Topic: Machine shop took too much off my Cylinder Block/Cylinder Head?

[AintNoEasyWay]

Hey guys, I'm putting together the top end of my 750 K7 & I'm not sure how to move forward because after putting in new dowels, my head doesn't sit flat against my cylinders. I had a local vintage motorcycle shop fix up my valves & I believe they sent the head out to be decked, machined etc. I'll give them a call tomorrow to confirm.

The head sits completely flat against the cylinders if I leave the dowels out, but when I have the dowels in, I can fit a .65 mm feeler gauge in between them. Should I shave the dowels down until they sit flat with the deck of the cylinders? The dowels have a taper at each end that I assume is there for a reason & I don't want to take too much of it off. I'm referring to the inner 8 dowels which are #3 in the diagram below.

Also, my gasket isn't cut for the #2 rubber inserts on the 4 inside (shorter) dowels, as you can see in the photo below. Is it safe for me to leave out those rubber inserts? Some people on the forums seem to have confirmed that's ok. Just want to make sure.

[dusterdude]

Wow,you could have cometic make you a thicker head gasket

[Jerry Rxman Griffin aka MuthaF'er]

Do you have both size dowels/knock pins in the correct locations?

[AintNoEasyWay]

Yea, #8 is significantly longer than #3 in the diagram. I also have them matched up with the old dowels & they're the same size.

[AintNoEasyWay]

Here's a video I took earlier today:

This is with the gasket & rubbery inserts around the dowels. It should still give some general idea of the issue.I know the rubber inserts shouldn't sit flush with the head anyway, that's why I was commenting on maybe torquing everything down. Then I took out the rubber inserts & realized the dowels are the issue.

I'll follow up with the repair shop tomorrow morning & see if they also milled the deck.

[Don R]

 I think someone said the long dowels went in the bottom of the cylinder / crankcase. I'd trim the dowel or swap it for one that works and check the piston / head / valve clearance.

[Eydugstr]

I think someone said the long dowels went in the bottom of the cylinder / crankcase. I'd trim the dowel or swap it for one that works and check the piston / head / valve clearance.

This.  Went through this awhile back, but now the aftermarket sites (Vintagecb750.com) are offering replacement dowels - What I did was buy a new set of dowels and then trim them down.

[AintNoEasyWay]

I think someone said the long dowels went in the bottom of the cylinder / crankcase. I'd trim the dowel or swap it for one that works and check the piston / head / valve clearance.

Actually, the diagram shows #8 dowels go in both the top & bottom of the cylinder block. I can confirm this as I have the 4 originals that I removed from the engine to be replaced.

[AintNoEasyWay]

I think someone said the long dowels went in the bottom of the cylinder / crankcase. I'd trim the dowel or swap it for one that works and check the piston / head / valve clearance.

This.  Went through this awhile back, but now the aftermarket sites (Vintagecb750.com) are offering replacement dowels - What I did was buy a new set of dowels and then trim them down.

Eydugstr, how did you determine how much to trim them down? Did you take the tapered part at the edge of the dowel off entirely?

[AintNoEasyWay]

I just went home for lunch to check things. The two longer dowels that sit at the corners of the cylinder block aren't causing any trouble. I just put them in & the head is able to sit flush with the block.

So, it's the 8 center dowels that are causing the issue. The holes in the head aren't large enough to go over them, so the dowels have to sit completely down into the holes on the cylinder block, otherwise there's a gap. Forum member enwri also suggested I shave the dowels. Would this be ok?

[Powderman]

The dowels are there just to locate the head. Shave them down where they don't interfere and you're good to go. Take the edge to a grinder or sander to bevel it for ease of assembly.

[madmtnmotors]

I just went home for lunch to check things. The two longer dowels that sit at the corners of the cylinder block aren't causing any trouble. I just put them in & the head is able to sit flush with the block.

So, it's the 8 center dowels that are causing the issue. The holes in the head aren't large enough to go over them, so the dowels have to sit completely down into the holes on the cylinder block, otherwise there's a gap. Forum member enwri also suggested I shave the dowels. Would this be ok?

Yes. These are only there to help the barrel shaped seals hold their shape. They are not supposed to protrude into the head. File or grind them down until the interference is eliminated. Use the file to bevel the edges if you like, but not absolutely necessary. Early 750s didn't even use these dowels and seals. Seems to be an effort on Honda's part to resolve weeping head gaskets and was only implemented in later models (post 74 or post 76, somewhere along in there).

[AintNoEasyWay]

Powderman & madmtnmotors, you guys rock. Thanks for your advice!

[koendd]

had the exact same thing with my head on my f2 two days ago.

I shaved them with good result, no leaks on startup

If you want them to be straight, I've put them in my drill and pushed it on some 60grit sandpaper. till the edge was off.

[HondaMan]

That's a strange head gasket you have there: they should either have all 8 of the rubber-dowel holes punched out to 14mm, or else none. If you have the rubber dowels, punch out the ones that are not punched now. The rubber dowels do a superior job of preventing weeping on hot days. They came out on the early K3 engines at the Old Factory, and on the K2 that came from the New Factory, circa 1972.

[madmtnmotors]

Yep. I had a gasket that did not have these holes large enough to accommodate the "barrel" seals. Punched the holes out large enough to use them. Sharpened a piece of thin wall pipe, laid the gasket on a block of wood, used a hammer and the sharpened pipe to punch the holes out.

[AintNoEasyWay]

Just finished shaving the dowels down with a file & used some sand paper to make sure everything is smooth. The head sits flush now! Thanks guys!

I actually ordered this head gasket from David Silver Spares, https://www.davidsilverspares.com/CB750K7-FOUR-1977/part_8011/, & if you enlarge the photo, you can see that it pictures all 8 holes cut to fit the rubber inserts.  I need to find that receipt...

I'll see about punching larger holes tomorrow. That doesn't sound like much trouble at all & could definitely be worth it!

[HondaMan]

Just finished shaving the dowels down with a file & used some sand paper to make sure everything is smooth. The head sits flush now! Thanks guys!

I actually ordered this head gasket from David Silver Spares, https://www.davidsilverspares.com/CB750K7-FOUR-1977/part_8011/, & if you enlarge the photo, you can see that it pictures all 8 holes cut to fit the rubber inserts.  I need to find that receipt...

I'll see about punching larger holes tomorrow. That doesn't sound like much trouble at all & could definitely be worth it!

I have used a [new] sharp Xacto knife, and some patience, to slice thru it layer by layer to get a nice clean hole. For a while I had a 5/6" punch (14.4mm) which also worked perfectly! The hole was slightly smaller than the punch, and it came out right at 14mm.

[koendd]

I don't think there is anything wrong with the gasket.
It's an F2 gasket, only two return are used. other bolts are sealed with o ring at the bottom om cap nut on top

[madmtnmotors]

It's an F2 gasket, only two return are used. other bolts are sealed with o ring at the bottom om cap nut on top

That would definitely work for an F2, but the engine being assembled is a K7.

[koendd]

woops my bad... 

[AintNoEasyWay]

Yea, K7 engine. My dad is going to measure some punches at work for me & I'll probably take the gasket by there during lunch time for customization. 

[AintNoEasyWay]

Just got my gasket cut to fit the 4 other rubber inserts. Just wanted to give an update for anyone who finds this later on. Thanks to all the suggestions everyone made. Problem solved!

[madmtnmotors]

Suhweeet!