Any guidance?

[EricGlover]

I'm constructing a 78 x 100/2400cc engine with Brothers Machine heads featuring 44 x 38 valves and dual springs. I've installed a 186/86b cam with a 104 lc. The static compression ratio stands at 10.2:1, and I'm using 5.325" H beam rods. During the bottom-end mock-up, I've observed that the #4 rod is making contact with the cam. Although the cam has a smaller base circle and is supposed to be suitable for up to a 78 stroke, I'm glad I've triple-checked everything. My question is, could I adjust the cam timing by retarding it by 4-6 degrees instead of modifying the rod ends for clearance? I believe this adjustment might shift the power band upwards by several hundred RPM, which would be suitable for my application. This engine is replacing a Porsche 616 that produced power between 3000-6000 RPM. Any input on this matter would be greatly appreciated.

[Steve Arndt]

Profile / sand the rod big ends for clearance then re-balance them.

[wreck]

do you have the rod angled correctly , fitted a piston and cylinder (no rings) ?

[Eddie010]

Goodday,

I have almost the same set up, 78x100, with 5.315 inch H rod, webcam 86B cam 108LC with 4 dgr advance.
But no interference al all. Checked all the clearances, all were more than 1.0mm and rotating freely.
Do you mean you want to retard the cam instead of advancing it.
You have to bare in mind that cam is turning counter clock wise.
Did you clock the camlobes of nr 1 cylinder with TDC. with this set up.

Hope this helps.

Ps the power band on my 86B is already in 3000-6000 range, why do you want it to be higher? (retarding it).

[Ol'fogasaurus]

https://www.bing.com/search?q=retarding ... 57e5528fa6

For what it is worth

Lee

[MegaRookie]

Luckily you tripple checked e everything. What rodsize are you using? T4, chevy or type 1? I also had some clearance issues with building my engine, but that was 86 stroke, 5.7 (t4 cromo rods with arp bolts) ans 86c @ 1" base circle. What base circle does your cam have?

Depending on the rods you used I would modify them for enough clearance. Be sure to double check the base circle, and make sure you check the clearance by using the piston and cylinder.

Mark

[suspecttest]

Hi Eric,

Adjusting the cam timing by retarding it 4-6 degrees could be a good solution to address the clearance issue. It might shift the power band a bit, but it seems like a reasonable trade-off for avoiding modifications to the rod ends. Just be sure to double-check your timing marks and re-tune if necessary. Good luck with your engine project!

[Type 4 Unleashed]

I agree, somethings not right. The only thing I can think of, is your running Type 1 jrl's and your rods are using 3/8" bolts.

And as was previously mentioned, for a mock-up you need to use a piston & cyl, so the rod is at the correct angle as it passes by the lobe, it can't be properly done by hand. And I don't recommend trying to adjusting cam timing to provide rod clearance, can cause other issues not to mention there is no benefit for all the extra work.

For comparison, here is a pic of a mock up of one of my projects, that I will finish one day. Cam was either 1.1" or 1.080" base circle, 84mm stroke with Type IV 2.0 ltr jrl's( 1.967"-49.96mm) with 5.7" rods with 5/16" bolts. I am happy with a .040" minimum clearance. And there is piston & cyl at the end of that rod. And the rod is not stroker clearanced.

Read the post by 77Westy at this topic, which should show that you have some issues.
viewtopic.php?t=152749





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