How To Do A Cranking Compression Check On A Harley Davidson Motorcycle

[@trevellyanblack4101]

Although we’ve all learnt through trial and error the folly of not reading the workshop manual, there’s just something about being shown what to do that’s irreplaceable. As such, with every Hammer Dan video I watch, I’m starting to feel that I’m doing an apprenticeship. Priceless and thanks! Lol

[@huka_ro7852]

So true. Same here, learning a ton!!

[@kendellc9924]

Great video! I remember when I thought I toasted my cylinder sleeves cuz I was getting readings around 90psi. I wanted to kick my own ass so bad until Hammer Dan called and reminded me that we went with ez-start cams which won't show a true compression reading at cranking rpms. HUGE sigh of relief after that phone call! Thanks again all you guys up there.

[@jonnymac8925]

Which cams did you go with?

[@kendellc9924]

@@jonnymac8925 S&S EZ Start 585's. They're a little too hot for the ideal cruise through the mountains. Wish I had more midrange. But when they wake up, they really scream. Here's the link to their video tuning my bike kzbin.info/www/bejne/ioO9haqop9Ciia8

[@CarlosGarcia-ls4hn]

What is the procedure for a bike that has compression releases?

[@tvd1188]

great vid, would love to see the leak down next.

[@bobmetzger51]

Thanks for the video. Great information. Much appreciated.

[@jasonpotenziani3176]

Nice tip

[@huka_ro7852]

Thank you for another very informative video 👍👍

[@robedmunds7163]

Main thing you missed out here is it is not just the psi, it is important that both cylinders give similar readings. If one is low compared to the other you have a problem

[@codybatman7974]

How large of a difference between cylinders is okay?

[@robedmunds7163]

@@codybatman7974 much more than 10 psi and I would think something is up. Usually it is the rear cylinder that is lower as it runs a bit hotter.

[@kennethwise7108]

Why do some people swear on grounding the spark plugs ? I've seen and read that failure to do so can and will fry your ignition and or module. Thanks for sharing your insights

[@nyinehinnocentfuntong5209]

Yes sir thank you very much for this one but what I really like to know is what is the psi for a leaking valve or leaking ring

[@eddiesargent4163]

Top notch guys!!👍👍

[@thakery5720]

Quoting my 2006 H-D service manual, 1200cc engines normal compression is 200 to 225 PSI.... no wonder it would sometimes 'rattle' with pre-ignition on hot days..... I was getting 211 and 215 with one of your 1250 kits (rectangular dome 10.5 :1 pistons) and Andrews N4 cams. I have since bought your Impact 560 cams and use Ultima roller rockers with a slight ratio increase and had the heads ported over here in England. The porter found my heads needed decking to get the nominal 62cc (or whatever it is ! ) due to some other guy's seat work.... I have found my compression tester again, so will be interested to see what it tells me.....

[@jonnymac8925]

It's been a while but do you remember your results?

[@thakery5720]

@@jonnymac8925 No, sorry but I haven't put the compression tester on it yet and it may be a while before I get the chance. I managed to lose control at low speed and slip into a gulley - long story short, the bike is not too bad but I have a broken tibia and fibula that required the use of a Llizarov frame (look it up). I would not think the cranking pressures are much higher than H-D quote for a standard bike though as although Hammer's static compression ratio is higher than Harley's standard XL1200R, the later closing point of Hammers inlet cam will reduce the overall cranking pressure

[@illla]

Doing compression test on Buell XB is nightmare.

[@ratjaw75]

Anyone else notice the gauge wasn't zeroed? Anyway great video. Can't wait 'till I can order the 1275 kit from you guys for my old Sportster.

[@rickdecarlo]

Starts at about 20

[@Si-Toecutter]

You don't turn off the gas?

[@paulbouverette503]

2016 Street Glide, does it matter if my bike is fuel injected? Still wide open on the throttle? Would I do everything the same? What compression should I expect from a stock 103 engine?

[@tompava3923]

Hey Hammer Dan. I’ve been catching a lot of your vids and I have noticed when you talk about “earlier model Sportsters“ you don’t usually go back to include the four-speed motors. Are they that different, that it would require a whole new video, or that similar that they don’t need to be addressed directly? I have an ‘86 883 and I am interested in a performance package including cams and headwork. Just wondering if I am in for a surprise when I read the install instructions? I’ve been working on Harleys off and on since the 70's but have yet to deal with the cams or lower end/transmission on a sportster. Very much appreciate all of the info available here! Such great resources we have at our disposal! ( I am asking this question here, because most of the other videos were more than a year old and I thought it might get missed)

[@theoldboyscout3662]

Do I need to disconnect fuel on an injected 96 twin cam? And do I leave the plugs connected and ground them to the bike or just pull the fuse for the ignition?

