Engine knock at idle

[squirebill]

In my Parts book for 1949, it shows a wire spring clip at each end of the gudgeon/wrist pin.  If my memory serves me right, there is a groove in the piston where this spring clip is installed.

[Sniper]

8 hours ago, Bryce Mcclintock said:

Pressed into piston or rod? 

Into the rod

[Merle Coggins]

That pin shouldn't be a press fit into anything. As stated earlier it should push in easily with thumb pressure. Circlips retain it into the pistons and the connecting rod should be able to float on the pin. Small end bushing in the rod should get lubricated via a passage between the big end and small end. 

[kencombs]

Yeah, 'press fit' with thumb pressure at room temp is a free floating pin when warm or after normal wear.  Pins are located by the mentioned wire clips.

[NickPickToo]

On 4/19/2021 at 7:44 AM, Tooljunkie said:

Crank thrust bearing, or something clutch related. You just never know 

I was chasing down a knock on my p-15 a few weeks ago and it turned out to be clutch related.  In my case the clutch peddle adjustment wouldn't release enough to allow the clutch to fully disengage.   When I fully pressed the clutch the knock would go away.  From over the engine it sounded like a knock coming from the front to center of the engine, but inside the cab it sounded like it could be the clutch.  I modified the clutch adjustments to allow more slack to be taken out and I added a stronger return spring on the clutch throughout lever.  This fixed the knock. 

[Bryce Mcclintock]

I did try pushing clutch fully in when i had engine running seemed to make no difference to knock . I took piston and bearings to mehcanic for second opinion he said it all looked perfectly fine obviously used but plenty of life in it he suggested what i may be hearing is piston slap and to get the piston expanded and see what happens ? Your thoughts ?

[NickPickToo]

Any advice from me regarding the inside of the engine would be, well.   But, there is a HP bonus to enlarging the cylinders, so I'd say go for it.  Not sure your location, but I had the inside of my engine done at Adams in Howell MI.  Great father son team and reasonably priced. 

Edited May 18, 2021 by NickPickToo

[Bryce Mcclintock]

Thanks im in New Zealand 

[NickPickToo]

Yes,  The shipping would do you in for sure

[Bryce Mcclintock]

So i have all pistons out of plymouth everything seems to be fine but the crank seems to me to have a lot of end float. book calls for a maximum of .oo7 of a inch play i dont work in inches but looks to be a atleast a millimeter of play to me i need to get something to measure it properly yet but would excessive play in crank cause a knock? How do i fix this excessive play ?

[kencombs]

End play is controlled by the main bearing that has the thrust surfaces on the side. I guess it could cause a knock under some circumstances but have never encountered that symptom.  If it was happening,  holding the clutch pedal to the floor should stop it as it would hold the crankshaft forward.

[Sniper]

.007" is .178mm. 

 

If you have a millimeter+ of play you have a problem.  1mm equals .039".   That's 5.5 times the max allowable clearance.

 

Hopefully the issue is a worn thrust bearing and not the thrust surfaces on the crankshaft.

 

Worn thrust bearings can be placed, one of the main bearings (the one with a flange) is the thrust bearing.

 

Worn trust surfaces require either a different crankshaft or having you old crankshaft welded and ground back to spec. 

 

However, having that much play in your thrust makes me wonder what it did to other components, i.e. rod side clearances, bearing edge loading, etc. 

[Bryce Mcclintock]

Can i replace this bearing without taking crankshaft out?

[Sniper]

6 minutes ago, Bryce Mcclintock said:

Can i replace this bearing without taking crankshaft out?

 

Can it be done?  Yes, should it be done?  Well, the only way to answer that would be to pull the crank and measure it out anyway.  With as much play in your thrust, something is seriously worn.

 

 

[Bryce Mcclintock]

Oh dear this sounding expensive 

[Sniper]

8 minutes ago, Bryce Mcclintock said:

Oh dear this sounding expensive 

 

Maybe, maybe not.  If it's just the bearings then not so bad.  But until you can actually measure it and verify we really don't know.  So get the thrust clearance measured and we can go from there.  You may find your eyeball measurement was over generous.

[Bryce Mcclintock]

Haha not the first time . Thanks ill get a dial gauge from someone and find out 

[kencombs]

11 hours ago, Bryce Mcclintock said:

Haha not the first time . Thanks ill get a dial gauge from someone and find out 

You can get a rough measurement with feeler gauges.  Pry the crank in one direction and check the clearance from the bearing thrust face to the crank.  Won't be dead on like a dial gauge, but will tell you if it's really bad.

[Bryce Mcclintock]

Ok guys now ive found knock the whole rear side of thrust bearing it chewed up so im guessing crank will be buggered now too . sigh 

[Sniper]

I am glad you found it, but no so glad at what it was.  The crank may or may not be buggered up, but to be honest you are probably going to have to pull it to figure out if it's useable. 

[Bryce Mcclintock]

Yes i agree ill take it out and get it checked over buy the same guy who working on pistons and rings for me .im sure at worst it can be welded and machined back ...at a price ! Haha . All the other bearings look good is there anything underlying that would cause the the thrust bearing to chew out on back side like that the front and journal still look fine or is this just a age wear and tear thing ?

[Sniper]

Well, every time you press the clutch pedal you put force on that bearing, unavoidable, and doing so when starting is the most aggravating circumstance.  But it's common for them to last the life of the engine.  Since the rest of the engine appears to look ok one has to wonder as to the cause of the failure.  Manufacturing defect?  Contaminate in the oil? some thing else?  hard to say.

 

Here's an article talking about it

 

https://www.motor.com/magazine-summary/thrust-bearing-failure-prevention-analysis/

 

I would inspect the block as well to ensure no damage in that area.  Because if there is it might make sense to find another engine to build.

[grady hawkins]

As strange as it might seem, I had a similar knock at idle in my D24.. turned out to be the rubber on the harmonic balancer had decomposed to the point that it was hitting the frame and making the noise!