Author Topic: Re torque? (Read 1162 times)

750K5 · « **on:** February 13, 2020, 07:06:30 AM »

When assembling the head on a 750 with a standard head gasket I am aware that re torque is required. Can this be done after the head is initially torqued say over a 24 hour period? Does the engine need to go through heat cycles before re torquing? I'm trying to decide if I want to purchase an MLS head gasket from cycle X. I already have a standard gasket. I have also considered a frame kit after reading other thread topics. Where can I allocate a frame kit that will fit a K5?
I'm sure these questions have been answered before I'm just having a hard time searching for this info.
I appreciate any thought or info you may have!
Thanks

newday777 · « **Reply #1 on:** February 13, 2020, 08:32:52 AM »

Yes retorque the head after heat cycle.

Several places to buy the kit from

http://forums.sohc4.net/index.php?topic=15329.0

https://carpyscaferacers.com/shop/shop-our-store/motorcycle-parts-accessories/honda-cb500-cb550-cb750-parts-upgrades/frame-adapter-honda/

PeWe · « **Reply #2 on:** February 13, 2020, 08:53:18 AM »

Retorque after 24 hours is a good idea. The gasket compress so the nuts will move rather much.
You can wait another 24 hours and tighten again.
Back in the 80's I retorqued after 500-1000km. Not fun to pull engine again... ;(

Today Franks(forum member 754) weldless frame kit on both my CB750 if need to tighten or removing head.
I have trusted the retorque 24 hours after and eventual another one the next days or week. No hurry winter time.

pjlogue · « **Reply #3 on:** February 13, 2020, 09:02:59 AM »

Re-torqueing the head after a heat cycle is ideal however on a 750 it sure isn't practical as it would require taking the engine back out of the frame. The best thing to do is check head gasket thickness vs the Honda gasket. If it is thicker you will need to make adjustments for the oil orifice O rings. When I have replaced the head gasket I have made sure all head bolt threads are clean and oiled and torqued the head down to spec. Waited a day and re-torque. I have not had any leakage the two times I have replaced the head gasket.

-P.

BenelliSEI · « **Reply #4 on:** February 13, 2020, 09:08:16 AM »

+1 to pjlogue. Haven’t had any problems.

bryanj · « **Reply #5 on:** February 13, 2020, 09:21:43 AM »

Head gasket thickness has no effect on pucks but yes on O rings. Back when working on them full time in the 70's we never re-torqued just tightened to Honda spec with an accurate torque wrench, dont ever remember having to re do one.

pjlogue · « **Reply #6 on:** February 13, 2020, 03:34:01 PM »

Quote from: bryanj on February 13, 2020, 09:21:43 AM

Head gasket thickness has no effect on pucks but yes on O rings. Back when working on them full time in the 70's we never re-torqued just tightened to Honda spec with an accurate torque wrench, dont ever remember having to re do one.

You are correct about the pucks. Thanks for the catch. I amended my post.

-P.

750K5 · « **Reply #7 on:** February 13, 2020, 05:55:36 PM »

Thanks for all the feedback. I'll run with the gasket I purchased. It came as a complete kit so hopefully the o rings are correct. I saved the old gasket so I'll measure tomorrow. Should I expect that the gasket removed will be slightly thinner because its been compressed?

scottly · « **Reply #8 on:** February 13, 2020, 09:42:41 PM »

I have NEVER re-torqued after heating cycles; Honda certainly didn't, nor did they wait 24 hours.

PS I have weld-less frame kits ready to ship.

http://forums.sohc4.net/index.php/topic,180860.0.html

DaveBarbier · « **Reply #9 on:** February 14, 2020, 02:22:53 AM »

I also retorqued after 24 hours but not after any heat cycles. Just keep the engine on the bench, wait 24 hours and torque again.

tlbranth · « **Reply #10 on:** February 16, 2020, 04:43:46 PM »

When my bike was new, the engine was not removed to re-torque the head bolts.

PeWe · « **Reply #11 on:** February 16, 2020, 08:55:15 PM »

The typical CB750 head leak showed up?

bryanj · « **Reply #12 on:** February 17, 2020, 12:13:00 AM »

When working for dealers in the 70's i never had to pull any head for oil leaks

PeWe · « **Reply #13 on:** February 17, 2020, 01:49:23 AM »

My K6 got new head gasket after around 20.000km due to oil leak.
Not very much but enough to look dirty, flowing everywhere by the wind.

bryanj · « **Reply #14 on:** February 17, 2020, 02:01:10 AM »

How many years?

PeWe · « **Reply #15 on:** February 17, 2020, 07:47:09 AM »

I bought the bike early 1979, pulled engine for head gasket following winter.
Bike is shipped from Japan 1976.
Edit: Bike was stock back then.

bryanj · « **Reply #16 on:** February 17, 2020, 08:41:38 AM »

So it was 20,000 km and 4 yrs old before it leaked, i would call that reasonable

PeWe · « **Reply #17 on:** February 17, 2020, 09:10:14 AM »

I'm convinced that todays knowledge thanks to this forum will make it dry much longer.

tlbranth · « **Reply #18 on:** February 17, 2020, 09:48:44 AM »

Quote from: PeWe on February 16, 2020, 08:55:15 PM

The typical CB750 head leak showed up?

Long time ago but there always seemed to be oil leaking a bit in the head area. I have the engine out right now and wonder if it's worth just doing a re-torque. It was about 20k miles ago I put rings in.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #19 on:** February 17, 2020, 12:39:55 PM »

If you take it down to the top of the jugs you may consider using MLS gaskets. They are not "supposed" to need a re-torque

PeWe · « **Reply #20 on:** February 17, 2020, 11:22:27 PM »

MLS and RCS are fine if the surfaces are smooth without any leaking scratches.
The MLS gasket rivets must be checked too if located on the mating surface.

Retorque needed if base gasket is fiber that compress a little.
If base gasket is RCS, it will not compress.
Very thick o-rings another thing that compress in need of retorque.
I had to retorque my K2 engine 3 times due to fiber gasket and 8 thick oil return o-rings (Nitrile 2.5mm) when using late gasket on early cylinder.
Used thinner viton o-rings (1.78mm) next time when I replaced head a year later (last season).
Only 1 retorque 24 hours later, nuts did not move much, stiff feel, not spongy feel as before.

Same type of fiber head gasket. APE cyl studs, nuts tightened around 20 ft lbs (stock type of pistons).

I have now 12.5x2.0 mm viton o-rings for next time.
10.78x2.62 mm for the 2 oil feed for better match with thicker gasket.

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Author Topic: Re torque? (Read 1162 times)