Cylinder head bolt stripped! How do you repair?

15017 Views 11 Replies 3 Participants Last post by EPR, Aug 18, 2012

gera229

Discussion Starter · Aug 16, 2012 (Edited)

One of the bolts on my cylinder head decided to strip.

I road my motorized bicycle and realized it wants to bog down and wouldn't idle so it stalled. The max speed just didn't want to go over 20mph or so, so that's when I checked and found a stripped cylinder head bolt.

I attempted to ride it another 3 miles to get home and while it is bad for the engine if done continuously, 3 miles should not have been enough to be harmful in the long run. So I hope nothing happened to my engine as a result of my terrible decisions and it does look like nothing really happened because once I got home, I pulled the starter and had the engine revv a little when giving it throttle and also pull me. So as you can see, it works and starts up while giving it throttle so I would assume nothing bad happened cylinder/piston wise, so it's not a major concern right now. I did peddle quite a bit to help it and turned the engine off tree times on stops on my 3 mile trip home from when 1 of the cylinder head bolts' stripped.

What is the best way to repair it?

Also this is what the plug looked like when I took it when the engine stalled on me (So yes, when I didn't ride it home yet. The beginning of the 3 miles):

Does this greyish color indicate a perfect mixture?

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CAM2

· #2 · Aug 16, 2012

gera229 said:
One of the bolts on my cylinder head decided to strip.

I road my motorized bicycle and realized it wants to bog down and wouldn't idle so it stalled. The max speed just didn't want to go over 20mph or so, so that's when I checked and found a stripped cylinder head bolt.

I attempted to ride it another 3 miles to get home and while it is bad for the engine if done continuously, 3 miles should not have been enough to be harmful in the long run. So I hope nothing happened to my engine as a result of my terrible decisions and it does look like nothing really happened because once I got home, I pulled the starter and had the engine revv a little when giving it throttle and also pull me. So as you can see, it works and starts up while giving it throttle so I would assume nothing bad happened cylinder/piston wise, so it's not a major concern right now. I did peddle quite a bit to help it and turned the engine off tree times on stops on my 3 mile trip home from when 1 of the cylinder head bolts' stripped.

What is the best way to repair it?

Also this is what the plug looked like when I took it when the engine stalled on me (So yes, when I didn't ride it home yet. The beginning of the 3 miles):

Does this greyish color indicate a perfect mixture?

Having a stripped bolt will cause the engine to suck air at the cap and cause the engine to run lean..It can also cause errosion at the cap and cylinder lip...........

Something tells me you got an engine kit with cylinder head bolts that are too short....The hreads must stick atleast 2-3 threads through the hole...you can see this when the flywheel and clutch arent installed...The head on my 5 port cag loosened twice and stripped once because of thbeing too short.............

the only way to fix it is to get a tap thats the next size up and use heavier duty bolts..............Use loctite too......The plug looks like a descent burn...maybe a tad rich but thats ok because come winter the air will become cooler and drier aswell as thirstier so itll most likely be perfectly jetted to 60 degrees.......Good Luck

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gera229

Discussion Starter · #3 · Aug 16, 2012 (Edited)

Cam2,
This should be a great how-to because I discovered an excellent solution that only took me an hour or less to do.

I bought some extra long hard steel bolts from McMaster a very long time ago when I just started my build. They are M6 and 90MM long. They sent me an extra box of 10 for free because the shipping was delayed. Nice people.

Anyway after 1 hour I fixed it. No need to take the entire cylinder off to re-tap and worry about it stripping again later on; in this case with tapping the next size up, I'd rather use a helicoil thread repair option. The entire kit about $16 shipped: http://www.ebay.com/itm/25-Piece-Th...ultDomain_3&hash=item5ae8eaac6f#ht_542wt_1163

Why? Because I'd be worried about stripping engine threads again.
But then again, there is MINIMAL room for helicoils, so I'm not so sure they would work.

But that's not what I did. I did a 3rd option which has 4 advantages:
1. The easiest.
2. The fastest.
3. The cheapest.
4. Much more reliable than stock.

Here is what I did:
I took an M5 nut, and redrilled and retapped it to M6 size. Thanks to Lowracer from motorbycicling.com for the idea.
Lowracer, however from motorbicycling.com used an M6 size nut so either nut size should fit, I just thought an M5 would fit more perfectly, but with the extra tight fit by using an M6 you would not have to worry about the nut coming off.
The M5 size shouldn't come off either, though. I managed to tighten it really hard without a hex wrench.

Before screwing the bolt and nut together, I spread some red loctite and used washers and lock washers at the top where the bolt goes because they wouldn't fit where the nut goes, but loctite will do the trick instead where the nut goes.

I'm actually happy this thing stripped because otherwise I would not have found this more reliable solution that I can now do to all my bolts and never worry about a bolt coming loose or stripping.

My clone carbon black reeds seem to be good so far. I want to go back to the stock tin reeds just because I was told they will last longer so it will save me hassle later, but I just don't want to go with replacing the gaskets all over again and scraping the stuck on gaskets off with a knife or something. It's a pain to remove gaskets and can damage the engine block casing.

Plus I don't think the black carbon reeds give any better performance than the tin reeds because they are clones.
While they last I guess I will just keep them in there, they seem to be sealing well.
I don't know how to check how well they are sealing and I don't know what will happen if they don't seal well, but if nothing seems to be wrong with my engine and it's running good, then I'm assuming that the reeds are sealing well.

