Compression tester needed

[Nathan k]

Hi

Viewing a rib tomorrow with a 40hp yamaha 2 stroke but completly forgot about testing the engine for compression
I can't sea trial so it's vital I get one
Does anyone know where I can buy one tomorrow morning? or does anyone have one that I could borrow for a few hours?

also is this right;
Disconnect fuel line
remove spark plug and screw in compression tester
turn engine over and read compression
repeat for all cylinders

what should compression should I be looking for in a 40hp Yamaha?

Thanks

Nathan

[Boats&Outboards]

Don't forget to remove the kill cord to cut off any spark.

Your looking for the tolerance levels to be within 10 % tops. A reading of 130 would be about right but expect anything from 115-150 dependant on age, use etc. Repeat when warm too

Not local but most car auto shops such as Halfords will stock (but they will sting you for one) it. Just be sure it's either got the correct fitting or adapters to suit.

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

[Nathan k]

Thanks Peter, how do I know what adapter I need?

[Nasher]

Nathan.

I've a couple knocking about in the garage, with adaptors for different size plug holes.

If you can get up to Clanfield just up the A3 South of Petersfield before viewing the engine you are welcome to borrow one.

Other than that I'd also suggest Halfords, but also Machine Mart.

I'll PM you a telephone number.

Nasher.

[Vandad]

130 is way too high, anything above 100 is fine IMO. Just look for the difference between the cylinders as Peter mentioned anything above 10% then you should just invetsigate the reason.

One engine I owned had flooded carb, I could see one cylinder does not spark, and then the compression test on that particular cylinder was higher than the other cylinders.

A compression difference does not necessary mean a defect cylinder or piston ring etc..

Halfords sell tester with both adapters and be careful as the battery may die on you if the battery is not charged.

[Chris]

I think you are meant to open the throttle fully when compression testing?

[Boats&Outboards]

Good advice. Keep us posted on what the readings are and how you get on

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

[Nathan k]

Originally Posted by Boats&Outboards

Good advice. Keep us posted on what the readings are and how you get on

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

Will do!

would this be ok? Halfords | Gunson Hi-Gauge Compression Tester

[Boats&Outboards]

Looks good to me (although as discussed you can get cheaper ones but not so quick/easy check out the pic).

From memory a Yam 40 will have something similar to a BR7HS-10 (NGK) which has a 14mm thread diameter. Might be worth double checking with Yam in the morning though

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

[Nathan k]

Thanks for all the advice, i would buy online i just don't have the time.

Anyway i've got a early start for a change. no more 12am lay ins...
I'll give yam a call in the morning

[bedajim]

Don't you remove all of the spark plugs ?

[CornishRoss]

Hi Nathan,

The compression tester I've got came from a bike shop called Hein Gericke. It came with two adapters and two universal adapters, which are rubber cones that you have to push into the spark plug hole. The universal adapters aren't ideal and will be tricky if engine is pull start but will get the job done if your stuck.

Might be worth looking for a bike store if your stuck.

Let us know how you get on and what the compression figures are. I tested my 50hp the other day but can't find any official figures on what the compression should be.

[Nathan k]

Compression was 121 125 120

[Boats&Outboards]

Sounds about right and as I expected. I personally would have been a little concerned at readings of 100 as that could indicate more wear to cause it to drop from new which would yeild at least 130 upto as much as 150 maybe more I'm not sure on factory specs,

but then it depends on age too and I'd rather have 3 at 100 than 2 at 130 and the 3rd on 110 etc.

The question is now then, did you buy it ?

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

[CornishRoss]

Crickey that's some accurate compression tester you got your hand on! What type was it? Did you do the test with the engine warm?

And the big question did you buy it?

[Nathan k]

I did, the engine was 2004 and sold in 2005, around 80 hours. very nice engine and average boat. nothing wrong with the boat and i can't complain considering the price!
Can't wait to test it out, got some more boating gear today all ready to brave the rain tomorrow
I finally own a rib! woohoo!

pictures of it here:
http://www.rib.net/forum/f9/wanted-4...rib-45328.html

[CornishRoss]

Congratulations looks like a nice package!

[whisper]

Well done Nathan, welcome to the Searider gang

[Boats&Outboards]

Nice. Well done that man!

I'm guessing this is not the Rib your planning on doing the round Britain thing in but all the same your going to have some great fun with that one. Enjoy!

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

[Neil Harvey]

so when and where is the maiden trip out?