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Big Bore head bolts for high boost applications

3782 Views 0 Replies 1 Participant Last post by  GIFF-TURBO
I'm making this post in an effort to illustrate and inform.

Keep in mind -- This information is just my opinion .. .. Yours certinally may vary.

The thread is about the Polaris head bolt and high boost. The problem some are having is the head bolt(s) are pulling out of the case. Perhaps this picture will look familiar to some:

This doesn't seem to be a problem on the stock Polaris engine. The primary reason is -- IF one turns up the boost high enough - The 1st thing to let go is the 3 piece crank.

Enter in the Big Bores ............. Now the problem WILL rear it's ugly head.

1st off -- The head bolt. It's a M11 X 1.25 SEMS -- 8" in length. Meaning the washer is permanently affixed to the bolt during manufacturing. Here's a pic:

Note: The threads are 2 1/2" long. Also look at the top of the head and the underside of the valve cover - This will be important later.

Lets look at the '902 as an example as it relates to the stock head bolt.

1st - The new cylinder is appx. .200" taller. This takes away a few threads on ALL head bolts. This is reason enough for ALL '902's to use a different bolt/stud in this engine.

Here's an even more important reason to consider using longer bolts/studs.

Using the Polaris head bolt torque pic - Bolts 3 and 4 have even shorter threads. Reason -- This is where the hollow dowel pins are located and recess into the threaded hole .260".

Here's some real world numbers for one to consider. In holes 3 and 4 the bolts only grip 14.5 threads. On the remaining 4 holes the bolts grip from 19.5 threads to 23.75 threads.

The 2 shallow holes is where the bolts WILL pull out first - That being holes number 3 and 4. For those of you challenged - Thats the upper left and the lower right holes.

When building this engine - Simply replacing the used head bolts with new ones WILL NOT SOLVE THIS PROBLEM.

Whats the solution ??

1st lets address the case. When this engine heats up -- And believe me .. .. It's quite a heater .......... Aluminum softens and the head bolts start to pull out.

I suggest to not just use longer bolts/studs - But to install Time-serts in ALL 6 bolt holes. You can read up on the benefits of doing this on their web site. Read it and educate yourself.

Now - What does it take to install time-serts and the cost.

Here's where one has several decisions to make.

1st off -- Do you plan on using bolts or studs ?? If you don't know the answer to this question -- Go the ARP's web site and educate yourself.

Then - What size bolt/stud are you going to use. Being you're going to drill out ALL 6 holes - You now have a choice.

One has to keep in mind how much parent material does one have to work with ??

And -- What is available in a bolt/stud ??

Your solution may be different - Butt .......... This is the route I went.

I decided to stay with the Polaris thread of M11 X 1.25 and change the length to 8.5".

By the way - If one views the video Cliff posted of someone installing a time-sert in aluminum V-8 block You are going to have "Issues" !!

I used time-serts universal head bolt kit number 11125. Cost was 396.37

This kit includes 10 - 28mm inserts. This insert is 1.10236" in length and is to be used in holes 3 and 4 only. Order 4 - 30mm inserts at 1.18110" in length and use these 4 in the 4 remaining holes. Reason for using 2 of the 28mm shorter inserts is because of the hollow dowel pin used as this sits .260" into the threaded hole. Cost of the 30mm inserts is 3.25 each.

One point I might forget later -- If you don't install the 28mm inserts flush with the base of the dowel insert hole - Don't panic .......... Simply machine (Grind) off some of the hollow dowel to compensate. Frankly - I recommend taking off .100 anyway as one doesn't want either the cylinder or head to bottom out on the insert and not seal either the base or head gasket.

And on this point -- If you don't seat the insert deep enough into the hole when you install -- Simply grind off enough so the gasket is thicker than what protrudes above the hole.

Here are 2 pic's of 2 correctly installed inserts - One is 30mm long and the other is the 28mm long installed in the hole used by the hollow dowel:

Another tool one might have to order is the TAP handle wrench. I used a No. 6 that I ordered from time-sert and cost 55.23.

One thing -- Read the instructions that come with the kit. UNDERSTAND the instructions that come with the kit. If you don't understand the instructions - Put them under your pillow and sleep on um for a night. You WILL NOT have success if you don't understand and follow the instructions.

Another helpfull tip -- Do this with the engine out of the vehicle. I used my work bench and built an engine stand. Pic illustrating:

In this way - The engine is in an upright position and easy to work around while being held secure. This is most important as you will have to drill and tap. Not good to have the engine moving around.

One thing on using their universal head bolt repair kit -- The alignment block isn't made for this small engine - Butt works very well if you follow this procedure. Use the alignment pin and push hard on it while tightning ONE securing bolt. Only one bolt can be used instead of the 3 the block was machined for. Being carefull this works just fine.

On the starter side of the case there are no component issues interfearing with the alignment block.

On the other side -- IF one is using the HOLZ variable pressure regulator - This has to be removed.

Now to this VERY important point. Use clear 2" box tape and tape the oil hole where you removed the HOLZ oil pressure adjuster.

Follow suit and tape off the complete case covering all 6 head bolt holes. Take a sandwich baggie and place over the 2 rod ends before you tape and tape up the side of the baggie. Then place a rag over everything except the hole you're working on. This WILL prevent any chip from getting inside the engine.

Now - You have prevented any wayward chip from going into the case. When Drilling or tapping I used a shop vac next to the shaft to catch almost all of the chips also.

Use a razor blade or Exacto knife and carefully go around each bolt hole staying away maybe 1/16" from the hole edge and remove the tape. This exposes the hole for machining.

Follow the instructions and they tell how to set up the tools for proper drilling and machining of the insert head and the insert installation. I can't stress enough - For successful insert installation - Read and understand the instructions.

It's my opinion -- When the engine is out of the vehicle and the head and cylinder are removed - Install time-serts whether needed or not.

Note: If you want to use a different length insert -- Other than 22mm/28mm or 30mm - Time-sert has a 1000 minimum order plus special manfacturing fee.

Now - Head bolts or head studs. Studs are the best.

I've been working with Sam Benson at ARP. They will manufacturer anything one wants -- For a price. And that starts at 600 bucks plus a minimum order -- I didn't ask what that was once he mentioned the special fee.

There isn't anything in their on-line catalog. The catalog is vehicle specific.

Butt -- They do stock thousands of bolts/studs of various sizes.

The M11X1.25 isn't that common of a thread size. Butt - They DO have a universal head bolt repair kit in this size !!

Sam was able to come up after several days - A PREMIUM M11X1.25 stud 8.5" long. Their part number is ATP 8.500-2LUGB and is used on at least one Subaru engine.

One then has the option of either a 12pt nut or hex nut. Don't forget to order the washer to. Appx. estimated cost per 3 piece unit is 22 dollars X 6 equals 132.00 for 1 engine.

This stud has 1.5" of thread. Just enough !!

The end of the stud -- The end that goes into the hole -- Has a .300" bullet nose on it. One may have to machine(Grind) this off. I can't comment as My studs haven't arrived yet.

Early on in this posting I mentioned to look at the head and valve cover. Once one installs the stud hand tight - By the way ...... COUNT the threads as you install making sure it's in all the way. Now - Look at the other end of the stud and see if one needs to machine (Grind) some off so the valve cover will seat and seal properly.

I hope this will be of some help to those of you that asked questions and got various degrees of responses.

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