[@konstantinbedin9891]

Hi! But what about the ignition coil disconnection?

[@HAMMERPERFORMANCE]

just need to pull the plugs and disconnect the wires from them.

[@jonnymac8925]

What's your opinion on running race fuel on a late model bike with 190-210?

[@goodboyringo9716]

Removing spark plugs on a hot engine alum cylinder could strip the threads . On a warm engine they may be ok to remove.

[@boatman19607]

I realize this video is old and I'm not at all questioning Hammer Dan (love you guys) but just wanted to add I was always told to warm up the engine first prior to the testing too.

[@IronManMoto]

he already said that in the video

[@PatsyHall-fl1gq]

If my oil pump gear has went as far as leaving metal pieces in the oil pump is the motor gone

[@HAMMERPERFORMANCE]

It can be repaired, so I'd stop short of calling it "gone". But it's a mess, generally requiring a full tear-down to really clean it out properly and assess potential damage to cylinder walls and bearings and so forth. Failure of that gear is unfortunately not uncommon, particularly when the power is raised. It was a terrible issue on Buell models because they made a lot more power. HD finally came out with a fix in 2006, in the form of a bronze gear that conforms to the varying tooth engagement that results from pinion shaft runout. Watch this video for more information: kzbin.info/www/bejne/rpaolHacrdhgpNU

[@midas61]

Maybe something you forgot to mention here....What about the status of fuel carb/EFI when you do the test? Carb....fuel off, run till float bowl empty, then test? EFI......?

[@deckardvostok2203]

What readings should I be expecting by doing this with a cold engine and without WOT on a fatboy 103 ci? The manual also states to take off the air cleaner, Is it really necessary to do that? Your answer will be much appreciated.

[@HAMMERPERFORMANCE]

A compression test without holding the throttle wide open is invalid, and you shouldn't draw any conclusions from the result. If the motor can't draw in air, it can't make compression.

[@deckardvostok2203]

@@HAMMERPERFORMANCE Ok thank you so much for your quick answer.........The reason I ask this is I have an electronic throttle so I'm not quite sure it will work with the plugs out when I push the start button.....anyways if I do this with completely WOT, cold engine and air filter on, what readings should I be expecting from this particular 103 motor? Thanks again. P.D. I also have ACRs on the heads

[@garrettholt8314]

Was this an 883?

[@techunity1401]

My 1999 1200 sportster has 90 psi in both cylinders. Is this really bad? It’s way low.

[@HAMMERPERFORMANCE]

With the throttle wide open?

[@techunity1401]

@@HAMMERPERFORMANCE I used a gauge and put it in the spark plug hole and just turned the engine over a couple times while having both spark plug wires disconnected so it wouldn’t start.

[@HAMMERPERFORMANCE]

@@techunity1401 A compression test has to be done with the throttle wide open. If not, then the motor can't pull in air, and it makes the result come out way low. Do it again with the throttle wide open and I think you'll see a much better result.

[@techunity1401]

@@HAMMERPERFORMANCE thank you, my dyna had 150psi and my dads Electra glide had 120psi doing it with no throttle also.

[@danielgagne485]

can someone explain the relationship of psi to ratio...(i.e. say 165 psi is equal to 9.2 to one)

[@HAMMERPERFORMANCE]

It can be calculated, however, cam timing is a part of the calculation. We offer a free calculator program and we have a video that shows how to use it: kzbin.info/www/bejne/rJjGna1pe7SklbM

[@jonnymac8925]

@@HAMMERPERFORMANCE how accurate is the calculator? Thanks!

[@josephsimons5513]

How do you determine the compression ratio when you take the readings on each cylinder ie: a 215 reading is 10:1 or 12:1? I have a 2010 fat Bob and I want to replace the plugs right plug for compression ratio

[@HAMMERPERFORMANCE]

To get from compression ratio to cranking compression, you have to factor in cam timing, specifically the intake valve close point. Watch this video, we show how it's done: kzbin.info/www/bejne/rJjGna1pe7SklbM