Board index Flathead Power-Technical Questions, Answers, and Suggestions Knuckles Knuckle oil return/smoking issues

Knuckle oil return/smoking issues

Post Tue May 20, 2008 5:12 am
So the Knuckle runs great - but is smoking when hot and the rear plug is starting to foul up. Was concerned with too much top end oil so restricted it with .080" jet, and cut the oil pressure spring to bring pressure levels down (S&S pump/crankcases). Also running the slower drive gear set. Not the problem though.

FHP heads rear intake valve cover not sealing, front exhaust cover not sealing (so obviously vacuum issues for oil recovery). The holes drilled in the top of the FHP intake covers concern me as well. How can the stock system draw a vacuum on the intake tins with holes drilled in the top? It appears that the intakes seem to be the problem as the intake ports are soaked in oil so I suspect the oil is not evacuating properly, thus overwhelming the seals. Comments????

My set of stock 39 heads have no holes drilled in the tins at all so what is the deal with the FHP design?

Any insights would be greatly appreciated.

And for those who own FHP heads do NOT try and remove the oil fittings installed into the cast valve "tins" - they snap off instantly. They are extremely fragile and appear to be red loctited in. Next question: where do I get a replacement fitting? I have never seen such fittings before.

Thankfully the bike runs and drives like a dream or this setback would be much more painful Crying or Very sad

Post Tue May 20, 2008 7:44 am

Posts: 62
Location: Texas' Big Bend country
Howdy Brent,

I have just completed a similar engine, although with OEM heads. Al at S&S suggested that I restrict the overhead oil line to .060" both at the rocker box fittings and at the crankcase outlet. I used the male halves of three thin brass rivits drilled to .060" and inserted into the flare fittings at the rocker boxes and crankcase. The thin brass skirt at the base of the rivits was formed over the taper on the fittings when I tightened down the flare-nuts on the Y line and have not leaked, nor have I had problems with too much oil to the heads. Easy enough to do and might solve your problem.

--- Randall

Post Tue May 20, 2008 10:08 am
Thanks Randall - have been following your posts as well.

Talked to Al this am - was very helpful. Am already running a restriction at the cam cover fitting - will try also at the rocker boxes. Al said not to go below .060".

What kind of oil pressure are you running? Al recommended 5-8lbs hot at idle maximum (using an accurate gauge eg: from a hydraulic supply house). He figured that 5 lbs is really all you need at idle hot since no hydraulic lifters and such. I am still running about 15lbs hot which he felt is still way too much so this might be an issue. No issues with leakage just smoking when hot and lots of pooling oil in the intake ports.

Post Tue May 20, 2008 11:01 am

Posts: 79
Location: No. Andover, Mass. USA
It may be that you have a vacuum problem rather than an overfeed problem. Rechech the pushrod tubes. The fact that it's leaking out the rocker covers leads me to think that pressure is building up in there thus making the gaskets fail. On my oem heads I do not have the holes in the tins. Going back through the files there are discussions on the merits of holes or not. My opinion is that they're not needed but that's me. If the vacuum is sufficient and feed metered the oil should be evacuated as soon at it drops to the suck out hole.


Post Tue May 20, 2008 11:57 am

Posts: 62
Location: Texas' Big Bend country
I have a mini oil gauge (3/4" face) screwed into the original overhead oil outlet on the cam cover and I suspect it may only be giving a general idea about the oil pressure. The pinionshaft is set up for end-oiling (constant flow) and the gauge shows 40-45 psi cold, rapidly dropping to 5-10 psi as the oil warms. I have made no modifications to the spring in the S&S billet oil pump. Al said that for end-oiling it would be necessary to split the top end and crankshaft oil circuit, which I did, taking the oil for the topend from the outlet hole behind the rear tappet block. I do not have a gauge on the top end circuit so I can't say what the pressure is there.

--- Randall

Post Wed May 21, 2008 4:40 am
"It may be that you have a vacuum problem rather than an overfeed problem. Rechech the pushrod tubes. The fact that it's leaking out the rocker covers leads me to think that pressure is building up in there thus making the gaskets fail."

