to use.

I have not done a compression test yet. It’s on the to do list.
Impressions are good at 10.1, I’ve ran an advance curve of 30 to 7000 rpm’s on pump gas, single plugged. No issues.

The short header length (primary tubes are 17”) are great for top end, there’s plenty there but I want more bottom end snappy torque, to rip out of tight uphill corners in second gear. I’m probably going to go down to 40 chokes in the carburetor’s to get that, maybe sacrifice a bit of top end.

But there is gobs of power everywhere. Zero complaints.

[Veeveessees]

Nice project…

[snbush67]

I heard a tick and shut the motor down. Drained the oil and some metal came out.

Turns out the engine spun a bearing.




So now I’m starting over. I’m happy knowing that I heard the ticking noise and shut it down before serious damage. It could have been a lot worse.

[911 tweaks]

good catch...!!
when you were building the engine, you obviously did not feel any resistance when by hand rotating the crank... so, defective part or what do you think happened...?
Hang in there Shane...
Good things come to those whom are good people & you are one of the good guys...

[PeteKz]

That sucks. I sure want to know what happened too.

[snbush67]

I’m really struggling to find fault, the bearing clearances were at 1.8 thousandths, the rods dropped effortlessly with their own weight but did have a slight drag.

The engine rotated smoothly.

Until after the ticking, that’s when I took out the spark plugs and did a leak down. Then I noticed a drag at 20 degrees before tdc for #1 and #4 so it was pretty clear it was at the crank.

When I removed the cylinders and rotated the engine #5 rod was hanging up.

I can’t believe that there was anything left behind in the oil lines but I guess that’s possible. Just don’t know.

The oil was clean, like new, and all the metal I found was right at the sump plate and a couple of small pieces on the sump screen.

Before the first start the oil pump was primed and then I cranked without spark several times for 10-15 seconds.

I think it’s likely the clearances may have been a little too tight and perhaps some debris.

The good news is that all cylinders had less than .5 leak down cold.

[mikedsilva]

I don't think 1.8 thou is the cause of the spun bearing.
Put the rod together and torque it and measure the big end again...

[snbush67]

Originally Posted by mikedsilva

I don't think 1.8 thou is the cause of the spun bearing.
Put the rod together and torque it and measure the big end again...

Hi Mike. Nice to have you drop in.

[mikedsilva]

ah.. no.. you need a bore gauge and micrometer to do this. Vernier calipers are not for this sort of measurement.

[snbush67]

Originally Posted by mikedsilva

ah.. no.. you need a bore gauge and micrometer to do this. Vernier calipers are not for this sort of measurement.

Yes, I need a bore gauge. Tom (oldh2s) mentioned that to me that the rod end possibly wasn’t round.

That’s why I’m taking Williams recommendation and using new corrilo rods. Should have just did that the first time. I’ll also be bumping compression up and twin plugging.

[Old H2S]

The ISO horror stories I could tell from 1 bad caliper out of 50 in my company..and 10 turned out to be counterfeit Mititoyo. Switched to Mahr when it absolutely had to repeat every time. I forced metrology QC every week and carried a ceramic gage block in my pocket to spot check every time I saw a chance, crushing peoples personal tools with a hammer to get it through peoples heads "zee vill do it ziss vay" I had to be the maintenance Nazi, the lost hours haunt me 25 years later.