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717 95psi after rebuild

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beatnik

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Specs is 0.004 - 0.0045 (0.10mm). And machine shop was instructed to do so. When I measured after the job (new sleeve, bore/hone), it's 0.0055 (0.14mm), with wear limit as per manual 0.008(0.2mm). What could be the compression for this clearance?.

Flooded with oil, let it run on starter a little bit, to seat the ring, 95psi
Could this larger than spec clearance cause this, or do I need to look for something else?.

Will I have compression after rebuild, and running with oil, or do I need to run it for xx mins.
 
That clearance will not affect compression. You likely have a bad compression gauge. Did you measure the ring "end gap" ?? You could have an O-ring unseated or missing on the head.
 
End gap was 0.12mm, orings are new surfaces are cleaned. I have two compression gauges (old and brand new) both gauges have same reading. And both cylinders have same reading.
 
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I've done top ends with piston clearance of .007" with no compression issues. End gap I encounter on WSM pistions with new bores and (,005") clearance is generally ( .018" - .020") Since it is WSM and their design I leave them as is and I never had trouble with compression. It's always 150psi or a tad higher. Damaged rings and worn cylinders can be 130psi. I would suggest you check other places for compression loss. Those readings are way off. Good Luck.
 
Agreed, I have never seen fresh cylinders be lower than 150 psi even before being broken in.
 
Throttle open. Reassembled again, cleaned screws from old loctite, made sure rings are sealed but no success. The thing that was wrong last time I had the cylinders mixed, but put them back on their old spot and still same 95psi.

Do I need to have exhaust or anything else connected before test, does not see like it for me?.
 
I think it might be that the internal oring is not sealing (both new), I was replacing sleeves maybe they are too far down?. Also when I took the head out it had oil in the place where oring should be. So proving that it does not seal. Any idea how to go past this, other yha putting extra sealant, adding extra torque (did with the specs 24). 20220717_093129.jpg
 
Your supposed to seal that oring with Loctite 515 and use the Loctite spray on the aluminum before applying the loctite.
 
Jenks13 said:
Your supposed to seal that oring with Loctite 515 and use the Loctite spray on the aluminum before applying the loctite.
Click to expand...
Does not say it in the manual I have, and it's kinda low temp, use it for cam cover for cars. But will give it try!. Thanks
 
Jenks13 said:
Your supposed to seal that oring with Loctite 515 and use the Loctite spray on the aluminum before applying the loctite.
Click to expand...
I've never used anything but grease on those o-rings "light coat". No problems. O-rings don'tneed help to seal unless there is some damage. If loctite is used and the joint it has to come apart for any reason it's a nightmare to clean.
 
Assembled with 518 and its still 95psi, did not measured squish ad just found out I have 3 thickness of gaskets in the set. Could this affect compression in such a great deal?
 
Measured squish changed gasket to thinner assembled on 518, needed to drop one helicoil since damaged the thread. if no compression tomorrow will throw it down the river.
 
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125psi now without oil. Cannot crank with oil, seems like the clearance is too big. Should I try iwith 125psi?
 
beatnik said:
Specs is 0.004 - 0.0045 (0.10mm). And machine shop was instructed to do so. When I measured after the job (new sleeve, bore/hone), it's 0.0055 (0.14mm), with wear limit as per manual 0.008(0.2mm). What could be the compression for this clearance?.

Flooded with oil, let it run on starter a little bit, to seat the ring, 95psi
Could this larger than spec clearance cause this, or do I need to look for something else?.

Will I have compression after rebuild, and running with oil, or do I need to run it for xx mins.
Click to expand...
Have you by any chance checked clearance of the valve and side cover?
 
What do you mean, “when I add oil”? What are you adding oil to when trying to crank?
 
beatnik said:
No I did not opened the bottom.. but when I add oil the starter cannot turn the crank fast its such a compression so must be the piston too wall to large
Click to expand...
I would have to agree with etemplet that the compression tester may be bad and the valve cover and clearance is under the side cover which is under the carbs. If the clearance is too great then the compression will be very low even with new cylinders pistons and rings. Happened to me on my 581.
 
Have two compression testers, clearance is 0.06 so almost maxed. Going for a vacation in one week, for 2 weeks. Unsure if to use it or replace again (+bore, hone) the pistons.
 
I did find this online. But maybe the piston you received (I’m assuming in a rebuild kit) might be undersized?
 

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Stop adding oil to check compression, this isn’t a 4-stroke and isn’t going to do anything but give you false information.

Get it running rev it up to burn out the extra oil then check compression.

If it’s still low then something is obviously wrong. Compression doesn’t just magically fix itself. You either have the wrong size pistons and or bore or wax too much squish clearance, that’s about the only options.
 
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