Thanks Dick. The pushrod covers are sealed up tight - lots of vacuum at the rocker boxes. The rocker covers are not leaking oil - they are just not sealed 100% due to shoddy assembly when new. I can blow through the lines and hear/feel air escaping but they are not leaking oil.

Post Thu May 22, 2008 7:58 am

Posts: 35
Location: clear creek,id
brent,as you might remember i fought this problem all last summer and also had oil standing in ports and manifold,with presure set at 10 psi cold-2-3 psi hot at idle,i tried everything [too much oil-for more info].do the fhp rockers have them spiral groves in there brass bushing in them? if they do ,theres your problem.i pulled heads apart,i replaced bushings with solid brass ones,i have v-twin arms,[wanted fhp ones but couldn't ever get them to anser phone],these took shovel bushings,had them set up to a little over.0005 clerance to shaft,end of problem,i also put in seals on intakes an tightened up clearances to newer specs as cotten and others sug.,but i know it was those bushings. i now have presure set at 30-32 psi cold,20 psi hot at idle,about 25 psi goin down road,with no pluged an drilled to .060 fittings in heads or cover and have about 450 miles on it now.i can tell when i checked push rods that things are way dryer than they looked before,i never remember head parts lookin so wet before as when i took them apart,them groves allow to much oil to be fed to vavle and the solid bushings slow this flow down like the stock arms do.i hope this helps an i appreceate your help last summer.whoever came up with the idea for these groves in those bushings never tested them or they would know this,[as far as v-twin go,s]we are testin them for them,an payin a high price for there shit parts to boot.randell says s-s says to feed heads from feed behide tappet blocks so crank and head oil this split,is there less oil comin out there than would be if coming off timing cover? this has caused me hours an hours of work,lost ridin time,a bunch of i told you so's,more money, an you and a lot of other people the same to.all these problems are caused by the same thing-AFTERMARKET
Last edited by knucknutz on Thu May 22, 2008 3:56 pm, edited 1 time in total.

Post Thu May 22, 2008 9:43 am
Hi Knucknutz - glad you finally sorted out the problem and am out riding!

The FHP rocker arms have solid bushings -no grooves - so this is not the problem but thank you very much for the input. I have read and re-read your posts several times to make sure I am covering all the bases and had already checked for the spiral bushings. Thanks again.

Post Thu May 22, 2008 10:08 am

Posts: 62
Location: Texas' Big Bend country
Howdy Knucknutz,

Al at S&S said that we needed to split the bottom end and top end oil circuits because we had set the pinion bushing up for constant-flow end oiling as per the late engines. He said that the top end would be starved for oil if we fed it off the cam cover with this set up. Glad to hear you solved your problem; I've been following your posts.

--- Randall

Post Fri May 23, 2008 7:17 pm

Posts: 22
Well I have the same problem & found that FHP suck at building engine. Hope S&S does a better job of it and I think they will.

Ok some things to check:

1)Make sure the drain hole in the lifter block line up with the passage in the block ( my rear block was not drilled right it was a half hole off ).
2) Pull those damn upper oiler fitting out that FHP used they leak vacuum & oil making it look like the tins were leaking ( go down to the local model airplane and buy some new fuel line fitting for their engines , they work great).
3) double check the timing on the beather gear also the the breather hole should be 5/16" hole.
4) the hole tin plug it with some clear caulking for now it may help the vacuum ploblem.

I still have very small bit of smoke at the frist start up of the day but after that she run fine no oily plugs.
Plus I'm running 40 lbs at hot.
Hope that help.