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EPR

· #4 · Aug 16, 2012

I was just going to tell you get a longer bolt, sealer and a locknut, but you figured it out. I have an engine I did that too it still runs great 18 months later. That was your problem, I'm pretty sure, it's like Cam2 said, it's happened to me too.

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gera229

Discussion Starter · #5 · Aug 16, 2012

Too short of a bolt was not my problem lol. I already had a longer bolt in there.
What is a bolt sealer EPR? You mean loctite?

What size nut did you use EPR? M5 (re-tapped to M6) or M6?

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gera229

Discussion Starter · #6 · Aug 16, 2012

Oh an EPR, this would be the most helpful how-to for many people. I'm surprised it nobody made a thread with a sticky of the how-to because then I wouldn't have to search back to your post in an unrelated titled thread lol.

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CAM2

· #7 · Aug 16, 2012

gera229 said:
Cam2,
This should be a great how-to because I discovered an excellent solution that only took me an hour or less to do.

I bought some extra long hard steel bolts from McMaster a very long time ago when I just started my build. They are M6 and 90MM long. They sent me an extra box of 10 for free because the shipping was delayed. Nice people.

Anyway after 1 hour I fixed it. No need to take the entire cylinder off to re-tap and worry about it stripping again later on; in this case with tapping the next size up, I'd rather use a helicoil thread repair option. The entire kit about $16 shipped: http://www.ebay.com/itm/25-Piece-Th...ultDomain_3&hash=item5ae8eaac6f#ht_542wt_1163

Why? Because I'd be worried about stripping engine threads again.
But then again, there is MINIMAL room for helicoils, so I'm not so sure they would work.

But that's not what I did. I did a 3rd option which has 4 advantages:
1. The easiest.
2. The fastest.
3. The cheapest.
4. Much more reliable than stock.

Here is what I did:
I took an M5 nut, and redrilled and retapped it to M6 size. Thanks to Lowracer from motorbycicling.com for the idea.
Lowracer, however from motorbicycling.com used an M6 size nut so either nut size should fit, I just thought an M5 would fit more perfectly, but with the extra tight fit by using an M6 you would not have to worry about the nut coming off.
The M5 size shouldn't come off either, though. I managed to tighten it really hard without a hex wrench.

Before screwing the bolt and nut together, I spread some red loctite and used washers and lock washers at the top where the bolt goes because they wouldn't fit where the nut goes, but loctite will do the trick instead where the nut goes.

I'm actually happy this thing stripped because otherwise I would not have found this more reliable solution that I can now do to all my bolts and never worry about a bolt coming loose or stripping.

My clone carbon black reeds seem to be good so far. I want to go back to the stock tin reeds just because I was told they will last longer so it will save me hassle later, but I just don't want to go with replacing the gaskets all over again and scraping the stuck on gaskets off with a knife or something. It's a pain to remove gaskets and can damage the engine block casing.

Plus I don't think the black carbon reeds give any better performance than the tin reeds because they are clones.
While they last I guess I will just keep them in there, they seem to be sealing well.
I don't know how to check how well they are sealing and I don't know what will happen if they don't seal well, but if nothing seems to be wrong with my engine and it's running good, then I'm assuming that the reeds are sealing well.

Nice job getting it fixed.........

If you did 1 why not do all 4?

On my builds I put a nut on both sides...............

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gera229

Discussion Starter · #8 · Aug 16, 2012 (Edited)

Cam2, does the M6 nut fit right in like the M5 (re-tapped to M6 size) nut that I have?
It looks like there's not a lot of room for an M6 outside diameter. The M5 outside diameter is smaller by about 2mm.

I've been asking this question, but no answer yet lol.

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EPR

· #9 · Aug 17, 2012

I like the Cag engine cause, all the cylinder bolts are on the outside, so when I ran my M6 x 1.0 tap thru the bolt hole no metal can get inside the eng. All my Cags are M6 on the cyld bolts. My Red Head 49cc Zen, they are M5 x 0.8, I was to lazy to drill and retap them to M6, but I got 4, M5 x 0.8 x 75mm long carb bolts from Davesmotors and put nut on top of the Clyd flanges and lock them down and alittle blue thread sealer. On all my engines, I re tap Every Hole on the engine, and buy grade 5 , 8.8 socket head bolts and SS washers, star or split.

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CAM2

· #10 · Aug 17, 2012

gera229 said:
Cam2, does the M6 nut fit right in like the M5 (re-tapped to M6 size) nut that I have?
It looks like there's not a lot of room for an M6 outside diameter. The M5 outside diameter is smaller by about 2mm.

I've been asking this question, but no answer yet lol.

Seeings theres about 5-6 different manufacturers of these heads and cases each will vary a lil....On my redheadded 3 port 2 pc engine I had to grind away the head a lil to clear the nuts on top and gring the nuts on one side to fit behind the clutch and flywheel.........I also had to grind the nuts on one side on my 5port 2pc head cag aswell so theyll secure the headbolts

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gera229

Discussion Starter · #11 · Aug 18, 2012

Do you put washers where the nuts go at the bottom? As you can see, I didn't use a washer.

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EPR

· #12 · Aug 18, 2012

I use flat #10 SS washers on M5 bolts and 1/4" SS for M6. The washers just keeps the nuts from digging into the base metal when they seat. The only one I have stripped, It's Mr. OverTighten everything got carried away,lol.

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