Bike has been not running correctly for about a week. At first I thought I had a exhaust leak from the front head but then I was advised to spray some WD40 on the intake flanges.

At that point the sound was a very loud "popping" as well as a small blue flame from the top of the front pushrod on the front head.

Sounds like a blown head gasket, any good tech folks that would agree? I have zero tech skills but we are going to run a compression test this weekend and go from there.

I really don't want to drop off at a HD dealer and pay roughly $78/labor hour plus parts.

Any recommendations?

 

Run the compression test; if compression looks OK, run a leak down test and post the results. Make sure to hold the throttle wide open when checking compression. Don't know how many miles but might be a good opportunity to freshen up the top end??

 

Typically, spraying a volatile material toward the intake flanges is to test for an intake leak ... sometimes the gasket material will separate from the head and cause an intake leak ... this can cause the bike to run lean ....

The compression test should indicate whether the seal on the combustion chamber is good ... i.e., whether the valves seat, rings hold compression, gasket seal is good ....

The intake leak check procedure in the service manual has you use a bottle of propane with a tube ... you open up the valve on the bottle while holding the tip of the tube around the intake manifold flanges ... if the motor revs up it is because the fuel mixture is being enriched by the propane that is coming in from the intake leak ....

I would think a blown head gasket is an extremely rare event ... could be ... but, would think it less likely than another culprit ....

* * *

If you could provide a little better description of your symptoms it will allow forum members more info to help you troubleshoot the problem ....

R/
'Chop

 

IF a cylinder head gasket is needed, then a Cometic MLS EST set will not have you attending to this again, any time soon.
Scott

 

Excellent point.

My problem started 8 days ago after I rode to work in the morning...no problems. Then when leaving work, as I started the bike a "hissing" sound was coming from the front end. I couldn't find any obvious air leaking but initially I was thinking some sort of exhaust leak. The bike ran fine though with the one exception of a bit more backfiring as I left off the throttle.

Then I sprayed the WD40 and the "hiss" was gone and replaced by a "popping" sound. As well the escaping air could be found near the front head lower end and again, the small blue type of flame from the top of the pushrod.

 

Replace the head gasket with a Cometic. Go strictly by the Service manual and all will turn out well.If you have more questions, check back in.

 

More update on this situation.

A very good friend that has re-built many engines on HD's and choppers came to look at my problem today. As soon as we fired the bike up, he had an idea instantly what the problem is.

He grabbed a stethiscope and had me start the bike again. This time he listened to the cams and heads themselves. He said the back head and cams sound fine.

His belief is that the gasket on the front head where the top piece and bottom piece connect is the damaged part. This is where the escaping air seems to be coming from as well.

So Monday I will make some phone calls to see prices. Has anyone ever done a repair like this themself? Can the head be worked on without removing from the body?

 

The motor doesn't have to be removed. The front head is easier to work with than the rear, more room to remove rocker boxes. You start by removing the gas tank and then the intake. You need a service manual to do this correctly, the best investment you'll ever make on your bike.

 

Going to buy the service manual tomorrow!

And thank you...looks like that is the route we are going to work is buying the parts and then getting to work on the weekends.

 

R&R the head gasket is not difficult; if you have the parts and tools, you can finish in a day, even if this is you first time. If you use the Cometic gaskets, be sure you get the thickness that is as close to the compressed thickness of the stock gaskets; the Cometic MLS gaskets don't compress like the OEM gasket. IIRC, the OEM head gasket compresses to a thickness between .040" and .045"; .042" is commonly used. A compression imbalance on the Twin Cam engine is not desireable.

If you do decide to use Cometic, you will not need the orings at the oil return dowels.

You should plan to buy some 1/2" PVC couplings to use to secure the cylinder to the base. If you should break the seal at the base of the cylinder, you might want to pull the cylinder and relace the cylinder base oring. Some will debate the need to pull a cylinder and replace the base oring in that situation. I would rather do it while was "there" rather than take a chance and have an oil leak later.

I don't know what year the bike is but if an earlier model with the plastic breathers, consider upgrading to the metal breathers; cheap upgrade.