Post Tue May 27, 2008 5:21 am
Update: so I pulled apart the FHP heads and its a good thing I did. The rear intake rocker had .035" end play, the front intake had .026" play, and each exhaust had about .020" play. I guess the guy with the body grinder who ground the ends of the arms got a little too sloppy and believe me, someone did use a grinder. Shovelhead rocker arm shims worked nicely to bring things back to spec. The outside of the arm themselves had been ground all to #$%@ obviously to clear the FHP aluminum covers. Even the inside of the top covers had been hit with a dremel tool for clearance issues. Crude stuff especially for what I paid. It is a wonder the aluminum covers seal at all once you see all the grinding and shaving that goes on just to make them fit. The clearances on the rocker arm to shaft were decent on the front exhaust (.001") and the front intake was good but the rear intake was just a mess. Approx .0015" clearance on the ball cup side and .004" clearance in some places on the the spring side bushing. In fact, some areas had .0015" clr, other parts the .004" clr. Completely out of round. The rear exhaust was too tight and would bind when the rocker shaft was tightened. Ended up having to enlarge the bushing with my pin hone to get the proper clearance and eliminate the binding. Most importantly I had to put .025" shims under the rocker housings themselves (between the housing and the head) so that the whole assembly wouldn't pull down and bind when everything was tightened up! I couldn't believe what I was seeing when doing a "dry run" without seals to check alignment and rocker arm side clearance. I checked everything possible and both heads were the same - either the holes in the heads (that the shafts pass through) were machined too high or the rocker housings had too much milled off the bottom. Either way the heads had been put together with a terrible "stressed" condition which could only have spelled trouble down the road when one of the ears on the heads eventually broke off (not to mention the binding rear exhaust rocker arm).

I guess I should have figured on this stuff - when the company takes your money and then doesn't bother to return your phone calls when you are wondering where your parts are, or bother to tell you when they take your order that you will have to wait months to get your parts - the warning signs are there. Just trying to get these people on the phone was a battle in itself.

Of course this is all post-Anders. I am sure that when he was at the helm the situation was totally different. In fact, when I ordered the heads I was under the impression that I was dealing with the original FHP and doled out the big bucks based on the company's excellent reputation. I had no idea of what was going on behind the scenes and had I known, would probably not have bought the product.

No wonder S&S is redeveloping the whole line - they would never have allowed product like this to leave the shop.

So: if you have bought a set of FHP heads recently I STRONGLY urge you to take them apart and spec them out before problems arise.

I still need to get my oil pressure under control and will update all once the bike is up and running again.

Post Wed May 28, 2008 3:37 pm

Posts: 22
When do the push rod tubes be sure to double up on the seal for both exhaust tube only it makes for a good seal and help make sure for a good vacuum.

Post Thu May 29, 2008 4:54 pm

Posts: 64
Location: Lancaster, SC
Did you find a replacement for the oil fitting that snapped? I have a smoking/leaking problem with mine after the mech. replaced the oil lines to the fitting.

Post Thu May 29, 2008 6:18 pm

Posts: 22
Yep, We when to the local model airplane store and got some little gas line fittings push the hose on works great and I have had to use any clamps. You may have to run a tap in to clean threads I don't remend what tap size was but it was a metric tap .Be sure to use a little pipe thread sealer too.


Post Thu May 29, 2008 9:18 pm

Posts: 64
Location: Lancaster, SC
Thank you .. I'll pass that info on to him, he's working to fix it now.

Post Fri May 30, 2008 5:11 am

Fittings for the FHP heads can be found at The part number for the fittings in the lower "tins" is STO-4 PKG. They have a 10/32 thread so be careful. Thanks to Al @ S&S for finding out this info for me. The new S&S heads may or may not continue to use these fittings - was told their "tins" are still in the development stage. The fittings that attach to the rocker box are 1/8 pipe with a swivel head (1/8" line) and can also be found at the Clippard web-site. Hope this helps anyone out there with this style cast rocker tin. The fittings are relatively inexpensive and they also sell a clear line so you can watch the oil return action to help control over-oiling/return issues.

Post Fri May 30, 2008 7:42 am

Posts: 64
Location: Lancaster, SC
Can you double check that part number, the Clippard search engine does not recognize it.

Post Fri May 30, 2008 8:34 am
STO-4-PKG. Try it with the "dashes". Their search function sucks. You might have to find it manually. I did the first time I tried to locate it. It is there.

Post Fri May 30, 2008 9:28 am

Posts: 64
Location: Lancaster, SC
I hate to seem dense but I can't find it. I Have looked in the pdf of their products under tubing and hose but there is no STO-4-PKG.

Post Fri May 30, 2008 9:53 am ... =ST0-4-PKG

This is from the Canadian site but their US phone number I believe is at the bottom of the page. For some reason I can't go to the US site.

This is for the swivel fittings that screw into the lower "tins".


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